Arctic ocean

A one-dimensional thermodynamic model of sea ice is presented that includes the effects of snow cover, ice salinity, and internal heating due to penetration of solar radiation. Surface-energy balances determine rates of ablation and accretion; diffusion equations govern heat transport within the ice and snow. The incoming radiative and turbulent fluxes, oceanic heat flux, ice salinity, snow accumulation, and surface albedo are specified as functions of time. Starting from an arbitrary initial condition, the model is integrated numerically until annual equilibrium patterns of temperature and thickness are achieved. The model is applied to the central Arctic. Input values for the initial test of the model are based on observational data. Values predicted by the model for the average ice thickness (288 cm), amount of surface ablation (40 cm), and the temperature field all agree closely with field observations. Other results from the model indicate that, under present conditions, the ocean must supply 1 to 2 kcal/cm2 year to the ice; an additional 4 kcal/cm2 year would cause the ice to vanish. Annual snow depths less than 70 cm are shown to have little effect on equilibrium thickness; snow depths greater than 70 cm would result in much thicker ice. Comparison of observed and calculated temperature profiles suggest that about 2.0 to 2.5 kcal/cm2 year of the incoming short-wave radiation penetrates the ice and contributes to internal heating. Average ice albedos under 0.50 would cause the ice to vanish in a few years.

@article{doi101029jc076i006p01550,
    author = "Maykut, Gary A. and Untersteiner, Norbert",
    title = "Some results from a time-dependent thermodynamic model of sea ice",
    year = "1971",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "A one-dimensional thermodynamic model of sea ice is presented that includes the effects of snow cover, ice salinity, and internal heating due to penetration of solar radiation. Surface-energy balances determine rates of ablation and accretion; diffusion equations govern heat transport within the ice and snow. The incoming radiative and turbulent fluxes, oceanic heat flux, ice salinity, snow accumulation, and surface albedo are specified as functions of time. Starting from an arbitrary initial condition, the model is integrated numerically until annual equilibrium patterns of temperature and thickness are achieved. The model is applied to the central Arctic. Input values for the initial test of the model are based on observational data. Values predicted by the model for the average ice thickness (288 cm), amount of surface ablation (40 cm), and the temperature field all agree closely with field observations. Other results from the model indicate that, under present conditions, the ocean must supply 1 to 2 kcal/cm2 year to the ice; an additional 4 kcal/cm2 year would cause the ice to vanish. Annual snow depths less than 70 cm are shown to have little effect on equilibrium thickness; snow depths greater than 70 cm would result in much thicker ice. Comparison of observed and calculated temperature profiles suggest that about 2.0 to 2.5 kcal/cm2 year of the incoming short-wave radiation penetrates the ice and contributes to internal heating. Average ice albedos under 0.50 would cause the ice to vanish in a few years.",
    url = "https://doi.org/10.1029/jc076i006p01550",
    doi = "10.1029/jc076i006p01550",
    openalex = "W2056294409",
    references = "doi102307140764"
}

Deep‐sea drilling in the Antarctic region (Deep‐Sea Drilling Project legs 28, 29, 35, and 36) has provided many new data about the development of circum‐Antarctic circulation and the closely related glacial evolution of Antarctica. The Antarctic continent has been in a high‐latitude position since the middle to late Mesozoic. Glaciation commenced much later, in the middle Tertiary, demonstrating that near‐polar position is not sufficient for glacial development. Instead, continental glaciation developed as the present‐day Southern Ocean circulation system became established when obstructing land masses moved aside. During the Paleocene (t = ∼65 to 55 m.y. ago), Australia and Antarctica were joined. In the early Eocene (t = ∼55 m.y. ago), Australia began to drift northward from Antarctica, forming an ocean, although circum‐Antarctic flow was blocked by the continental South Tasman Rise and Tasmania. During the Eocene (t = 55 to 38 m.y. ago) the Southern Ocean was relatively warm and the continent largely nonglaciated. Cool temperate vegetation existed in some regions. By the late Eocene (t = ∼39 m.y. ago) a shallow water connection had developed between the southern Indian and Pacific oceans over the South Tasman Rise. The first major climatic‐glacial threshold was crossed 38 m.y. ago near the Eocene‐Oligocene boundary, when substantial Antarctic sea ice began to form. This resulted in a rapid temperature drop in bottom waters of about 5°C and a major crisis in deep‐sea faunas. Thermohaline oceanic circulation was initiated at this time much like that of the present day. The resulting change in climatic regime increased bottom water activity over wide areas of the deep ocean basins, creating much sediment erosion, especially in western parts of oceans. A major (∼2000 m) and apparently rapid deepening also occurred in the calcium carbonate compensation depth (CCD). This climatic threshold was crossed as a result of the gradual isolation of Antarctica from Australia and perhaps the opening of the Drake Passage. During the Oligocene (t = 38 to 22 m.y. ago), widespread glaciation probably occurred throughout Antarctica, although no ice cap existed. By the middle to late Oligocene (t = ∼30 to 25 m.y. ago), deep‐seated circum‐Antarctic flow had developed south of the South Tasman Rise, as this had separated sufficiently from Victoria Land, Antarctica. Major reorganization resulted in southern hemisphere deep‐sea sediment distribution patterns. The next principal climatic threshold was crossed during the middle Miocene (t = 14 to 11 m.y. ago) when the Antarctic ice cap formed. This occurred at about the time of closure of the Australian‐Indonesian deep‐sea passage. During the early Miocene, calcareous biogenic sediments began to be displaced northward by siliceous biogenic sediments with higher rates of sedimentation reflecting the beginning of circulation related to the development of the Antarctic Convergence. Since the middle Miocene the East Antarctic ice cap has remained a semipermanent feature exhibiting some changes in volume. The most important of these occurred during the latest Miocene (t = ∼5 m.y. ago) when ice volumes increased beyond those of the present day. This event was related to global climatic cooling, a rapid northward movement of about 300 km of the Antarctic Convergence, and a eustatic sea level drop that may have been partly responsible for the isolation of the Mediterranean basin. Northern hemisphere ice sheet development began about 2.5–3 m.y. ago, representing the next major global climatic threshold, and was followed by the well‐known major oscillations in northern ice sheets. In the Southern Ocean the Quaternary marks a peak in activity of oceanic circulation as reflected by widespread deep‐sea erosion, very high biogenic productivity at the Antarctic Convergence and resulting high rates of biogenic sedimentation, and maximum northward distribution of ice‐rafted debris.

@article{doi101029jc082i027p03843,
    author = "Kennett, James P.",
    title = "Cenozoic evolution of Antarctic glaciation, the circum-Antarctic Ocean, and their impact on global paleoceanography",
    year = "1977",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Deep‐sea drilling in the Antarctic region (Deep‐Sea Drilling Project legs 28, 29, 35, and 36) has provided many new data about the development of circum‐Antarctic circulation and the closely related glacial evolution of Antarctica. The Antarctic continent has been in a high‐latitude position since the middle to late Mesozoic. Glaciation commenced much later, in the middle Tertiary, demonstrating that near‐polar position is not sufficient for glacial development. Instead, continental glaciation developed as the present‐day Southern Ocean circulation system became established when obstructing land masses moved aside. During the Paleocene (t = ∼65 to 55 m.y. ago), Australia and Antarctica were joined. In the early Eocene (t = ∼55 m.y. ago), Australia began to drift northward from Antarctica, forming an ocean, although circum‐Antarctic flow was blocked by the continental South Tasman Rise and Tasmania. During the Eocene (t = 55 to 38 m.y. ago) the Southern Ocean was relatively warm and the continent largely nonglaciated. Cool temperate vegetation existed in some regions. By the late Eocene (t = ∼39 m.y. ago) a shallow water connection had developed between the southern Indian and Pacific oceans over the South Tasman Rise. The first major climatic‐glacial threshold was crossed 38 m.y. ago near the Eocene‐Oligocene boundary, when substantial Antarctic sea ice began to form. This resulted in a rapid temperature drop in bottom waters of about 5°C and a major crisis in deep‐sea faunas. Thermohaline oceanic circulation was initiated at this time much like that of the present day. The resulting change in climatic regime increased bottom water activity over wide areas of the deep ocean basins, creating much sediment erosion, especially in western parts of oceans. A major (∼2000 m) and apparently rapid deepening also occurred in the calcium carbonate compensation depth (CCD). This climatic threshold was crossed as a result of the gradual isolation of Antarctica from Australia and perhaps the opening of the Drake Passage. During the Oligocene (t = 38 to 22 m.y. ago), widespread glaciation probably occurred throughout Antarctica, although no ice cap existed. By the middle to late Oligocene (t = ∼30 to 25 m.y. ago), deep‐seated circum‐Antarctic flow had developed south of the South Tasman Rise, as this had separated sufficiently from Victoria Land, Antarctica. Major reorganization resulted in southern hemisphere deep‐sea sediment distribution patterns. The next principal climatic threshold was crossed during the middle Miocene (t = 14 to 11 m.y. ago) when the Antarctic ice cap formed. This occurred at about the time of closure of the Australian‐Indonesian deep‐sea passage. During the early Miocene, calcareous biogenic sediments began to be displaced northward by siliceous biogenic sediments with higher rates of sedimentation reflecting the beginning of circulation related to the development of the Antarctic Convergence. Since the middle Miocene the East Antarctic ice cap has remained a semipermanent feature exhibiting some changes in volume. The most important of these occurred during the latest Miocene (t = ∼5 m.y. ago) when ice volumes increased beyond those of the present day. This event was related to global climatic cooling, a rapid northward movement of about 300 km of the Antarctic Convergence, and a eustatic sea level drop that may have been partly responsible for the isolation of the Mediterranean basin. Northern hemisphere ice sheet development began about 2.5–3 m.y. ago, representing the next major global climatic threshold, and was followed by the well‐known major oscillations in northern ice sheets. In the Southern Ocean the Quaternary marks a peak in activity of oceanic circulation as reflected by widespread deep‐sea erosion, very high biogenic productivity at the Antarctic Convergence and resulting high rates of biogenic sedimentation, and maximum northward distribution of ice‐rafted debris.",
    url = "https://doi.org/10.1029/jc082i027p03843",
    doi = "10.1029/jc082i027p03843",
    openalex = "W2016564007",
    references = "doi1010160025322771900533, doi1010160025322777900457, doi1010160033589473900525, doi1010160033589476900478, doi101017s0032247400063804, doi101038260513a0, doi101086626295, doi102475ajs2683193, doi102973dsdpproc291171975, doi102973dsdpproc291975"
}

@article{doi1013062f91804f16ce11d78645000102c1865d,
    author = "Thiede, J.",
    title = "Oceans and Climate During Cenozoic: ABSTRACT",
    year = "1979",
    journal = "AAPG Bulletin",
    url = "https://www.semanticscholar.org/paper/9cb0408bda5737d27581c82baf3977fb07e49d83",
    doi = "10.1306/2F91804F-16CE-11D7-8645000102C1865D",
    is_oa = "true",
    semanticscholar_citation_count = "1",
    semanticscholar_id = "9cb0408bda5737d27581c82baf3977fb07e49d83",
    volume = "63"
}

Faunal and lithologic evidence is used to reconstruct paleoceanographic events over the last 4.5 million years. The inception of perennial sea-ice cover is dated at about 0.7 million years.

@article{doi101126science2094456557,
    author = "Herman, Yvonne and Hopkins, David M.",
    title = "Arctic Oceanic Climate in Late Cenozoic Time",
    year = "1980",
    journal = "Science",
    abstract = "Faunal and lithologic evidence is used to reconstruct paleoceanographic events over the last 4.5 million years. The inception of perennial sea-ice cover is dated at about 0.7 million years.",
    url = "https://doi.org/10.1126/science.209.4456.557",
    doi = "10.1126/science.209.4456.557",
    openalex = "W2041936540",
    references = "doi1010160016703773901543, doi101029jc076i006p01550, doi101038270216a0, doi101126science15838041001, doi101126science2024365305, doi101126science2044389173, doi1011300091761319786630pcotio20co2, doi1023071216157, doi1023072412512, openalexw614266484"
}

@misc{herman1980arctic1,
    author = "Herman, Y. and Hopkins, D. M",
    title = "Arctic Ocean climate in late Cenozoic time",
    year = "1980",
    howpublished = "Science, v. 209, p. 557-562",
    note = "talkorigins\_source = {true}; raw\_reference = {Herman, Y., and Hopkins, D. M., 1980, Arctic Ocean climate in late Cenozoic time: Science, v. 209, p. 557-562.}"
}

A brief discussion of, and a little speculation about, the relevance of the polar regions on climate is given. The main body of the paper gives a survey of the known deep convection areas of the world ocean. There are two distinct types of convection. The first is the classic sinking occurring on continental shelf slope systems, as typified by various locations around the Antarctic coast. The freezing of sea ice, and resulting brine ejection, creates dense salty water on the shelf which descends the slope under a balance of Coriolis, gravity, and frictional forces, entraining the surrounding warm deep water as it goes. The second process is the more recently observed open‐ocean convection, occurring in locations such as the Mediterranean, the Labrador Sea, and two locations in the Weddell gyre, and is hypothesized to occur in the Greenland Sea. Open‐ocean convection has many overall similarities in all these areas: it occurs in narrow (20–50 km) areas; it forms about 10 m³ s −l of deep water; it occurs only in regions of cyclonic mean circulation; more than one water mass in the mean circulation is involved; a preconditioning seems to be required; some surface forcing (cooling or sea ice formation) is necessary; a violent breakup of the water mass frequently occurs on time scales of 2 weeks.

@article{doi101029rg021i001p00001,
    author = "Killworth, Peter D.",
    title = "Deep convection in the World Ocean",
    year = "1983",
    journal = "Reviews of Geophysics",
    abstract = "A brief discussion of, and a little speculation about, the relevance of the polar regions on climate is given. The main body of the paper gives a survey of the known deep convection areas of the world ocean. There are two distinct types of convection. The first is the classic sinking occurring on continental shelf slope systems, as typified by various locations around the Antarctic coast. The freezing of sea ice, and resulting brine ejection, creates dense salty water on the shelf which descends the slope under a balance of Coriolis, gravity, and frictional forces, entraining the surrounding warm deep water as it goes. The second process is the more recently observed open‐ocean convection, occurring in locations such as the Mediterranean, the Labrador Sea, and two locations in the Weddell gyre, and is hypothesized to occur in the Greenland Sea. Open‐ocean convection has many overall similarities in all these areas: it occurs in narrow (20–50 km) areas; it forms about 10 m³ s −l of deep water; it occurs only in regions of cyclonic mean circulation; more than one water mass in the mean circulation is involved; a preconditioning seems to be required; some surface forcing (cooling or sea ice formation) is necessary; a violent breakup of the water mass frequently occurs on time scales of 2 weeks.",
    url = "https://doi.org/10.1029/rg021i001p00001",
    doi = "10.1029/rg021i001p00001",
    openalex = "W2072343733"
}

Seasonal changes of the Arctic Ocean are an approximate microcosm of the present advanced interglacial climate of the Earth. A similar relationship has existed for several million years but was the Early Cenozoic Arctic Ocean an analog of Earth's climate, as well. Absence of polar ice during the Cretaceous is relatively well established. During the Cenozoic a worldwide decrease in mean annual ocean temperature resulted from such factors as altered oceanic circulation and lower atmospheric CO/sub 2/ levels. Limited Arctic Ocean data for the middle or late Eocene indicate the presence of upwelling conditions and accompanying high productivity of diatoms, ebridians, silicoflagellates and archaeomonads. During this interval, some seasonality is suggested from the varve-like nature of a single sediment core. However, the absence of drop stones or any ice-rafted sediment supports the idea of an open water, ice-free central Arctic Ocean during this time. Latest Cretaceous Arctic Ocean sediment is interpreted to represent approximately the same conditions as those suggested for the Eocene and together with that data suggest that the central Arctic Ocean was ice-free during part if not all of the first 20 my of the Cenozoic. Sediment representing the succeeding 30 my has not been recovered butmore » by latest Miocene or earl Pliocene, ice-rafted sediment was accumulating, both pack ice and icebergs covered the Arctic Ocean reflecting cyclic glacial climate.« less

@article{s2003bef2ec97b6182da0be87971bdc5d58d72c9cf,
    author = "Clark, D. L.",
    title = "Eocene Arctic Ocean and earth's Early Cenozoic climate",
    year = "1985",
    journal = "Geol. Soc. Am., Abstr. Programs; (United States)",
    abstract = "Seasonal changes of the Arctic Ocean are an approximate microcosm of the present advanced interglacial climate of the Earth. A similar relationship has existed for several million years but was the Early Cenozoic Arctic Ocean an analog of Earth's climate, as well. Absence of polar ice during the Cretaceous is relatively well established. During the Cenozoic a worldwide decrease in mean annual ocean temperature resulted from such factors as altered oceanic circulation and lower atmospheric CO/sub 2/ levels. Limited Arctic Ocean data for the middle or late Eocene indicate the presence of upwelling conditions and accompanying high productivity of diatoms, ebridians, silicoflagellates and archaeomonads. During this interval, some seasonality is suggested from the varve-like nature of a single sediment core. However, the absence of drop stones or any ice-rafted sediment supports the idea of an open water, ice-free central Arctic Ocean during this time. Latest Cretaceous Arctic Ocean sediment is interpreted to represent approximately the same conditions as those suggested for the Eocene and together with that data suggest that the central Arctic Ocean was ice-free during part if not all of the first 20 my of the Cenozoic. Sediment representing the succeeding 30 my has not been recovered butmore » by latest Miocene or earl Pliocene, ice-rafted sediment was accumulating, both pack ice and icebergs covered the Arctic Ocean reflecting cyclic glacial climate.« less",
    url = "https://www.semanticscholar.org/paper/003bef2ec97b6182da0be87971bdc5d58d72c9cf",
    is_oa = "true",
    openalex = "W2238039910",
    semanticscholar_id = "003bef2ec97b6182da0be87971bdc5d58d72c9cf"
}

This study was undertaken in cooperation with David Clark of the University of Wisconsin in order to confirm the previous estimates of low sedimentation rates in the Arctic Basin (see Table 7).

@article{crossref1988arctic,
    title = "Arctic Ocean",
    year = "1988",
    journal = "Radiocarbon",
    abstract = "This study was undertaken in cooperation with David Clark of the University of Wisconsin in order to confirm the previous estimates of low sedimentation rates in the Arctic Basin (see Table 7).",
    url = "https://doi.org/10.1017/s0033822200044301",
    doi = "10.1017/s0033822200044301",
    number = "3",
    pages = "277-277",
    volume = "30"
}

@article{doi1011300091761319880160649iolcmb23co2,
    author = "Raymo, Maureen E. and Ruddiman, William F and Froelich, Philip N.",
    title = "Influence of late Cenozoic mountain building on ocean geochemical cycles",
    year = "1988",
    journal = "Geology",
    url = "https://doi.org/10.1130/0091-7613(1988)016<0649:iolcmb>2.3.co;2",
    doi = "10.1130/0091-7613(1988)016<0649:iolcmb>2.3.co;2",
    openalex = "W1966360142"
}

Geologic evidence indicates that net vertical uplift occurred on a large (kilometer) scale and at accelerating rates during the middle and late Cenozoic in plateaus of southern Asia and the American west. Based on this evidence, General Circulation Model sensitivity tests were run to isolate the unique effects of plateau uplift on climate. The experiments simulated significant climatic changes in many places, some far from the uplifted regions. The basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record: winter cooling of North America, northern Europe, northern Asia, and the Arctic Ocean; summer drying of the North American west coast, the Eurasian interior, and the Mediterranean; winter drying of the North American northern plains and the interior of Asia; and changes over the North Atlantic Ocean conducive to increased formation of deep water. The modeled changes result from increased orographic diversion of westerly winds, from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus, and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer‐heated (and winter‐cooled) plateaus and the mid‐latitude oceans. Disagreements between the geologic record and the model simulations in Alaska and the Southern Rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography. Taken together, the observed regional trends comprise much of the pattern of “late Cenozoic climatic deterioration” in the northern hemisphere that culminated in the Plio‐Pleistocene ice ages. The success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late Cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations; however, the modest amplitude of the uplift‐induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing.

@article{doi101029jd094id15p18409,
    author = "Ruddiman, William F and Kutzbach, John E.",
    title = "Forcing of late Cenozoic northern hemisphere climate by plateau uplift in southern Asia and the American west",
    year = "1989",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Geologic evidence indicates that net vertical uplift occurred on a large (kilometer) scale and at accelerating rates during the middle and late Cenozoic in plateaus of southern Asia and the American west. Based on this evidence, General Circulation Model sensitivity tests were run to isolate the unique effects of plateau uplift on climate. The experiments simulated significant climatic changes in many places, some far from the uplifted regions. The basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record: winter cooling of North America, northern Europe, northern Asia, and the Arctic Ocean; summer drying of the North American west coast, the Eurasian interior, and the Mediterranean; winter drying of the North American northern plains and the interior of Asia; and changes over the North Atlantic Ocean conducive to increased formation of deep water. The modeled changes result from increased orographic diversion of westerly winds, from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus, and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer‐heated (and winter‐cooled) plateaus and the mid‐latitude oceans. Disagreements between the geologic record and the model simulations in Alaska and the Southern Rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography. Taken together, the observed regional trends comprise much of the pattern of “late Cenozoic climatic deterioration” in the northern hemisphere that culminated in the Plio‐Pleistocene ice ages. The success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late Cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations; however, the modest amplitude of the uplift‐induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing.",
    url = "https://doi.org/10.1029/jd094id15p18409",
    doi = "10.1029/jd094id15p18409",
    openalex = "W2052368906",
    references = "crossref194241, doi101007bf02861083, doi1010160012825272900384, doi101029jd089id01p01267, doi101029pa002i001p00001, doi101038300321a0, doi101038307429a0, doi101038334333a0, doi101126science19442701121, doi101126science2094456557, doi101130001676061951621111ghosw20co2, doi1011300091761319880160649iolcmb23co2, doi1011751520046919750321515tromit20co2, doi101357002224083788520207, doi102475ajs2837641, doi102973dsdpproc291171975, doi103402tellusav1i28500"
}

The study of climate and climate change is hindered by a lack of information on the effect of clouds on the radiation balance of the earth, referred to as the cloud-radiative forcing. Quantitative estimates of the global distributions of cloud-radiative forcing have been obtained from the spaceborne Earth Radiation Budget Experiment (ERBE) launched in 1984. For the April 1985 period, the global shortwave cloud forcing [-44.5 watts per square meter (W/m(2))] due to the enhancement of planetary albedo, exceeded in magnitude the longwave cloud forcing (31.3 W/m(2)) resulting from the greenhouse effect of clouds. Thus, clouds had a net cooling effect on the earth. This cooling effect is large over the mid-and high-latitude oceans, with values reaching -100 W/m(2). The monthly averaged longwave cloud forcing reached maximum values of 50 to 100 W/m(2) over the convectively disturbed regions of the tropics. However, this heating effect is nearly canceled by a correspondingly large negative shortwave cloud forcing, which indicates the delicately balanced state of the tropics. The size of the observed net cloud forcing is about four times as large as the expected value of radiative forcing from a doubling of CO(2). The shortwave and longwave components of cloud forcing are about ten times as large as those for a CO(2) doubling. Hence, small changes in the cloud-radiative forcing fields can play a significant role as a climate feedback mechanism. For example, during past glaciations a migration toward the equator of the field of strong, negative cloud-radiative forcing, in response to a similar migration of cooler waters, could have significantly amplified oceanic cooling and continental glaciation.

@article{doi101126science243488757,
    author = "Ramanathan, V. and Cess, R. D. and Harrison, Edwin F. and Minnis, Patrick and Barkstrom, Bruce R. and Ahmad, Ejaz and Hartmann, Dennis L.",
    title = "Cloud-Radiative Forcing and Climate: Results from the Earth Radiation Budget Experiment",
    year = "1989",
    journal = "Science",
    abstract = "The study of climate and climate change is hindered by a lack of information on the effect of clouds on the radiation balance of the earth, referred to as the cloud-radiative forcing. Quantitative estimates of the global distributions of cloud-radiative forcing have been obtained from the spaceborne Earth Radiation Budget Experiment (ERBE) launched in 1984. For the April 1985 period, the global shortwave cloud forcing [-44.5 watts per square meter (W/m(2))] due to the enhancement of planetary albedo, exceeded in magnitude the longwave cloud forcing (31.3 W/m(2)) resulting from the greenhouse effect of clouds. Thus, clouds had a net cooling effect on the earth. This cooling effect is large over the mid-and high-latitude oceans, with values reaching -100 W/m(2). The monthly averaged longwave cloud forcing reached maximum values of 50 to 100 W/m(2) over the convectively disturbed regions of the tropics. However, this heating effect is nearly canceled by a correspondingly large negative shortwave cloud forcing, which indicates the delicately balanced state of the tropics. The size of the observed net cloud forcing is about four times as large as the expected value of radiative forcing from a doubling of CO(2). The shortwave and longwave components of cloud forcing are about ten times as large as those for a CO(2) doubling. Hence, small changes in the cloud-radiative forcing fields can play a significant role as a climate feedback mechanism. For example, during past glaciations a migration toward the equator of the field of strong, negative cloud-radiative forcing, in response to a similar migration of cooler waters, could have significantly amplified oceanic cooling and continental glaciation.",
    url = "https://doi.org/10.1126/science.243.4887.57",
    doi = "10.1126/science.243.4887.57",
    openalex = "W2053811834",
    references = "doi101002qj49711448209, doi101029jd092id11p13315, doi101029rg024i002p00439, doi101038326655a0, doi101038329403a0, doi1011751520046919720291413caagcf20co2, doi1011751520046919760331831ccaaoa20co2, doi1011751520046919800371233otuoer20co2, doi1011751520046919880451397cfpiag20co2, doi1011751520047719840651170terbe20co2"
}

A mathematical model has been constructed that enables calculation of the level of atmospheric O2 over the past 570 my from rates of burial and weathering of organic carbon (C) and pyrite sulfur (S). Burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance, and C and S contents, of the three rock types: marine sandstones and shales, coal basin sediments, and other non-marine clastics (red beds, arkoses). By our model, values of O2 versus time, using a constant total sedimentation rate, agree with those for variable sedimentation derived from present-day rock abundances and estimates of erosional losses since deposition. This agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial, with consequently faster burial of C and S and greater O2 production, must be accompanied by a corresponding increase in erosion and increased exposure of C and S on the continents to O2 consumption via weathering. It is the redistribution of sediment between the three different rock types, and not total sedimentation rate, that is important in O2 control. To add stability to the system, negative feedback against excessive O2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks, resulting in rapid recycling of C and S. We did not use direct O2 negative feedback on either weathering of C and S or burial of C because weathering rates are assumed to be limited by uplift and erosion, and the burial rate of C limited by the rate of sediment deposition. The latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers. Results of the modeling indicate that atmospheric O2 probably has varied appreciably over Phanerozoic time. During the Late Carboniferous and Permian periods O2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps. A large decrease in O2 during the Late Permian was due probably to the drying-up of the coal swamps and deposition of a large proportion of total sediment in C and S-free continental red beds. Sensitivity study shows that major parameters affecting results are the mean C concentration in coal basins and the relative sizes of the reservoirs of young (rapidly recycled) versus old rocks. Less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct O2 negative feedback on marine carbon burial. Good agreement for rates of C burial calculated via our model and via independent models, which are based on the use of stable carbon isotopes, indicates that the dominant factor that has brought about changes in atmospheric O2 level (and the isotopic composition of dissolved inorganic carbon in seawater) over Phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt-seawater reaction.

@article{doi102475ajs2894333,
    author = "Berner, Robert A. and Canfield, Donald E.",
    title = "A new model for atmospheric oxygen over Phanerozoic time",
    year = "1989",
    journal = "American Journal of Science",
    abstract = "A mathematical model has been constructed that enables calculation of the level of atmospheric O2 over the past 570 my from rates of burial and weathering of organic carbon (C) and pyrite sulfur (S). Burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance, and C and S contents, of the three rock types: marine sandstones and shales, coal basin sediments, and other non-marine clastics (red beds, arkoses). By our model, values of O2 versus time, using a constant total sedimentation rate, agree with those for variable sedimentation derived from present-day rock abundances and estimates of erosional losses since deposition. This agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial, with consequently faster burial of C and S and greater O2 production, must be accompanied by a corresponding increase in erosion and increased exposure of C and S on the continents to O2 consumption via weathering. It is the redistribution of sediment between the three different rock types, and not total sedimentation rate, that is important in O2 control. To add stability to the system, negative feedback against excessive O2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks, resulting in rapid recycling of C and S. We did not use direct O2 negative feedback on either weathering of C and S or burial of C because weathering rates are assumed to be limited by uplift and erosion, and the burial rate of C limited by the rate of sediment deposition. The latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers. Results of the modeling indicate that atmospheric O2 probably has varied appreciably over Phanerozoic time. During the Late Carboniferous and Permian periods O2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps. A large decrease in O2 during the Late Permian was due probably to the drying-up of the coal swamps and deposition of a large proportion of total sediment in C and S-free continental red beds. Sensitivity study shows that major parameters affecting results are the mean C concentration in coal basins and the relative sizes of the reservoirs of young (rapidly recycled) versus old rocks. Less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct O2 negative feedback on marine carbon burial. Good agreement for rates of C burial calculated via our model and via independent models, which are based on the use of stable carbon isotopes, indicates that the dominant factor that has brought about changes in atmospheric O2 level (and the isotopic composition of dissolved inorganic carbon in seawater) over Phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt-seawater reaction.",
    url = "https://doi.org/10.2475/ajs.289.4.333",
    doi = "10.2475/ajs.289.4.333",
    openalex = "W1980139183"
}

@article{doi101016002532279090078x,
    author = "Clark, D. L. and Chern, Laura A. and Hogler, J. A. and Mennicke, C. and Atkins, Elizabeth D.",
    title = "Late Neogene climate evolution of the central Arctic Ocean",
    year = "1990",
    journal = "Marine Geology",
    url = "https://www.semanticscholar.org/paper/71e796e9d441a90be91d2543cf7842805b2247e0",
    doi = "10.1016/0025-3227(90)90078-X",
    is_oa = "true",
    pages = "69-94",
    semanticscholar_citation_count = "34",
    semanticscholar_id = "71e796e9d441a90be91d2543cf7842805b2247e0",
    volume = "93"
}

@article{doi101038346029a0,
    author = "Molnár, Péter and England, Philip",
    title = "Late Cenozoic uplift of mountain ranges and global climate change: chicken or egg?",
    year = "1990",
    journal = "Nature",
    url = "https://doi.org/10.1038/346029a0",
    doi = "10.1038/346029a0",
    openalex = "W2045775785",
    references = "doi101017cbo9780511701559, doi101029jd094id15p18409, doi101038329403a0, doi10113000167606196071843peotca20co2, doi1011300091761319880160649iolcmb23co2, doi101146annurevea05050177001535, openalexw623436458"
}

When the Bering Strait between Alaska and Siberia opened about 3.5 Ma during the early Pliocene, cool-temperate and polar marine species were able to move between the North Pacific and Arctic-Atlantic basins. In order to investigate the extent, pattern, and dynamics of this trans-Arctic interchange, I reviewed the Recent and fossil distributions of post-Miocene shell-bearing Mollusca in each of five northern regions: (1) the northeastern Atlantic (Lofoten Islands to the eastern entrance of the English Channel and the northern entrance of the Irish Sea), (2) northwestern Atlantic (southern Labrador to Cape Cod), (3) northeastern Pacific (Bering Strait to Puget Sound), (4) northwestern Pacific (Bering Strait to Hokkaido and the northern Sea of Japan), and (5) Arctic (areas north of the Lofoten Islands, southern Labrador, and Bering Strait). I have identified 295 molluscan species that either took part in the interchange or are descended from taxa that did. Of these, 261 are of Pacific origin, whereas only 34 are of Arctic-Atlantic origin. Various analyses of the pattern of invasion confirm earlier work, indicating that there is a strong bias in favor of species with a Pacific origin. A geographical analysis of invaders implies that, although trans-Arctic interchange contributed to a homogenization of the biotas of the northern oceans, significant barriers to dispersal exist and have existed for trans-Arctic invaders within the Arctic-Atlantic basin. Nevertheless, trans-Arctic invaders in the Atlantic have significantly broader geographical ranges than do taxa with a pre-Pliocene history in the Atlantic. Among the possible explanations for the asymmetry of trans-Arctic invasion, two hypotheses were explicitly tested. The null hypothesis of diversity states that the number of invaders from a biota is proportional to the total number of species in that biota. Estimates of Recent molluscan diversity show that the North Pacific is 1.5 to 2.7 times richer than is the Arctic-Atlantic, depending on how faunistic comparisons are made. This difference in diversity is much smaller than is the asymmetry of trans-Arctic invasion in favor of Pacific species. Rough estimates of regional Pliocene diversity suggest that differences in diversity during the Pliocene were smaller than they are in the Recent fauna. The null hypothesis was therefore rejected. The hypothesis of ecological opportunity states that the number of invaders to a region is proportional to the number of species that became extinct there. The post-Early Pliocene magnitude of extinction was lowest in the North Pacific, intermediate in the northeastern Atlantic, and probably highest in the northwestern Atlantic. The absolute number and faunistic importance of post-Early Pliocene invaders (including trans-Arctic species, as well as taxa previously confined to warm-temperate waters and western Atlantic species that previously occurred only in the eastern Atlantic) was lowest in the North Pacific, intermediate in the northeastern Atlantic, and highest in the northwestern Atlantic. Further support for the hypothesis of ecological opportunity comes from the finding that hard-bottom communities, especially those in the northwestern Atlantic, show a higher representation of molluscan species of Pacific origin, and are likely to have been more affected by climatic events, than were communities on unconsolidated sandy and muddy bottoms. Support for the hypothesis does not rule out other explanations for the observed asymmetry of trans-Arctic invasion. A preliminary study of species-level evolution within lineages of trans-Arctic invaders indicates that anagenesis and cladogenesis have been more frequent among groups with Pacific origins than among those with Atlantic origins, and that the regions within the Arctic-Atlantic basin with the highest absolute number and faunistic representation of invaders (western Atlantic and Arctic) are the regions in which speciation has been least common among the invaders. The asymmetry of invasion is therefore distinct from the asymmetry of species-level evolution of invaders in the various northern marine regions.

@article{doi101017s0094837300010617,
    author = "Vermeij, Geerat J.",
    title = "Anatomy of an invasion: the trans-Arctic interchange",
    year = "1991",
    journal = "Paleobiology",
    abstract = "When the Bering Strait between Alaska and Siberia opened about 3.5 Ma during the early Pliocene, cool-temperate and polar marine species were able to move between the North Pacific and Arctic-Atlantic basins. In order to investigate the extent, pattern, and dynamics of this trans-Arctic interchange, I reviewed the Recent and fossil distributions of post-Miocene shell-bearing Mollusca in each of five northern regions: (1) the northeastern Atlantic (Lofoten Islands to the eastern entrance of the English Channel and the northern entrance of the Irish Sea), (2) northwestern Atlantic (southern Labrador to Cape Cod), (3) northeastern Pacific (Bering Strait to Puget Sound), (4) northwestern Pacific (Bering Strait to Hokkaido and the northern Sea of Japan), and (5) Arctic (areas north of the Lofoten Islands, southern Labrador, and Bering Strait). I have identified 295 molluscan species that either took part in the interchange or are descended from taxa that did. Of these, 261 are of Pacific origin, whereas only 34 are of Arctic-Atlantic origin. Various analyses of the pattern of invasion confirm earlier work, indicating that there is a strong bias in favor of species with a Pacific origin. A geographical analysis of invaders implies that, although trans-Arctic interchange contributed to a homogenization of the biotas of the northern oceans, significant barriers to dispersal exist and have existed for trans-Arctic invaders within the Arctic-Atlantic basin. Nevertheless, trans-Arctic invaders in the Atlantic have significantly broader geographical ranges than do taxa with a pre-Pliocene history in the Atlantic. Among the possible explanations for the asymmetry of trans-Arctic invasion, two hypotheses were explicitly tested. The null hypothesis of diversity states that the number of invaders from a biota is proportional to the total number of species in that biota. Estimates of Recent molluscan diversity show that the North Pacific is 1.5 to 2.7 times richer than is the Arctic-Atlantic, depending on how faunistic comparisons are made. This difference in diversity is much smaller than is the asymmetry of trans-Arctic invasion in favor of Pacific species. Rough estimates of regional Pliocene diversity suggest that differences in diversity during the Pliocene were smaller than they are in the Recent fauna. The null hypothesis was therefore rejected. The hypothesis of ecological opportunity states that the number of invaders to a region is proportional to the number of species that became extinct there. The post-Early Pliocene magnitude of extinction was lowest in the North Pacific, intermediate in the northeastern Atlantic, and probably highest in the northwestern Atlantic. The absolute number and faunistic importance of post-Early Pliocene invaders (including trans-Arctic species, as well as taxa previously confined to warm-temperate waters and western Atlantic species that previously occurred only in the eastern Atlantic) was lowest in the North Pacific, intermediate in the northeastern Atlantic, and highest in the northwestern Atlantic. Further support for the hypothesis of ecological opportunity comes from the finding that hard-bottom communities, especially those in the northwestern Atlantic, show a higher representation of molluscan species of Pacific origin, and are likely to have been more affected by climatic events, than were communities on unconsolidated sandy and muddy bottoms. Support for the hypothesis does not rule out other explanations for the observed asymmetry of trans-Arctic invasion. A preliminary study of species-level evolution within lineages of trans-Arctic invaders indicates that anagenesis and cladogenesis have been more frequent among groups with Pacific origins than among those with Atlantic origins, and that the regions within the Arctic-Atlantic basin with the highest absolute number and faunistic representation of invaders (western Atlantic and Arctic) are the regions in which speciation has been least common among the invaders. The asymmetry of invasion is therefore distinct from the asymmetry of species-level evolution of invaders in the various northern marine regions.",
    url = "https://doi.org/10.1017/s0094837300010617",
    doi = "10.1017/s0094837300010617",
    openalex = "W2265541152",
    references = "darlington1959area, doi10108011035898309454564, doi101093aibsbulletin3217e, doi101126science2094456557, doi101126science6771870, doi1015159780691224244, doi1023073544109, doi105962bhltitle59991, doi105962bhltitle61718, openalexw1528487914, openalexw1548779714, openalexw657543899"
}

A new model has been constructed for calculating the level of atmospheric CO{sub 2} over Phanerozoic time which is much simpler mathematically than the BLAG model, but more complex geologically and biologically. Results suggest that there has been a notable pattern of varying atmospheric CO{sub 2} level over the past 570 my with high levels during the Mesozoic and early Paleozoic and low levels during the Permo-Carboniferous and late Cenozoic. Sensitivity analysis shows that, within reasonable limits of the principal governing parameters, this qualitative trend of varying CO{sub 2} is relatively insensitive to the actual values chosen for these parameters. Causes of the CO{sub 2} variation are multiple, and no single geological or biological process can be called upon to explain all CO{sub 2} variation for all time. The calculated trend of CO{sub 2} over time agrees well with independent estimations of paleoclimates. Thus, the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study.

@article{doi102475ajs2914339,
    author = "Berner, Robert A.",
    title = "A model for atmospheric CO 2 over Phanerozoic time",
    year = "1991",
    journal = "American Journal of Science",
    abstract = "A new model has been constructed for calculating the level of atmospheric CO{sub 2} over Phanerozoic time which is much simpler mathematically than the BLAG model, but more complex geologically and biologically. Results suggest that there has been a notable pattern of varying atmospheric CO{sub 2} level over the past 570 my with high levels during the Mesozoic and early Paleozoic and low levels during the Permo-Carboniferous and late Cenozoic. Sensitivity analysis shows that, within reasonable limits of the principal governing parameters, this qualitative trend of varying CO{sub 2} is relatively insensitive to the actual values chosen for these parameters. Causes of the CO{sub 2} variation are multiple, and no single geological or biological process can be called upon to explain all CO{sub 2} variation for all time. The calculated trend of CO{sub 2} over time agrees well with independent estimations of paleoclimates. Thus, the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study.",
    url = "https://doi.org/10.2475/ajs.291.4.339",
    doi = "10.2475/ajs.291.4.339",
    openalex = "W2030169181"
}

We have constructed a magnetic polarity time scale for the Late Cretaceous and Cenozoic based on an analysis of marine magnetic profiles from the world's ocean basins. This is the first time, since Heirtzler et al. (1968) published their time scale, that the relative widths of the magnetic polarity intervals for the entire Late Cretaceous and Cenozoic have been systematically determined from magnetic profiles. A composite geomagnetic polarity sequence was derived based primarily on data from the South Atlantic. Anomaly spacings in the South Atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles. Fine‐scale information was derived from magnetic profiles on faster spreading ridges in the Pacific and Indian Oceans and inserted into the South Atlantic sequence. Based on the assumption that spreading rates in the South Atlantic were smoothly varying but not necessarily constant, a time scale was generated by using a spline function to fit a set of nine age calibration points plus the zero‐age ridge axis to the composite polarity sequence. The derived spreading history of the South Atlantic shows a regular variation in spreading rate, decreasing in the Late Cretaceous from a high of almost 70 mm/yr (full rate) at around anomaly 33–34 time to a low of about 30 mm/yr by anomaly 27 time in the early Paleocene, increasing to about 55 mm/yr by about anomaly 15 time in the late Eocene, and then gradually decreasing over the Oligocene and the Neogene to the recent rate of about 32 mm/yr. The new time scale has several significant differences from previous time scales. For example, chron C5n is ∼0.5 m.y. older and chrons C9 through C24 are 2–3 m.y. younger than in the chronologies of Berggren et al. (1985b) and Harland et al. (1990). Additional small‐scale anomalies (tiny wiggles) that represent either very short polarity intervals or intensity fluctuations of the dipole field have been identified from several intervals in the Cenozoic including a large number of tiny wiggles between anomalies 24 and 27. Spreading rates on several other ridges, including the Southeast Indian Ridge, the East Pacific Rise, the Pacific‐Antarctic Ridge, the Chile Ridge, the North Pacific, and the Central Atlantic, were analyzed in order to evaluate the accuracy of the new time scale. Globally synchronous variations in spreading rate that were previously observed around anomalies 20, 6C, and in the late Neogene have been eliminated. The new time scale helps to resolve events at the times of major plate reorganizations. For example, anomaly 3A (5.6 Ma) is now seen to be a time of sudden spreading rate changes in the Southeast Indian, Pacific‐Antarctic, and Chile ridges and may correspond to the time of the change in Pacific absolute plate motion proposed by others. Spreading rates in the North Pacific became increasingly irregular in the Oligocene, culminating in a precipitous drop at anomaly 6C time.

@article{doi10102992jb01202,
    author = "Cande, S. C. and Kent, Dennis V.",
    title = "A new geomagnetic polarity time scale for the Late Cretaceous and Cenozoic",
    year = "1992",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "We have constructed a magnetic polarity time scale for the Late Cretaceous and Cenozoic based on an analysis of marine magnetic profiles from the world's ocean basins. This is the first time, since Heirtzler et al. (1968) published their time scale, that the relative widths of the magnetic polarity intervals for the entire Late Cretaceous and Cenozoic have been systematically determined from magnetic profiles. A composite geomagnetic polarity sequence was derived based primarily on data from the South Atlantic. Anomaly spacings in the South Atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles. Fine‐scale information was derived from magnetic profiles on faster spreading ridges in the Pacific and Indian Oceans and inserted into the South Atlantic sequence. Based on the assumption that spreading rates in the South Atlantic were smoothly varying but not necessarily constant, a time scale was generated by using a spline function to fit a set of nine age calibration points plus the zero‐age ridge axis to the composite polarity sequence. The derived spreading history of the South Atlantic shows a regular variation in spreading rate, decreasing in the Late Cretaceous from a high of almost 70 mm/yr (full rate) at around anomaly 33–34 time to a low of about 30 mm/yr by anomaly 27 time in the early Paleocene, increasing to about 55 mm/yr by about anomaly 15 time in the late Eocene, and then gradually decreasing over the Oligocene and the Neogene to the recent rate of about 32 mm/yr. The new time scale has several significant differences from previous time scales. For example, chron C5n is ∼0.5 m.y. older and chrons C9 through C24 are 2–3 m.y. younger than in the chronologies of Berggren et al. (1985b) and Harland et al. (1990). Additional small‐scale anomalies (tiny wiggles) that represent either very short polarity intervals or intensity fluctuations of the dipole field have been identified from several intervals in the Cenozoic including a large number of tiny wiggles between anomalies 24 and 27. Spreading rates on several other ridges, including the Southeast Indian Ridge, the East Pacific Rise, the Pacific‐Antarctic Ridge, the Chile Ridge, the North Pacific, and the Central Atlantic, were analyzed in order to evaluate the accuracy of the new time scale. Globally synchronous variations in spreading rate that were previously observed around anomalies 20, 6C, and in the late Neogene have been eliminated. The new time scale helps to resolve events at the times of major plate reorganizations. For example, anomaly 3A (5.6 Ma) is now seen to be a time of sudden spreading rate changes in the Southeast Indian, Pacific‐Antarctic, and Chile ridges and may correspond to the time of the change in Pacific absolute plate motion proposed by others. Spreading rates in the North Pacific became increasingly irregular in the Oligocene, culminating in a precipitous drop at anomaly 6C time.",
    url = "https://doi.org/10.1029/92jb01202",
    doi = "10.1029/92jb01202",
    openalex = "W2096557357",
    references = "doi1010160012821x9190206w, doi101017s0263593300020782, doi101029jb073i006p02119, doi101029jb083ib11p05331, doi101029jb084ib02p00615, doi101038199947a0, doi101126science15437531164, doi10113000167606197788367ucmsag20co2, doi10113000167606197788374ucmsag20co2, doi10113000167606197788383ucmsag20co2, doi101130001676061985961407cg20co2, doi101130dnaggnam351, doi101144gslmem19850100115, doi1015159781400862924, doi102110pec88010071, openalexw2989049194, openalexw638747108"
}

@article{doi101038359117a0,
    author = "Raymo, Maureen E. and Ruddiman, William F",
    title = "Tectonic forcing of late Cenozoic climate",
    year = "1992",
    journal = "Nature",
    url = "https://doi.org/10.1038/359117a0",
    doi = "10.1038/359117a0",
    openalex = "W1999924690",
    references = "doi101017cbo9780511701559, doi101029jd094id15p18409, doi101029pa002i001p00001, doi101038329408a0, doi101126science25550521663, doi10113000917613198210516vosstp20co2, doi1011300091761319880160649iolcmb23co2, doi102475ajs2837641, openalexw1552913007"
}

Detailed investigations of high latitude sequences recently collected by the Ocean Drilling Program (ODP) indicate that periods of rapid climate change often culminated in brief transient climates, with more extreme conditions than subsequent long term climates. Two examples of such events have been identified in the Paleogene; the first in latest Paleocene time in the middle of a warming trend that began several million years earlier: the second in earliest Oligocene time near the end of a Middle Eocene to Late Oligocene global cooling trend. Superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters. Imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice-sheet on Antarctica. In both cases the climate extremes were not stable, lasting for less than a few hundred thousand years, indicating a temporary or transient climate state. Geochemical and sedimentological evidence suggest that both Paleogene climate events were accompanied by reorganizations in ocean circulation, and major perturbations in marine productivity and the global carbon cycle. The Paleocene-Eocene thermal maximum was marked by reduced oceanic turnover and decreases in global delta 13C and in marine productivity, while the Early Oligocene glacial maximum was accompanied by intensification of deep ocean circulation and elevated delta 13C and productivity. It has been suggested that sudden changes in climate and/or ocean circulation might occur as a result of gradual forcing as certain physical thresholds are exceeded. We investigate the possibility that sudden reorganizations in ocean and/or atmosphere circulation during these abrupt transitions generated short-term positive feedbacks that briefly sustained these transient climatic states.

@article{doi101086648216,
    author = "Zachos, James C. and Lohmann, Kyger C. and Walker, James C. G. and Wise, Sherwood W",
    title = "Abrupt Climate Change and Transient Climates during the Paleogene: A Marine Perspective",
    year = "1993",
    journal = "The Journal of Geology",
    abstract = "Detailed investigations of high latitude sequences recently collected by the Ocean Drilling Program (ODP) indicate that periods of rapid climate change often culminated in brief transient climates, with more extreme conditions than subsequent long term climates. Two examples of such events have been identified in the Paleogene; the first in latest Paleocene time in the middle of a warming trend that began several million years earlier: the second in earliest Oligocene time near the end of a Middle Eocene to Late Oligocene global cooling trend. Superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters. Imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice-sheet on Antarctica. In both cases the climate extremes were not stable, lasting for less than a few hundred thousand years, indicating a temporary or transient climate state. Geochemical and sedimentological evidence suggest that both Paleogene climate events were accompanied by reorganizations in ocean circulation, and major perturbations in marine productivity and the global carbon cycle. The Paleocene-Eocene thermal maximum was marked by reduced oceanic turnover and decreases in global delta 13C and in marine productivity, while the Early Oligocene glacial maximum was accompanied by intensification of deep ocean circulation and elevated delta 13C and productivity. It has been suggested that sudden changes in climate and/or ocean circulation might occur as a result of gradual forcing as certain physical thresholds are exceeded. We investigate the possibility that sudden reorganizations in ocean and/or atmosphere circulation during these abrupt transitions generated short-term positive feedbacks that briefly sustained these transient climatic states.",
    url = "https://doi.org/10.1086/648216",
    doi = "10.1086/648216",
    openalex = "W2015218318",
    references = "doi1010160031018284900373, doi101029pa002i003p00287, doi10113000917613198412287cmsaiv20co2, doi1011300091761319920200569eoiseo23co2, doi10151597814008629241, doi1015159781400862924131, doi102973odpprocsr1192001991"
}

Numerous climate models predict that the geography of the supercontinent Pangea was conducive to the establishment of a "megamonsoonal" circulation. In general, geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the Triassic. Pangea in the Late Carboniferous had widespread peat formation in what is now central and eastern North America and Europe and relatively dry conditions on the Colorado Plateau. The equatorial region of the continent became drier through the end of the Carboniferous. By the Permian, the equatorial region of Pangea was dry, and indicators of aridity and rainfall seasonality became more widespread. Wind directions from Colorado Plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time. In the Triassic, climate in the Colorado Plateau region became relatively wet, though still seasonal, and the few eolian sandstones indicate a major shift in wind direction at that time. In addition, sedimentation in Australia, which was in relatively high latitudes, took on a much drier and more seasonal character. These two events support the hypothesis that the Pangean monsoon was at maximum strength during the Triassic. In the Early Jurassic, the Colorado Plateau region became arid again, but climate apparently became wetter in eastern Laurussia and Gondwana. Finally, drying occurred in Gondwana and southern Laurasia, indicative of the breakdown of the Pangean monsoon.

@article{doi101086648217,
    author = "Parrish, Judith Totman",
    title = "Climate of the Supercontinent Pangea",
    year = "1993",
    journal = "The Journal of Geology",
    abstract = {Numerous climate models predict that the geography of the supercontinent Pangea was conducive to the establishment of a "megamonsoonal" circulation. In general, geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the Triassic. Pangea in the Late Carboniferous had widespread peat formation in what is now central and eastern North America and Europe and relatively dry conditions on the Colorado Plateau. The equatorial region of the continent became drier through the end of the Carboniferous. By the Permian, the equatorial region of Pangea was dry, and indicators of aridity and rainfall seasonality became more widespread. Wind directions from Colorado Plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time. In the Triassic, climate in the Colorado Plateau region became relatively wet, though still seasonal, and the few eolian sandstones indicate a major shift in wind direction at that time. In addition, sedimentation in Australia, which was in relatively high latitudes, took on a much drier and more seasonal character. These two events support the hypothesis that the Pangean monsoon was at maximum strength during the Triassic. In the Early Jurassic, the Colorado Plateau region became arid again, but climate apparently became wetter in eastern Laurussia and Gondwana. Finally, drying occurred in Gondwana and southern Laurasia, indicative of the breakdown of the Pangean monsoon.},
    url = "https://doi.org/10.1086/648217",
    doi = "10.1086/648217",
    openalex = "W2043165162",
    references = "crossref1977mesozoic, doi1010079783642688362, doi101007978364268836217, doi1010160012825277901362, doi1010160031018284900944, doi1010160031018285900562, doi1010160037073884900745, doi1010160037073888900565, doi10102991jb00336, doi101029jd094id03p03341, doi101038228657a0, doi101038279590a0, doi101086628416, doi101126science24949751382, doi10113000167606196778353forbim20co2, doi10113000167606198798475lpgeig20co2, doi1011300091761319900180533pcosro23co2, doi101144gsjgs14720321, doi101144gslmem19900120105, doi1011751520046919750321515tromit20co2, doi102110scn8415, doi1023071445584, doi1023073514963, openalexw1504637003, openalexw1539997818"
}

The equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals: late Paleocene, early Eocene, early middle Eocene, late Eocene, and early Oligocene. Paleotemperatures are calculated using standard oxygen isotope/temperature equations with adjustments to account for (1) variations in sea water δ 18 O related to changes in global ice volume over time and (2) latitudinal gradients in surface water δ 18 O. These reconstructions indicate that sea‐surface temperatures (SST) of the Southern Oceans in the early Eocene were as high as 15°C, whereas temperatures during the late Paleocene and early middle Eocene reached maximum levels of 10°–12°C. By the late Eocene and early Oligocene high latitude SST had declined to 6 and 4°C, respectively. For most of the early Paleogene, low latitude sub‐tropical temperatures remained constant and well within the range of Holocene temperatures (24°ndash;25°C) but by the late Eocene and early Oligocene declined to values in the range of 18° to 22°C. The late Paleogene apparent decline in tropical temperatures, however, might be artificial because of dissolution of near‐surface foraminifera tests which biased sediment assemblages toward deeper‐dwelling foraminifera. Moreover, according to recent plate reconstructions, it appears that the majority of sites upon which the late Eocene and early Oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling. Global deepwater temperature on average paralleled southern ocean SST for most of the Paleogene. We speculate based on the overall timing and character of marine sea surface temperature variation during the Paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high‐latitude warmth of the early Eocene.

@article{doi10102993pa03266,
    author = "Zachos, James C. and Stott, Lowell and Lohmann, Kyger C.",
    title = "Evolution of Early Cenozoic marine temperatures",
    year = "1994",
    journal = "Paleoceanography",
    abstract = "The equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals: late Paleocene, early Eocene, early middle Eocene, late Eocene, and early Oligocene. Paleotemperatures are calculated using standard oxygen isotope/temperature equations with adjustments to account for (1) variations in sea water δ 18 O related to changes in global ice volume over time and (2) latitudinal gradients in surface water δ 18 O. These reconstructions indicate that sea‐surface temperatures (SST) of the Southern Oceans in the early Eocene were as high as 15°C, whereas temperatures during the late Paleocene and early middle Eocene reached maximum levels of 10°–12°C. By the late Eocene and early Oligocene high latitude SST had declined to 6 and 4°C, respectively. For most of the early Paleogene, low latitude sub‐tropical temperatures remained constant and well within the range of Holocene temperatures (24°ndash;25°C) but by the late Eocene and early Oligocene declined to values in the range of 18° to 22°C. The late Paleogene apparent decline in tropical temperatures, however, might be artificial because of dissolution of near‐surface foraminifera tests which biased sediment assemblages toward deeper‐dwelling foraminifera. Moreover, according to recent plate reconstructions, it appears that the majority of sites upon which the late Eocene and early Oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling. Global deepwater temperature on average paralleled southern ocean SST for most of the Paleogene. We speculate based on the overall timing and character of marine sea surface temperature variation during the Paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high‐latitude warmth of the early Eocene.",
    url = "https://doi.org/10.1029/93pa03266",
    doi = "10.1029/93pa03266",
    openalex = "W2126248410",
    references = "doi1010160016703788901329, doi1010160016703789902834, doi1010160031018284900373, doi101016003101829290096n, doi1010160198014985900172, doi10102992jb01202, doi101029jc082i027p03843, doi101029pa002i001p00001, doi101029pa002i003p00287, doi101038353225a0, doi101086626295, doi101126science243488757, doi10113000917613198412287cmsaiv20co2, doi1011300091761319920200569eoiseo23co2, doi101146annurevea05050177001535, doi102475ajs2914339, doi102973dsdpproc291171975, doi102973odpprocsr1192001991"
}

The northern North Atlantic sediment drifts have a much greater areal extent than has previously been indicated. The northern North Atlantic extends from the East Greenland to European continental shelves and from the Charlie‐Gibbs Fracture Zone to the Greenland‐Scotland Ridge. Within this region are seven major sediment drifts containing some of the best clues for pre‐Quaternary bottom water circulation in the North Atlantic. Feni Drift is the oldest in the region, originating near the Eocene‐Oligocene boundary. It was followed by accumulation of Bjorn, Gardar, Hatton, and Snorri Drifts from the late Early to Middle Miocene. Eirik Drift may have started to accumulate in the Late Miocene, and Gloria Drift in the Early Pliocene. Through analysis of the Cenozoic sediment mass/age distribution and the change in area of seafloor for the study area through time, it can be concluded that there is a deficit of Oligocene to Miocene sediment in the region. This could be explained by sediment cycling; the erosion of older sediment to produce young sediment. The mass of Pliocene to Quaternary sediment is much larger than that of the older sediment and may have been derived primarily through the erosion of Eocene and Oligocene sediment by deepwater currents. The sediment drift portion of the total regional sediment mass, increased significantly three times during the Cenozoic. Each of these drift growth phases, lasted between 3 and 4 m.y. The first two growth phases, from the Late Eocene to Early Oligocene and from the Early to Middle Miocene, were accompanied by northward shifts of depocenters to the newly forming sediment drifts. The third and largest growth phase occurred between 7 and 3 Ma, and may have been preceded by the initiation of accumulation on Eirik Drift, 8–7 Ma. This most recent growth phase was accompanied by high apparent accumulation rates over southern Gardar Drift as it expanded to the east. Erosion rates over Reykjanes Ridge may have been higher during the mid‐Pliocene than in the Quaternary. There are two main sites where dense water could have formed and flowed south through the Rockall Trough to start the accumulation of Feni Drift. If the atmosphere were cool enough, dense water could have formed in the Norwegian Sea or on the Faeroe Shelf. Dense water may also have formed on the Rockall Plateau due to salinity increase through evaporation in an arid climate. As an alternative to the hypothesis of Arctic Ocean water overflowing the Iceland‐Faeroe Ridge in the early‐middle Miocene, it is suggested that dense water formed along shallow segments of the Iceland‐Faeroe Ridge and then flowed into the South Iceland Basin to begin accumulation of Bjorn, Gardar and Snorri Drifts. The initiation of sediment drift formation in the South Iceland Basin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a Middle Miocene uplift event along the Iceland‐Faeroe Ridge. A second uplift event along the Greenland‐Scotland Ridge and a decreased production of Northern Component Water in the early Pliocene may be responsible for increased sediment accumulation in Bjorn, Gardar and Eirik Drifts.

@article{doi10102994pa01438,
    author = "Wold, Christopher N.",
    title = "Cenozoic sediment accumulation on drifts in the northern North Atlantic",
    year = "1994",
    journal = "Paleoceanography",
    abstract = "The northern North Atlantic sediment drifts have a much greater areal extent than has previously been indicated. The northern North Atlantic extends from the East Greenland to European continental shelves and from the Charlie‐Gibbs Fracture Zone to the Greenland‐Scotland Ridge. Within this region are seven major sediment drifts containing some of the best clues for pre‐Quaternary bottom water circulation in the North Atlantic. Feni Drift is the oldest in the region, originating near the Eocene‐Oligocene boundary. It was followed by accumulation of Bjorn, Gardar, Hatton, and Snorri Drifts from the late Early to Middle Miocene. Eirik Drift may have started to accumulate in the Late Miocene, and Gloria Drift in the Early Pliocene. Through analysis of the Cenozoic sediment mass/age distribution and the change in area of seafloor for the study area through time, it can be concluded that there is a deficit of Oligocene to Miocene sediment in the region. This could be explained by sediment cycling; the erosion of older sediment to produce young sediment. The mass of Pliocene to Quaternary sediment is much larger than that of the older sediment and may have been derived primarily through the erosion of Eocene and Oligocene sediment by deepwater currents. The sediment drift portion of the total regional sediment mass, increased significantly three times during the Cenozoic. Each of these drift growth phases, lasted between 3 and 4 m.y. The first two growth phases, from the Late Eocene to Early Oligocene and from the Early to Middle Miocene, were accompanied by northward shifts of depocenters to the newly forming sediment drifts. The third and largest growth phase occurred between 7 and 3 Ma, and may have been preceded by the initiation of accumulation on Eirik Drift, 8–7 Ma. This most recent growth phase was accompanied by high apparent accumulation rates over southern Gardar Drift as it expanded to the east. Erosion rates over Reykjanes Ridge may have been higher during the mid‐Pliocene than in the Quaternary. There are two main sites where dense water could have formed and flowed south through the Rockall Trough to start the accumulation of Feni Drift. If the atmosphere were cool enough, dense water could have formed in the Norwegian Sea or on the Faeroe Shelf. Dense water may also have formed on the Rockall Plateau due to salinity increase through evaporation in an arid climate. As an alternative to the hypothesis of Arctic Ocean water overflowing the Iceland‐Faeroe Ridge in the early‐middle Miocene, it is suggested that dense water formed along shallow segments of the Iceland‐Faeroe Ridge and then flowed into the South Iceland Basin to begin accumulation of Bjorn, Gardar and Snorri Drifts. The initiation of sediment drift formation in the South Iceland Basin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a Middle Miocene uplift event along the Iceland‐Faeroe Ridge. A second uplift event along the Greenland‐Scotland Ridge and a decreased production of Northern Component Water in the early Pliocene may be responsible for increased sediment accumulation in Bjorn, Gardar and Eirik Drifts.",
    url = "https://doi.org/10.1029/94pa01438",
    doi = "10.1029/94pa01438",
    openalex = "W1971456699",
    references = "doi1010160025322771900533, doi1010160198014981901229, doi1010160967065393900242, doi10102990eo00319, doi101029jb085ib07p03711, doi101029rg021i001p00001, doi10108800319112331031, doi10113000167606197788969eotns20co2, doi101306m43478, doi1023073060311"
}

Revision of the GEOCARB model (Berner, 1991, 1994) for paleolevels of atmospheric CO2, has been made with emphasis on factors affecting CO2 uptake by continental weathering. This includes: (1) new GCM (general circulation model) results for the dependence of global mean surface temperature and runoff on CO2, for both glaciated and non-glaciated periods, coupled with new results for the temperature response to changes in solar radiation; (2) demonstration that values for the weathering-uplift factor fR(t) based on Sr isotopes as was done in GEOCARB II are in general agreement with independent values calculated from the abundance of terrigenous sediments as a measure of global physical erosion rate over Phanerozoic time; (3) more accurate estimates of the timing and the quantitative effects on Ca-Mg silicate weathering of the rise of large vascular plants on the continents during the Devonian; (4) inclusion of the effects of changes in paleogeography alone (constant CO2 and solar radiation) on global mean land surface temperature as it affects the rate of weathering; (5) consideration of the effects of volcanic weathering, both in subduction zones and on the seafloor; (6) use of new data on the d 13 C values for Phanerozoic limestones and organic matter; (7) consideration of the relative weather- ing enhancement by gymnosperms versus angiosperms; (8) revision of paleo land area based on more recent data and use of this data, along with GCM-based paleo-runoff results, to calculate global water discharge from the continents over time. Results show a similar overall pattern to those for GEOCARB II: very high CO2 values during the early Paleozoic, a large drop during the Devonian and Carbonifer- ous, high values during the early Mesozoic, and a gradual decrease from about 170 Ma to low values during the Cenozoic. However, the new results exhibit considerably higher CO2 values during the Mesozoic, and their downward trend with time agrees with the independent estimates of Ekart and others (1999). Sensitivity analysis shows that results for paleo-CO2 are especially sensitive to: the effects of CO2 fertilization and temperature on the acceleration of plant-mediated chemical weathering; the quantitative effects of plants on mineral dissolution rate for constant temperature and CO2; the relative roles of angiosperms and gymnosperms in accelerating rock weather- ing; and the response of paleo-temperature to the global climate model used. This emphasizes the need for further study of the role of plants in chemical weathering and the application of GCMs to study of paleo-CO2 and the long term carbon cycle.

@article{doi102475ajs294156,
    author = "Berner, Robert A.",
    title = "GEOCARB II; a revised model of atmospheric CO 2 over Phanerozoic time",
    year = "1994",
    journal = "American Journal of Science",
    abstract = "Revision of the GEOCARB model (Berner, 1991, 1994) for paleolevels of atmospheric CO2, has been made with emphasis on factors affecting CO2 uptake by continental weathering. This includes: (1) new GCM (general circulation model) results for the dependence of global mean surface temperature and runoff on CO2, for both glaciated and non-glaciated periods, coupled with new results for the temperature response to changes in solar radiation; (2) demonstration that values for the weathering-uplift factor fR(t) based on Sr isotopes as was done in GEOCARB II are in general agreement with independent values calculated from the abundance of terrigenous sediments as a measure of global physical erosion rate over Phanerozoic time; (3) more accurate estimates of the timing and the quantitative effects on Ca-Mg silicate weathering of the rise of large vascular plants on the continents during the Devonian; (4) inclusion of the effects of changes in paleogeography alone (constant CO2 and solar radiation) on global mean land surface temperature as it affects the rate of weathering; (5) consideration of the effects of volcanic weathering, both in subduction zones and on the seafloor; (6) use of new data on the d 13 C values for Phanerozoic limestones and organic matter; (7) consideration of the relative weather- ing enhancement by gymnosperms versus angiosperms; (8) revision of paleo land area based on more recent data and use of this data, along with GCM-based paleo-runoff results, to calculate global water discharge from the continents over time. Results show a similar overall pattern to those for GEOCARB II: very high CO2 values during the early Paleozoic, a large drop during the Devonian and Carbonifer- ous, high values during the early Mesozoic, and a gradual decrease from about 170 Ma to low values during the Cenozoic. However, the new results exhibit considerably higher CO2 values during the Mesozoic, and their downward trend with time agrees with the independent estimates of Ekart and others (1999). Sensitivity analysis shows that results for paleo-CO2 are especially sensitive to: the effects of CO2 fertilization and temperature on the acceleration of plant-mediated chemical weathering; the quantitative effects of plants on mineral dissolution rate for constant temperature and CO2; the relative roles of angiosperms and gymnosperms in accelerating rock weather- ing; and the response of paleo-temperature to the global climate model used. This emphasizes the need for further study of the role of plants in chemical weathering and the application of GCMs to study of paleo-CO2 and the long term carbon cycle.",
    url = "https://doi.org/10.2475/ajs.294.1.56",
    doi = "10.2475/ajs.294.1.56",
    openalex = "W2107127140",
    references = "doi101006anbo19951112, doi1010160012821x9290070c, doi101038340457a0, doi10106313067687, doi1011300091761319910190344gestcc23co2, doi1011300091761319910190547lpoeef23co2, doi101146annureves21110190001123, doi102475ajs2914339, doi102475ajs2947802, openalexw1564144063"
}

Recently reported radioisotopic dates and magnetic anomaly spacings have made it evident that modification is required for the age calibrations for the geomagnetic polarity timescale of Cande and Kent (1992) at the Cretaceous/Paleogene boundary and in the Pliocene. An adjusted geomagnetic reversal chronology for the Late Cretaceous and Cenozoic is presented that is consistent with astrochronology in the Pleistocene and Pliocene and with a new timescale for the Mesozoic.

@article{doi10102994jb03098,
    author = "Cande, S. C. and Kent, Dennis V.",
    title = "Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic",
    year = "1995",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Recently reported radioisotopic dates and magnetic anomaly spacings have made it evident that modification is required for the age calibrations for the geomagnetic polarity timescale of Cande and Kent (1992) at the Cretaceous/Paleogene boundary and in the Pliocene. An adjusted geomagnetic reversal chronology for the Late Cretaceous and Cenozoic is presented that is consistent with astrochronology in the Pleistocene and Pliocene and with a new timescale for the Mesozoic.",
    url = "https://doi.org/10.1029/94jb03098",
    doi = "10.1029/94jb03098",
    openalex = "W2108316127",
    references = "doi1010160012821x9190082s, doi101017s0263593300020782, doi10102992jb01202, doi10102993gl00733, doi10102994jb01889, doi101038364788a0, doi101086629744, doi101126science2575072954, doi1011300091761319940220783ioaart23co2, doi101139e93174"
}

Since the publication of our previous time scale (Berggren and others, 1985c = BKFV85) a large amount of new magneto- and biostratigraphic data and radioisotopic ages have become available. An evaluation of some of the key magnetobiostratigraphic calibration points used in BKFV85, as suggested by high precision 40 Ar/ 39 Ar dating (e.g., Montanari and others, 1988; Swisher and Prothero, 1990; Prothero and Swisher, 1992; Prothero, 1994), has served as a catalyst for us in developing a revised Cenozoic time scale. For the Neogene Period, astrochron- ologic data (Shackleton and others, 1990; Hilgen, 1991) required re-evaluation of the calibration of the Pliocene and Pleistocene Epochs. The significantly older ages for the Pliocene-Pleistocene Epochs predicted by astronomical calibrations were soon corroborated by high precision 40 Ar/ 39 Ar dating (e.g., Baksi and others, 1992; McDougall and others, 1992; Tauxe and others, 1992; Walter and others, 1991; Renne and others, 1993). At the same time, a new and improved definition of the Late Cretaceous and Cenozoic polarity sequence was achieved based on a comprehensive evaluation of global sea-floor magnetic anomaly profiles (Cande and Kent, 1992). This, in turn, led to a revised Cenozoic geomagnetic polarity time scale (GPTS) based on standardization to a model of South Atlantic spreading history (Cande and Kent, 1992/1995 = CK92/95). This paper presents a revised (integrated magnetobiochronologic) Cenozoic time scale (IMBTS) based on an assessment and integration of data from several sources. Biostratigraphic events are correlated to the recently revised global polarity time scale (CK95). The construction of the new GPTS is outlined with emphasis on methodology and newly developed polarity history nomenclature. The radioisotopic calibration points (as well as other relevant data) used to constrain the GPTS are reviewed in their (bio)stratigraphic context. An updated magnetobiostratigraphic (re)assessment of about 150 pre-Pliocene planktonic foraminiferal datum events (including recently avail- able high southern (austral) latitude data) and a new/modified zonal biostratigraphy provides an essentially global biostratigraphic correlation framework. This is complemented by a (re)assessment of nearly 100 calcareous nannofossil datum events. Unrecognized unconformities in the stratigraphic record (and to a lesser extent differences in taxonomic concepts), rather than latitudinal diachrony, is shown to account for discrep- ancies in magnetobiostratigraphic correlations in many instances, particularly in the Paleogene Period. Claims of diachrony of low amplitude (<2 my) are poorly substantiated, at least in the Paleocene and Eocene Epochs. Finally, we (re)assess the current status of Cenozoic chronostratigraphy and present estimates of the chronology of lower (stage) and higher (system) level units. Although the numerical values of chronostratigraphic units (and their boundaries) have changed in the decade since the previous version of the Cenozoic time scale, the relative duration of these units has remained essentially the same. This is particularly true of the Paleogene Period, where the Paleocene/Eocene and Eocene/Oligocene boundaries have been shifted ~2 my younger and the Cretaceous/Paleogene boundary ~1 my younger. Changes in the Neogene time scale are relatively minor and reflect primarily improved magnetobiostratigraphic calibrations, better understanding of chronostratigraphic and magnetobiostratigraphic relationships, and the introduction of a congruent astronom- ical/paleomagnetic chronology for the past 6 my (and concomitant adjustments to magnetochron age estimates).

@incollection{doi102110pec95040129,
    author = "Berggren, William A. and Kent, Dennis V. and Swisher, Carl C. and Aubry, Marie‐Pierre",
    title = "A Revised Cenozoic Geochronology and Chronostratigraphy",
    year = "1995",
    booktitle = "SEPM (Society for Sedimentary Geology) eBooks",
    abstract = "Since the publication of our previous time scale (Berggren and others, 1985c = BKFV85) a large amount of new magneto- and biostratigraphic data and radioisotopic ages have become available. An evaluation of some of the key magnetobiostratigraphic calibration points used in BKFV85, as suggested by high precision 40 Ar/ 39 Ar dating (e.g., Montanari and others, 1988; Swisher and Prothero, 1990; Prothero and Swisher, 1992; Prothero, 1994), has served as a catalyst for us in developing a revised Cenozoic time scale. For the Neogene Period, astrochron- ologic data (Shackleton and others, 1990; Hilgen, 1991) required re-evaluation of the calibration of the Pliocene and Pleistocene Epochs. The significantly older ages for the Pliocene-Pleistocene Epochs predicted by astronomical calibrations were soon corroborated by high precision 40 Ar/ 39 Ar dating (e.g., Baksi and others, 1992; McDougall and others, 1992; Tauxe and others, 1992; Walter and others, 1991; Renne and others, 1993). At the same time, a new and improved definition of the Late Cretaceous and Cenozoic polarity sequence was achieved based on a comprehensive evaluation of global sea-floor magnetic anomaly profiles (Cande and Kent, 1992). This, in turn, led to a revised Cenozoic geomagnetic polarity time scale (GPTS) based on standardization to a model of South Atlantic spreading history (Cande and Kent, 1992/1995 = CK92/95). This paper presents a revised (integrated magnetobiochronologic) Cenozoic time scale (IMBTS) based on an assessment and integration of data from several sources. Biostratigraphic events are correlated to the recently revised global polarity time scale (CK95). The construction of the new GPTS is outlined with emphasis on methodology and newly developed polarity history nomenclature. The radioisotopic calibration points (as well as other relevant data) used to constrain the GPTS are reviewed in their (bio)stratigraphic context. An updated magnetobiostratigraphic (re)assessment of about 150 pre-Pliocene planktonic foraminiferal datum events (including recently avail- able high southern (austral) latitude data) and a new/modified zonal biostratigraphy provides an essentially global biostratigraphic correlation framework. This is complemented by a (re)assessment of nearly 100 calcareous nannofossil datum events. Unrecognized unconformities in the stratigraphic record (and to a lesser extent differences in taxonomic concepts), rather than latitudinal diachrony, is shown to account for discrep- ancies in magnetobiostratigraphic correlations in many instances, particularly in the Paleogene Period. Claims of diachrony of low amplitude (<2 my) are poorly substantiated, at least in the Paleocene and Eocene Epochs. Finally, we (re)assess the current status of Cenozoic chronostratigraphy and present estimates of the chronology of lower (stage) and higher (system) level units. Although the numerical values of chronostratigraphic units (and their boundaries) have changed in the decade since the previous version of the Cenozoic time scale, the relative duration of these units has remained essentially the same. This is particularly true of the Paleogene Period, where the Paleocene/Eocene and Eocene/Oligocene boundaries have been shifted \textasciitilde 2 my younger and the Cretaceous/Paleogene boundary \textasciitilde 1 my younger. Changes in the Neogene time scale are relatively minor and reflect primarily improved magnetobiostratigraphic calibrations, better understanding of chronostratigraphic and magnetobiostratigraphic relationships, and the introduction of a congruent astronom- ical/paleomagnetic chronology for the past 6 my (and concomitant adjustments to magnetochron age estimates).",
    url = "https://doi.org/10.2110/pec.95.04.0129",
    doi = "10.2110/pec.95.04.0129",
    openalex = "W2130950244",
    references = "doi102110pec9504"
}

This Initial Reports volume covers Leg 162 of the cruises of the Drilling Vessel JOIDES Resolution, Edinburgh, United Kingdom, to Reykjavik, Iceland, Sites 980–987, 7 July–2 September 1995. Understanding the causes and consequences of global climatic and environmental change is an important challenge for society. The high northern latitude oceans directly influence the global environment through the formation of permanent and seasonal ice cover, transfer of sensible and latent heat to the atmosphere, and by deepwater formation and deep-ocean ventilation which control or influence both oceanic and atmospheric carbon content. Thus, any serious attempt to model and understand Cenozoic variability of global climate must take into account climate processes occurring in this region. The rationale for Leg 162 is therefore based upon the importance of the Arctic and subarctic regions to the global climate and ocean systems. This is a region where much of the world's deep waters are formed with associated large regional ocean-atmosphere heat flux. Likewise, major amplification of climate changes can occur in this region due to snow and ice albedo feedbacks. In addition, the Arctic and the Nordic Seas region may play a key active role in the long-term evolution of global climate via linkages such as the effects of gateway openings on deep circulation, altered topography due to erosion and uplift, ocean carbon fluxes, ocean alkalinity, and atmospheric CO2. Linkages between deep-ocean circulation and atmospheric CO2 have already been proposed for late Pleistocene changes at glacial-interglacial time scales. Leg 162 represents the second in a two-leg program designed to investigate three major geographic locations (the Northern Gateway region, the Greenland-Norway transect, and the Southern Gateway region), with the aim of reconstructing the temporal and spatial variability of the oceanic heat budget, the history of intermediate- and deep-water formation, and the history of glaciation on the surrounding land masses. In combination with Leg 151, the Leg 162 sites are arrayed as broad north-south and east-west transects to monitor spatial paleoclimatic variability. In addition, a vertical array of sites in the North Atlantic, Sites 980 (FENI-1), 981 (FENI-2), 982 (NAMD-1), 983 (GARDAR-1), and 984 (BJORN-1), monitors water-mass variability at the surface and at intermediate water depths. Site YERM-1 (not drilled due to ice conditions) and Site 986 (SVAL-1), deep drilling targets in the north, were planned to constrain the time of opening of the Fram Strait and water-mass exchange between the Atlantic and Arctic Oceans. The inception and history of high northern latitude glaciation are monitored on Sites 907 (ICEP-1), 985 (ICEP-3), 986 (SVAL-1), and 987 (EGM-4).

@misc{jansen1996proceedings,
    author = "Jansen, E. and Raymo, M.E. and Blum, P. and Party, The Leg 162 Science",
    title = "Proceedings of the Ocean Drilling Program Volume 162 Initial Reports: North Atlantic–Arctic Gateways II, Sites 980–987",
    year = "1996",
    publisher = "Ocean Drilling Program",
    abstract = "This Initial Reports volume covers Leg 162 of the cruises of the Drilling Vessel JOIDES Resolution, Edinburgh, United Kingdom, to Reykjavik, Iceland, Sites 980–987, 7 July–2 September 1995. Understanding the causes and consequences of global climatic and environmental change is an important challenge for society. The high northern latitude oceans directly influence the global environment through the formation of permanent and seasonal ice cover, transfer of sensible and latent heat to the atmosphere, and by deepwater formation and deep-ocean ventilation which control or influence both oceanic and atmospheric carbon content. Thus, any serious attempt to model and understand Cenozoic variability of global climate must take into account climate processes occurring in this region. The rationale for Leg 162 is therefore based upon the importance of the Arctic and subarctic regions to the global climate and ocean systems. This is a region where much of the world's deep waters are formed with associated large regional ocean-atmosphere heat flux. Likewise, major amplification of climate changes can occur in this region due to snow and ice albedo feedbacks. In addition, the Arctic and the Nordic Seas region may play a key active role in the long-term evolution of global climate via linkages such as the effects of gateway openings on deep circulation, altered topography due to erosion and uplift, ocean carbon fluxes, ocean alkalinity, and atmospheric CO2. Linkages between deep-ocean circulation and atmospheric CO2 have already been proposed for late Pleistocene changes at glacial-interglacial time scales. Leg 162 represents the second in a two-leg program designed to investigate three major geographic locations (the Northern Gateway region, the Greenland-Norway transect, and the Southern Gateway region), with the aim of reconstructing the temporal and spatial variability of the oceanic heat budget, the history of intermediate- and deep-water formation, and the history of glaciation on the surrounding land masses. In combination with Leg 151, the Leg 162 sites are arrayed as broad north-south and east-west transects to monitor spatial paleoclimatic variability. In addition, a vertical array of sites in the North Atlantic, Sites 980 (FENI-1), 981 (FENI-2), 982 (NAMD-1), 983 (GARDAR-1), and 984 (BJORN-1), monitors water-mass variability at the surface and at intermediate water depths. Site YERM-1 (not drilled due to ice conditions) and Site 986 (SVAL-1), deep drilling targets in the north, were planned to constrain the time of opening of the Fram Strait and water-mass exchange between the Atlantic and Arctic Oceans. The inception and history of high northern latitude glaciation are monitored on Sites 907 (ICEP-1), 985 (ICEP-3), 986 (SVAL-1), and 987 (EGM-4).",
    url = "https://zenodo.org/doi/10.5281/zenodo.19099781",
    doi = "10.5281/zenodo.19099781",
    openalex = "W7154243861"
}

During the last glacial period, Earth's climate underwent frequent large and abrupt global changes. This behavior appears to reflect the ability of the ocean's thermohaline circulation to assume more than one mode of operation. The record in ancient sedimentary rocks suggests that similar abrupt changes plagued the Earth at other times. The trigger mechanism for these reorganizations may have been the antiphasing of polar insolation associated with orbital cycles. Were the ongoing increase in atmospheric CO2 levels to trigger another such reorganization, it would be bad news for a world striving to feed 11 to 16 billion people.

@article{doi101126science27853431582,
    author = "Broecker, Wallace S.",
    title = "Thermohaline Circulation, the Achilles Heel of Our Climate System: Will Man-Made CO 2 Upset the Current Balance?",
    year = "1997",
    journal = "Science",
    abstract = "During the last glacial period, Earth's climate underwent frequent large and abrupt global changes. This behavior appears to reflect the ability of the ocean's thermohaline circulation to assume more than one mode of operation. The record in ancient sedimentary rocks suggests that similar abrupt changes plagued the Earth at other times. The trigger mechanism for these reorganizations may have been the antiphasing of polar insolation associated with orbital cycles. Were the ongoing increase in atmospheric CO2 levels to trigger another such reorganization, it would be bad news for a world striving to feed 11 to 16 billion people.",
    url = "https://doi.org/10.1126/science.278.5343.1582",
    doi = "10.1126/science.278.5343.1582",
    openalex = "W2091348587",
    references = "angelis1987aerosol, doi1010160031018295001719, doi101016s0146629158800144, doi101038321739a0, doi105670oceanog199107"
}

A major accomplishment of the recently completed Tropical Ocean‐Global Atmosphere (TOGA) Program was the development of an ocean observing system to support seasonal‐to‐interannual climate studies. This paper reviews the scientific motivations for the development of that observing system, the technological advances that made it possible, and the scientific advances that resulted from the availability of a significantly expanded observational database. A primary phenomenological focus of TOGA was interannual variability of the coupled ocean‐atmosphere system associated with El Niño and the Southern Oscillation (ENSO).Prior to the start of TOGA, our understanding of the physical processes responsible for the ENSO cycle was limited, our ability to monitor variability in the tropical oceans was primitive, and the capability to predict ENSO was nonexistent. TOGA therefore initiated and/or supported efforts to provide real‐time measurements of the following key oceanographic variables: surface winds, sea surface temperature, subsurface temperature, sea level and ocean velocity. Specific in situ observational programs developed to provide these data sets included the Tropical Atmosphere‐Ocean (TAO) array of moored buoys in the Pacific, a surface drifting buoy program, an island and coastal tide gauge network, and a volunteer observing ship network of expendable bathythermograph measurements. Complementing these in situ efforts were satellite missions which provided near‐global coverage of surface winds, sea surface temperature, and sea level. These new TOGA data sets led to fundamental progress in our understanding of the physical processes responsible for ENSO and to the development of coupled ocean‐atmosphere models for ENSO prediction.

@article{doi10102997jc02906,
    author = "McPhaden, Michael J. and Busalacchi, Antonio J. and Cheney, Robert E. and Donguy, Jean‐René and Gage, Kenneth S. and Halpern, David and Ji, Ming and Julian, Paul and Meyers, Gary and Mitchum, Gary T. and Niiler, Pearn P. and Picaut, Joël and Reynolds, Richard W. and Smith, Neville and Takeuchi, Kensuke",
    title = "The Tropical Ocean‐Global Atmosphere observing system: A decade of progress",
    year = "1998",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "A major accomplishment of the recently completed Tropical Ocean‐Global Atmosphere (TOGA) Program was the development of an ocean observing system to support seasonal‐to‐interannual climate studies. This paper reviews the scientific motivations for the development of that observing system, the technological advances that made it possible, and the scientific advances that resulted from the availability of a significantly expanded observational database. A primary phenomenological focus of TOGA was interannual variability of the coupled ocean‐atmosphere system associated with El Niño and the Southern Oscillation (ENSO).Prior to the start of TOGA, our understanding of the physical processes responsible for the ENSO cycle was limited, our ability to monitor variability in the tropical oceans was primitive, and the capability to predict ENSO was nonexistent. TOGA therefore initiated and/or supported efforts to provide real‐time measurements of the following key oceanographic variables: surface winds, sea surface temperature, subsurface temperature, sea level and ocean velocity. Specific in situ observational programs developed to provide these data sets included the Tropical Atmosphere‐Ocean (TAO) array of moored buoys in the Pacific, a surface drifting buoy program, an island and coastal tide gauge network, and a volunteer observing ship network of expendable bathythermograph measurements. Complementing these in situ efforts were satellite missions which provided near‐global coverage of surface winds, sea surface temperature, and sea level. These new TOGA data sets led to fundamental progress in our understanding of the physical processes responsible for ENSO and to the development of coupled ocean‐atmosphere models for ENSO prediction.",
    url = "https://doi.org/10.1029/97jc02906",
    doi = "10.1029/97jc02906",
    openalex = "W1973776704",
    references = "doi1011751520046919870442418otross20co2, doi1011751520048519830131093nmwsot20co2"
}

A unique opportunity to study rapid climate transitions in a warm climate world is provided by the Late Paleocene Thermal Maximum (LPTM), a ∼100,000 year interval during which high‐latitude temperatures suddenly rose to their highest levels in the Cenozoic. In order to explore the processes and feedbacks which may have generated or limited this brief warming event, we model the atmosphere in equilibrium with sea surface temperatures (SSTs) derived for LPTM and for conditions more representative of the late Paleocene or early Eocene. Our model results suggest that conditions during the LPTM were more equable relative to the late Paleocene or early Eocene, with the mean annual temperature range reduced by more than 5°C over much of the continental interiors and precipitation over land increased by 5–10%. Nevertheless, despite specifying warm polar SSTs which exclude sea‐ice, the model produces January continental interior temperatures less than −13°C, in contrast to proxy data estimates of higher temperatures. The zonal wind strength is drastically reduced during the LPTM, and during Northern Hemisphere winter, deep atmospheric convection over the Arctic Sea is generated owing to the specified warm SSTs. We calculate substantial wind‐driven ocean circulation response to model‐produced wind fields for these time intervals, including increases in inferred western boundary current strength of 8–28%. In general, our results are in agreement with deep‐sea sediment‐derived clay and eolian records which suggest warm, wet conditions with less vigorous atmospheric circulation during these time periods. However, major changes in the high‐latitude hydrological cycle found in our LPTM experiment results raise important questions about high‐latitude stable isotopic paleoclimate interpretations.

@article{doi1010291999jd900272,
    author = "Huber, Matthew and Sloan, L. C.",
    title = "Warm climate transitions: A general circulation modeling study of the Late Paleocene Thermal Maximum (∼56 Ma)",
    year = "1999",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "A unique opportunity to study rapid climate transitions in a warm climate world is provided by the Late Paleocene Thermal Maximum (LPTM), a ∼100,000 year interval during which high‐latitude temperatures suddenly rose to their highest levels in the Cenozoic. In order to explore the processes and feedbacks which may have generated or limited this brief warming event, we model the atmosphere in equilibrium with sea surface temperatures (SSTs) derived for LPTM and for conditions more representative of the late Paleocene or early Eocene. Our model results suggest that conditions during the LPTM were more equable relative to the late Paleocene or early Eocene, with the mean annual temperature range reduced by more than 5°C over much of the continental interiors and precipitation over land increased by 5–10\%. Nevertheless, despite specifying warm polar SSTs which exclude sea‐ice, the model produces January continental interior temperatures less than −13°C, in contrast to proxy data estimates of higher temperatures. The zonal wind strength is drastically reduced during the LPTM, and during Northern Hemisphere winter, deep atmospheric convection over the Arctic Sea is generated owing to the specified warm SSTs. We calculate substantial wind‐driven ocean circulation response to model‐produced wind fields for these time intervals, including increases in inferred western boundary current strength of 8–28\%. In general, our results are in agreement with deep‐sea sediment‐derived clay and eolian records which suggest warm, wet conditions with less vigorous atmospheric circulation during these time periods. However, major changes in the high‐latitude hydrological cycle found in our LPTM experiment results raise important questions about high‐latitude stable isotopic paleoclimate interpretations.",
    url = "https://doi.org/10.1029/1999jd900272",
    doi = "10.1029/1999jd900272",
    openalex = "W2011913903",
    references = "doi10102993pa03266, doi10102993rg03257, doi10102995pa02087, doi101029gm078p0001, doi101038353225a0, doi10106312809772, doi10111911987371, doi1011751520046919800370515nascia20co2, doi1011751520046919870442418otross20co2, doi1011751520048519830131093nmwsot20co2"
}

For the first time, a coupled general circulation model with interactive and dynamical atmospheric, oceanic, and sea‐ice components, is used to simulate an Eocene (∼50 Ma) “greenhouse” climate. We introduce efficient ocean spin‐up methods for coupled paleoclimate modeling. Sea surface temperatures (SSTs) and salinities evolve unconstrained, producing the first proxy data‐independent estimates for these Eocene climate parameters. Tropical and extratropical model‐predicted SSTs are warmer than modern values, by 3 and 5°C, respectively. Salinity‐driven deep water formation occurs in the North Atlantic and Tethys. The zonal average overturning circulation is weaker than modern. Eocene ocean heat transport is 0.6 PW less than modern in the Northern Hemisphere and 0.4 PW greater in the Southern Hemisphere. The model‐predicted near‐modern vertical and meridional Eocene temperature gradients imply that the dominant theory for maintaining low gradients—increased ocean heat transport—is incorrect or incomplete and other mechanisms should be explored.

@article{doi1010292001gl012943,
    author = "Huber, Matthew and Sloan, Lisa C.",
    title = "Heat transport, deep waters, and thermal gradients: Coupled simulation of an Eocene greenhouse climate",
    year = "2001",
    journal = "Geophysical Research Letters",
    abstract = "For the first time, a coupled general circulation model with interactive and dynamical atmospheric, oceanic, and sea‐ice components, is used to simulate an Eocene (∼50 Ma) “greenhouse” climate. We introduce efficient ocean spin‐up methods for coupled paleoclimate modeling. Sea surface temperatures (SSTs) and salinities evolve unconstrained, producing the first proxy data‐independent estimates for these Eocene climate parameters. Tropical and extratropical model‐predicted SSTs are warmer than modern values, by 3 and 5°C, respectively. Salinity‐driven deep water formation occurs in the North Atlantic and Tethys. The zonal average overturning circulation is weaker than modern. Eocene ocean heat transport is 0.6 PW less than modern in the Northern Hemisphere and 0.4 PW greater in the Southern Hemisphere. The model‐predicted near‐modern vertical and meridional Eocene temperature gradients imply that the dominant theory for maintaining low gradients—increased ocean heat transport—is incorrect or incomplete and other mechanisms should be explored.",
    url = "https://doi.org/10.1029/2001gl012943",
    doi = "10.1029/2001gl012943",
    openalex = "W1984138212",
    references = "doi1010160031018295000127, doi101017cbo9780511564512, doi1010291999jd900272, doi10102992pa01234, doi10102993pa03266, doi101029pa002i006p00741, doi101038296620a0, doi10103835021000, doi1011751520044219980111115tncsmv20co2, doi102973odpprocsr1131881990"
}

The concept of ‘Gondwana’, an ancient Southern Hemisphere supercontinent, is firmly established in geological and biogeographical models of Earth history. The term Gondwana (Gondwanaland of some authors) derives from the recognition by workers at the Indian Geological Survey in the mid- to late 19th century of a distinctive sedimentary sequence preserved in east central India. This succession, now known to range in age from Permian to Cretaceous, is lithologically and palaeontologically similar to coeval non-marine sedimentary successions developed in most of the Southern Hemisphere continents suggesting former continuity of these landmasses. Palaeomagnetic data and tectonic reconstructions suggest that the main assembly of Gondwana took place around the beginning of the Palaeozoic in near-equatorial latitudes and that the supercontinent as a whole shifted into high southern latitudes, allowing widespread glaciation by the end of the Carboniferous. From Carboniferous to Cretaceous times the southern continents had broadly similar floras but some species-level provincialism is apparent at all times. The break-up of Gondwana initiated during the Jurassic (at about 180 million years ago) and this process is continuing. The earliest rifting (crustal attenuation) within the supercontinent initiated in the west (between South America and Africa) and in general terms the rifting pattern propagated eastward with major phases of continental fragmentation in the Early Cretaceous and Late Cretaceous to Paleogene. Gondwanan floras show radical turnovers near the end of the Carboniferous, end of the Permian and the end of the Triassic that appear to be unrelated to isolation or fragmentation of the supercontinent. Throughout the late Palaeozoic and Mesozoic the high-latitude southern floras maintained a distinctly different composition to the palaeoequatorial and boreal regions even though they remained in physical connection with Laurasia for much of this time. Gondwanan floras of the Jurassic and Early Cretaceous (times immediately preceding and during break-up) were dominated by araucarian and podocarp conifers and a range of enigmatic seed-fern groups. Angiosperms became established in the region as early as the Aptian (before the final break-up events) and steadily diversified during the Cretaceous, apparently at the expense of many seed-fern groups. Hypotheses invoking vicariance or long distance dispersal to account for the biogeographic patterns evident in the floras of Southern Hemisphere continents all rely on a firm understanding of the timing and sequence of Gondwanan continental breakup. This paper aims to summarise the current understanding of the geochronological framework of Gondwanan breakup against which these biogeographic models may be tested. Most phytogeographic studies deal with the extant, angiosperm-dominated floras of these landmasses. This paper also presents an overview of pre-Cenozoic, gymnosperm-dominated, floristic provincialism in Gondwana. It documents the broad succession of pre-angiosperm floras, highlights the distinctive elements of the Early Cretaceous Gondwanan floras immediately preceding the appearance of angiosperms and suggests that latitudinal controls strongly influenced the composition of Gondwanan floras through time even in the absence of marine barriers between Gondwana and the northern continents.

@article{doi101071bt00023,
    author = "McLoughlin, Stephen",
    title = "The breakup history of Gondwana and its impact on pre-Cenozoic floristic provincialism",
    year = "2001",
    journal = "Australian Journal of Botany",
    abstract = "The concept of ‘Gondwana’, an ancient Southern Hemisphere supercontinent, is firmly established in geological and biogeographical models of Earth history. The term Gondwana (Gondwanaland of some authors) derives from the recognition by workers at the Indian Geological Survey in the mid- to late 19th century of a distinctive sedimentary sequence preserved in east central India. This succession, now known to range in age from Permian to Cretaceous, is lithologically and palaeontologically similar to coeval non-marine sedimentary successions developed in most of the Southern Hemisphere continents suggesting former continuity of these landmasses. Palaeomagnetic data and tectonic reconstructions suggest that the main assembly of Gondwana took place around the beginning of the Palaeozoic in near-equatorial latitudes and that the supercontinent as a whole shifted into high southern latitudes, allowing widespread glaciation by the end of the Carboniferous. From Carboniferous to Cretaceous times the southern continents had broadly similar floras but some species-level provincialism is apparent at all times. The break-up of Gondwana initiated during the Jurassic (at about 180 million years ago) and this process is continuing. The earliest rifting (crustal attenuation) within the supercontinent initiated in the west (between South America and Africa) and in general terms the rifting pattern propagated eastward with major phases of continental fragmentation in the Early Cretaceous and Late Cretaceous to Paleogene. Gondwanan floras show radical turnovers near the end of the Carboniferous, end of the Permian and the end of the Triassic that appear to be unrelated to isolation or fragmentation of the supercontinent. Throughout the late Palaeozoic and Mesozoic the high-latitude southern floras maintained a distinctly different composition to the palaeoequatorial and boreal regions even though they remained in physical connection with Laurasia for much of this time. Gondwanan floras of the Jurassic and Early Cretaceous (times immediately preceding and during break-up) were dominated by araucarian and podocarp conifers and a range of enigmatic seed-fern groups. Angiosperms became established in the region as early as the Aptian (before the final break-up events) and steadily diversified during the Cretaceous, apparently at the expense of many seed-fern groups. Hypotheses invoking vicariance or long distance dispersal to account for the biogeographic patterns evident in the floras of Southern Hemisphere continents all rely on a firm understanding of the timing and sequence of Gondwanan continental breakup. This paper aims to summarise the current understanding of the geochronological framework of Gondwanan breakup against which these biogeographic models may be tested. Most phytogeographic studies deal with the extant, angiosperm-dominated floras of these landmasses. This paper also presents an overview of pre-Cenozoic, gymnosperm-dominated, floristic provincialism in Gondwana. It documents the broad succession of pre-angiosperm floras, highlights the distinctive elements of the Early Cretaceous Gondwanan floras immediately preceding the appearance of angiosperms and suggests that latitudinal controls strongly influenced the composition of Gondwanan floras through time even in the absence of marine barriers between Gondwana and the northern continents.",
    url = "https://doi.org/10.1071/bt00023",
    doi = "10.1071/bt00023",
    openalex = "W1860957168",
    references = "crossref1974the, doi101007bf02860537, doi1010160012821x89900186, doi1010160031018284900373, doi1010160034666776900531, doi1010160034666782900410, doi101017s0016756800008268, doi10102993pa03266, doi101029gm032, doi101038230042a0, doi101038333547a0, doi10108003115517708527763, doi101080037362451938105591187, doi101111j150239311987tb02026x, doi10113000167606198798475lpgeig20co2, doi1011300091761319950230407scirpo23co2, doi101130spe195p1, doi101144gslmem19900120101, doi102973dsdpproc291171975, doi105962bhltitle118957, openalexw1549706842, openalexw2135985426"
}

Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10(5) to 10(7) years, rhythmic or periodic cycles driven by orbital processes with 10(4)- to 10(6)-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10(3) to 10(5) years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.

@article{doi101126science1059412,
    author = "Zachos, James C. and Pagani, Mark and Sloan, Lisa C. and Thomas, Ellen and Billups, Katharina",
    title = "Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present",
    year = "2001",
    journal = "Science",
    abstract = "Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10(5) to 10(7) years, rhythmic or periodic cycles driven by orbital processes with 10(4)- to 10(6)-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10(3) to 10(5) years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.",
    url = "https://doi.org/10.1126/science.1059412",
    doi = "10.1126/science.1059412",
    openalex = "W2115575384",
    references = "doi1010160025322771900533, doi1010160031018294902518, doi101016027737919190033q, doi10102990jb02015, doi10102993pa03266, doi10102995pa02087, doi10102996pa00571, doi10103835021000, doi101038353225a0, doi101038359117a0, doi10108004353676199311880395, doi101126science19442701121, doi101126science2875451269, doi101126science28954861897, doi1011300091761319920200569eoiseo23co2, doi1015159781400862924, doi102110pec9504, doi102110pec9554, doi102475ajs294156"
}

Revision of the GEOCARB model (Berner, 1991, 1994) for paleolevels of atmospheric CO~2~, has been made with emphasis on factors affecting CO~2~ uptake by continental weathering. This includes: (1) new GCM (general circulation model) results for the dependence of global mean surface temperature and runoff on CO~2~, for both glaciated and non-glaciated periods, coupled with new results for the temperature response to changes in solar radiation; (2) demonstration that values for the weathering-uplift factor f~R~(t) based on Sr isotopes as was done in GEOCARB II are in general agreement with independent values calculated from the abundance of terrigenous sediments as a measure of global physical erosion rate over Phanerozoic time; (3) more accurate estimates of the timing and the quantitative effects on Ca-Mg silicate weathering of the rise of large vascular plants on the continents during the Devonian; (4) inclusion of the effects of changes in paleogeography alone (constant CO~2~ and solar radiation) on global mean land surface temperature as it affects the rate of weathering; (5) consideration of the effects of volcanic weathering, both in subduction zones and on the seafloor; (6) use of new data on the δ^13^C values for Phanerozoic limestones and organic matter; (7) consideration of the relative weather- ing enhancement by gymnosperms versus angiosperms; (8) revision of paleo land area based on more recent data and use of this data, along with GCM-based paleo-runoff results, to calculate global water discharge from the continents over time. Results show a similar overall pattern to those for GEOCARB II: very high CO~2~ values during the early Paleozoic, a large drop during the Devonian and Carbonifer- ous, high values during the early Mesozoic, and a gradual decrease from about 170 Ma to low values during the Cenozoic. However, the new results exhibit considerably higher CO~2~ values during the Mesozoic, and their downward trend with time agrees with the independent estimates of Ekart and others (1999). Sensitivity analysis shows that results for paleo-CO~2~ are especially sensitive to: the effects of CO~2~ fertilization and temperature on the acceleration of plant-mediated chemical weathering; the quantitative effects of plants on mineral dissolution rate for constant temperature and CO~2~; the relative roles of angiosperms and gymnosperms in accelerating rock weather- ing; and the response of paleo-temperature to the global climate model used. This emphasizes the need for further study of the role of plants in chemical weathering and the application of GCMs to study of paleo-CO~2~ and the long term carbon cycle.

@article{doi102475ajs3012182,
    author = "Berner, Robert A.",
    title = "GEOCARB III: A revised model of atmospheric CO2 over Phanerozoic time",
    year = "2001",
    journal = "American Journal of Science",
    abstract = "Revision of the GEOCARB model (Berner, 1991, 1994) for paleolevels of atmospheric CO\textasciitilde 2\textasciitilde , has been made with emphasis on factors affecting CO\textasciitilde 2\textasciitilde\ uptake by continental weathering. This includes: (1) new GCM (general circulation model) results for the dependence of global mean surface temperature and runoff on CO\textasciitilde 2\textasciitilde , for both glaciated and non-glaciated periods, coupled with new results for the temperature response to changes in solar radiation; (2) demonstration that values for the weathering-uplift factor f\textasciitilde R\textasciitilde (t) based on Sr isotopes as was done in GEOCARB II are in general agreement with independent values calculated from the abundance of terrigenous sediments as a measure of global physical erosion rate over Phanerozoic time; (3) more accurate estimates of the timing and the quantitative effects on Ca-Mg silicate weathering of the rise of large vascular plants on the continents during the Devonian; (4) inclusion of the effects of changes in paleogeography alone (constant CO\textasciitilde 2\textasciitilde\ and solar radiation) on global mean land surface temperature as it affects the rate of weathering; (5) consideration of the effects of volcanic weathering, both in subduction zones and on the seafloor; (6) use of new data on the δ^13^C values for Phanerozoic limestones and organic matter; (7) consideration of the relative weather- ing enhancement by gymnosperms versus angiosperms; (8) revision of paleo land area based on more recent data and use of this data, along with GCM-based paleo-runoff results, to calculate global water discharge from the continents over time. Results show a similar overall pattern to those for GEOCARB II: very high CO\textasciitilde 2\textasciitilde\ values during the early Paleozoic, a large drop during the Devonian and Carbonifer- ous, high values during the early Mesozoic, and a gradual decrease from about 170 Ma to low values during the Cenozoic. However, the new results exhibit considerably higher CO\textasciitilde 2\textasciitilde\ values during the Mesozoic, and their downward trend with time agrees with the independent estimates of Ekart and others (1999). Sensitivity analysis shows that results for paleo-CO\textasciitilde 2\textasciitilde\ are especially sensitive to: the effects of CO\textasciitilde 2\textasciitilde\ fertilization and temperature on the acceleration of plant-mediated chemical weathering; the quantitative effects of plants on mineral dissolution rate for constant temperature and CO\textasciitilde 2\textasciitilde ; the relative roles of angiosperms and gymnosperms in accelerating rock weather- ing; and the response of paleo-temperature to the global climate model used. This emphasizes the need for further study of the role of plants in chemical weathering and the application of GCMs to study of paleo-CO\textasciitilde 2\textasciitilde\ and the long term carbon cycle.",
    url = "https://doi.org/10.2475/ajs.301.2.182",
    doi = "10.2475/ajs.301.2.182",
    openalex = "W4245300726",
    references = "doi1010160012821x9290070c, doi1010160012821x9600091x, doi101016001600325290625x, doi101016s0009254199000315, doi101038340457a0, doi10113000917613198210516vosstp20co2, doi10113008137233291, doi1011751520044219980111131tncfar20co2, doi102475ajs2914339, doi102475ajs294156"
}

Magnesium/calcium data from Southern Ocean planktonic foraminifera demonstrate that high-latitude (approximately 55 degrees S) southwest Pacific sea surface temperatures (SSTs) cooled 6 degrees to 7 degrees C during the middle Miocene climate transition (14.2 to 13.8 million years ago). Stepwise surface cooling is paced by eccentricity forcing and precedes Antarctic cryosphere expansion by approximately 60 thousand years, suggesting the involvement of additional feedbacks during this interval of inferred low-atmospheric partial pressure of CO2 (pCO2). Comparing SSTs and global carbon cycling proxies challenges the notion that episodic pCO2 drawdown drove this major Cenozoic climate transition. SST, salinity, and ice-volume trends suggest instead that orbitally paced ocean circulation changes altered meridional heat/vapor transport, triggering ice growth and global cooling.

@article{doi101126science1100061,
    author = "Shevenell, Amelia and Kennett, James P. and Lea, David W.",
    title = "Middle Miocene Southern Ocean Cooling and Antarctic Cryosphere Expansion",
    year = "2004",
    journal = "Science",
    abstract = "Magnesium/calcium data from Southern Ocean planktonic foraminifera demonstrate that high-latitude (approximately 55 degrees S) southwest Pacific sea surface temperatures (SSTs) cooled 6 degrees to 7 degrees C during the middle Miocene climate transition (14.2 to 13.8 million years ago). Stepwise surface cooling is paced by eccentricity forcing and precedes Antarctic cryosphere expansion by approximately 60 thousand years, suggesting the involvement of additional feedbacks during this interval of inferred low-atmospheric partial pressure of CO2 (pCO2). Comparing SSTs and global carbon cycling proxies challenges the notion that episodic pCO2 drawdown drove this major Cenozoic climate transition. SST, salinity, and ice-volume trends suggest instead that orbitally paced ocean circulation changes altered meridional heat/vapor transport, triggering ice growth and global cooling.",
    url = "https://doi.org/10.1126/science.1100061",
    doi = "10.1126/science.1100061",
    openalex = "W2070511571",
    references = "doi1010160031018294902518, doi101126science29255252310"
}

The environmental conditions of Earth, including the climate, are determined by physical, chemical, biological, and human interactions that transform and transport materials and energy. This is the "Earth system": a highly complex entity characterized by multiple nonlinear responses and thresholds, with linkages between disparate components. One important part of this system is the iron cycle, in which iron-containing soil dust is transported from land through the atmosphere to the oceans, affecting ocean biogeochemistry and hence having feedback effects on climate and dust production. Here we review the key components of this cycle, identifying critical uncertainties and priorities for future research.

@article{doi101126science1105959,
    author = "Jickells, T. D. and An, Zhisheng and Andersen, K. K. and Baker, Alex R. and Bergametti, G. and Brooks, Nick and Cao, Junji and Boyd, Philip W. and Duce, Robert A. and Hunter, Keith A. and Kawahata, Hodaka and Kubilay, N. and LaRoche, Julie and Liss, Peter S. and Mahowald, N. M. and Prospero, Joseph M. and Ridgwell, Andy and Tegen, Ina and Torres, Rodrigo",
    title = "Global Iron Connections Between Desert Dust, Ocean Biogeochemistry, and Climate",
    year = "2005",
    journal = "Science",
    abstract = {The environmental conditions of Earth, including the climate, are determined by physical, chemical, biological, and human interactions that transform and transport materials and energy. This is the "Earth system": a highly complex entity characterized by multiple nonlinear responses and thresholds, with linkages between disparate components. One important part of this system is the iron cycle, in which iron-containing soil dust is transported from land through the atmosphere to the oceans, affecting ocean biogeochemistry and hence having feedback effects on climate and dust production. Here we review the key components of this cycle, identifying critical uncertainties and priorities for future research.},
    url = "https://doi.org/10.1126/science.1105959",
    doi = "10.1126/science.1105959",
    openalex = "W2170312901",
    references = "doi10102993rg03257, doi101029pa005i001p00001, doi101126science1083545"
}

Except for a few discontinuous fragments of the Late Cretaceous/Early Cenozoic climate history and depositional environment, the paleoenvironmental evolution of the pre‐Neogene central Arctic Ocean was virtually unknown prior to the IODP Expedition 302 (Arctic Ocean Coring Expedition–ACEX) drilling campaign on Lomonosov Ridge in 2004. Here we present detailed organic carbon (OC) records from the entire ca. 200 m thick Paleogene OC‐rich section of the ACEX drill sites. These records indicate euxinic “Black Sea‐type” conditions favorable for the preservation of labile aquatic (marine algae‐type) OC occur throughout the upper part of the early Eocene and the middle Eocene, explained by salinity stratification due to freshwater discharge. The superimposed short‐term (“Milankovitch‐type”) variability in amount and composition of OC is related to changes in primary production and terrigenous input. Prominent early Eocene events of algae‐type OC preservation coincide with global δ 13 C events such as the PETM and Elmo events. The Elmo δ 13 C Event has been identified in the Arctic Ocean for the first time.

@article{doi1010292006gl026776,
    author = "Stein, Ruediger and Boucsein, Bettina and Meyer, Hanno",
    title = "Anoxia and high primary production in the Paleogene central Arctic Ocean: First detailed records from Lomonosov Ridge",
    year = "2006",
    journal = "Geophysical Research Letters",
    abstract = "Except for a few discontinuous fragments of the Late Cretaceous/Early Cenozoic climate history and depositional environment, the paleoenvironmental evolution of the pre‐Neogene central Arctic Ocean was virtually unknown prior to the IODP Expedition 302 (Arctic Ocean Coring Expedition–ACEX) drilling campaign on Lomonosov Ridge in 2004. Here we present detailed organic carbon (OC) records from the entire ca. 200 m thick Paleogene OC‐rich section of the ACEX drill sites. These records indicate euxinic “Black Sea‐type” conditions favorable for the preservation of labile aquatic (marine algae‐type) OC occur throughout the upper part of the early Eocene and the middle Eocene, explained by salinity stratification due to freshwater discharge. The superimposed short‐term (“Milankovitch‐type”) variability in amount and composition of OC is related to changes in primary production and terrigenous input. Prominent early Eocene events of algae‐type OC preservation coincide with global δ 13 C events such as the PETM and Elmo events. The Elmo δ 13 C Event has been identified in the Arctic Ocean for the first time.",
    url = "https://doi.org/10.1029/2006gl026776",
    doi = "10.1029/2006gl026776",
    openalex = "W2089951841",
    references = "doi1010079783642189128, doi1010079783642878138, doi1010160016703796002098, doi101016s0009254199000832, doi101016s0146638097000491, doi10102995pa02087, doi101029pa002i001p00001, doi101038nature04668, doi101126science1059412, openalexw2267844404"
}

The history of the Arctic Ocean during the Cenozoic era (0-65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm 'greenhouse' world, during the late Palaeocene and early Eocene epochs, to a colder 'icehouse' world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent approximately 14 Myr, we find sedimentation rates of 1-2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (approximately 3.2 Myr ago) and East Antarctic ice (approximately 14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (approximately 45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at approximately 49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (approximately 55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change.

@article{doi101038nature04800,
    author = "Moran, Kathryn and Backman, Jan and Brinkhuis, Henk and Clemens, Steven C and Cronin, Thomas and Dickens, Gerald R and Eynaud, Frédérique and Gattacceca, Jérôme and Jakobsson, Martin and Jordan, Richard W and Kaminski, Michael and King, John and Koc, Nalan and Krylov, Alexey and Martinez, Nahysa and Matthiessen, Jens and McInroy, David and Moore, Theodore C and Onodera, Jonaotaro and O'Regan, Matthew and Pälike, Heiko and Rea, Brice and Rio, Domenico and Sakamoto, Tatsuhiko and Smith, David C and Stein, Ruediger and St John, Kristen and Suto, Itsuki and Suzuki, Noritoshi and Takahashi, Kozo and Watanabe, Mahito and Yamamoto, Masanobu and Farrell, John and Frank, Martin and Kubik, Peter and Jokat, Wilfried and Kristoffersen, Yngve",
    title = "The Cenozoic palaeoenvironment of the Arctic Ocean.",
    year = "2006",
    journal = "Nature",
    abstract = "The history of the Arctic Ocean during the Cenozoic era (0-65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm 'greenhouse' world, during the late Palaeocene and early Eocene epochs, to a colder 'icehouse' world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent approximately 14 Myr, we find sedimentation rates of 1-2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (approximately 3.2 Myr ago) and East Antarctic ice (approximately 14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (approximately 45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at approximately 49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (approximately 55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change.",
    url = "https://pubmed.ncbi.nlm.nih.gov/16738653/",
    doi = "10.1038/nature04800",
    openalex = "W2123445693",
    pmid = "16738653",
    references = "doi101016003101829290096n, doi101016jquascirev200312005, doi101029jb084ib03p01071, doi101038307620a0, doi101038nature03135, doi101038nature03874, doi101038nature04668, doi101038nature05043, doi101126science27853431582, doi101126science2875451269, doi1011300813723604333, doi102110pec9504, doi102110pec9554, doi10230720033020, openalexw378346767"
}

A major element in the global climate evolution during Cenozoic times has been the transformation from warm Eocene oceans with low latitudinal and bathymetric thermal gradients into the more recent modes of circulation characterized by strong thermal gradients, oceanic fronts, cold deep oceans and cold high-latitude surface waters. In this context, however, continuous sedimentary records to be used to establish chronologic (high-resolution) sequences of climate and environmental change through Cenozoic times, were missing for the Arctic Ocean. Now, the recovery of an about 420m thick sequence of late Cretaceous/Cenozoic sediments on Lomonosov Ridge/central Arctic Ocean during the IODP-ACEX Expedition 302 in 2004 allows for the first time a detailed reconstruction of the paleoclimatic history of the early preglacial Arctic Ocean. Our study of these unique ACEX sediments will focus on the Arctic Ocean organic carbon cycle and its relationship to the longand short-term paleoenvironmental /paleoceanographic evolution during Paleocene-Eocene times. Applied methods include elemental analyses (TOC, C/N, C/S), Rock-Eval pyrolysis, biomarker studies using GC and GC/MS techniques, and stable carbon isotopes of the organic matter.

@article{s22e5e22244179531888c4e2cf0712e600ca1b1fef,
    author = "Stein, R. and Weller, P.",
    title = "The Paleocene-Eocene (Greenhouse) Arctic Ocean paleoenvironment: Implications from organic-carbon and biomarker records (IODP-ACEX Expedition 302)",
    year = "2006",
    journal = "Helmholtz-Zentrum für Polar-und Meeresforschung (Alfred-Wegener-Institut)",
    abstract = "A major element in the global climate evolution during Cenozoic times has been the transformation from warm Eocene oceans with low latitudinal and bathymetric thermal gradients into the more recent modes of circulation characterized by strong thermal gradients, oceanic fronts, cold deep oceans and cold high-latitude surface waters. In this context, however, continuous sedimentary records to be used to establish chronologic (high-resolution) sequences of climate and environmental change through Cenozoic times, were missing for the Arctic Ocean. Now, the recovery of an about 420m thick sequence of late Cretaceous/Cenozoic sediments on Lomonosov Ridge/central Arctic Ocean during the IODP-ACEX Expedition 302 in 2004 allows for the first time a detailed reconstruction of the paleoclimatic history of the early preglacial Arctic Ocean. Our study of these unique ACEX sediments will focus on the Arctic Ocean organic carbon cycle and its relationship to the longand short-term paleoenvironmental /paleoceanographic evolution during Paleocene-Eocene times. Applied methods include elemental analyses (TOC, C/N, C/S), Rock-Eval pyrolysis, biomarker studies using GC and GC/MS techniques, and stable carbon isotopes of the organic matter.",
    url = "https://www.semanticscholar.org/paper/2e5e22244179531888c4e2cf0712e600ca1b1fef",
    is_oa = "true",
    openalex = "W2278572526",
    semanticscholar_citation_count = "1",
    semanticscholar_id = "2e5e22244179531888c4e2cf0712e600ca1b1fef"
}

Abstract This study examines the double–intertropical convergence zone (ITCZ) problem in the coupled general circulation models (CGCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). The twentieth-century climate simulations of 22 IPCC AR4 CGCMs are analyzed, together with the available Atmospheric Model Intercomparison Project (AMIP) runs from 12 of them. To understand the physical mechanisms for the double-ITCZ problem, the main ocean–atmosphere feedbacks, including the zonal sea surface temperature (SST) gradient–trade wind feedback (or Bjerknes feedback), the SST–surface latent heat flux (LHF) feedback, and the SST–surface shortwave flux (SWF) feedback, are studied in detail. The results show that most of the current state-of-the-art CGCMs have some degree of the double-ITCZ problem, which is characterized by excessive precipitation over much of the Tropics (e.g., Northern Hemisphere ITCZ, South Pacific convergence zone, Maritime Continent, and equatorial Indian Ocean), and are often associated with insufficient precipitation over the equatorial Pacific. The excessive precipitation over much of the Tropics usually causes overly strong trade winds, excessive LHF, and insufficient SWF, leading to significant cold SST bias in much of the tropical oceans. Most of the models also simulate insufficient latitudinal asymmetry in precipitation and SST over the eastern Pacific and Atlantic Oceans. The AMIP runs also produce excessive precipitation over much of the Tropics, including the equatorial Pacific, which also leads to overly strong trade winds, excessive LHF, and insufficient SWF. This suggests that the excessive tropical precipitation is an intrinsic error of the atmospheric models, and that the insufficient equatorial Pacific precipitation in the coupled runs of many models comes from ocean–atmosphere feedback. Feedback analysis demonstrates that the insufficient equatorial Pacific precipitation in different models is associated with one or more of the following three biases in ocean–atmosphere feedback over the equatorial Pacific: 1) excessive Bjerknes feedback, which is caused by excessive sensitivity of precipitation to SST and overly strong time-mean surface wind speed; 2) overly positive SST–LHF feedback, which is caused by excessive sensitivity of surface air humidity to SST; and 3) insufficient SST–SWF feedback, which is caused by insufficient sensitivity of cloud amount to precipitation. Off the equator over the eastern Pacific stratus region, most of the models produce insufficient stratus–SST feedback associated with insufficient sensitivity of stratus cloud amount to SST, which may contribute to the insufficient latitudinal asymmetry of SST in their coupled runs. These results suggest that the double-ITCZ problem in CGCMs may be alleviated by reducing the excessive tropical precipitation and the above feedback-relevant errors in the atmospheric models.

@article{doi101175jcli42721,
    author = "Lin, Jialin",
    title = "The Double-ITCZ Problem in IPCC AR4 Coupled GCMs: Ocean–Atmosphere Feedback Analysis",
    year = "2007",
    journal = "Journal of Climate",
    abstract = "Abstract This study examines the double–intertropical convergence zone (ITCZ) problem in the coupled general circulation models (CGCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). The twentieth-century climate simulations of 22 IPCC AR4 CGCMs are analyzed, together with the available Atmospheric Model Intercomparison Project (AMIP) runs from 12 of them. To understand the physical mechanisms for the double-ITCZ problem, the main ocean–atmosphere feedbacks, including the zonal sea surface temperature (SST) gradient–trade wind feedback (or Bjerknes feedback), the SST–surface latent heat flux (LHF) feedback, and the SST–surface shortwave flux (SWF) feedback, are studied in detail. The results show that most of the current state-of-the-art CGCMs have some degree of the double-ITCZ problem, which is characterized by excessive precipitation over much of the Tropics (e.g., Northern Hemisphere ITCZ, South Pacific convergence zone, Maritime Continent, and equatorial Indian Ocean), and are often associated with insufficient precipitation over the equatorial Pacific. The excessive precipitation over much of the Tropics usually causes overly strong trade winds, excessive LHF, and insufficient SWF, leading to significant cold SST bias in much of the tropical oceans. Most of the models also simulate insufficient latitudinal asymmetry in precipitation and SST over the eastern Pacific and Atlantic Oceans. The AMIP runs also produce excessive precipitation over much of the Tropics, including the equatorial Pacific, which also leads to overly strong trade winds, excessive LHF, and insufficient SWF. This suggests that the excessive tropical precipitation is an intrinsic error of the atmospheric models, and that the insufficient equatorial Pacific precipitation in the coupled runs of many models comes from ocean–atmosphere feedback. Feedback analysis demonstrates that the insufficient equatorial Pacific precipitation in different models is associated with one or more of the following three biases in ocean–atmosphere feedback over the equatorial Pacific: 1) excessive Bjerknes feedback, which is caused by excessive sensitivity of precipitation to SST and overly strong time-mean surface wind speed; 2) overly positive SST–LHF feedback, which is caused by excessive sensitivity of surface air humidity to SST; and 3) insufficient SST–SWF feedback, which is caused by insufficient sensitivity of cloud amount to precipitation. Off the equator over the eastern Pacific stratus region, most of the models produce insufficient stratus–SST feedback associated with insufficient sensitivity of stratus cloud amount to SST, which may contribute to the insufficient latitudinal asymmetry of SST in their coupled runs. These results suggest that the double-ITCZ problem in CGCMs may be alleviated by reducing the excessive tropical precipitation and the above feedback-relevant errors in the atmospheric models.",
    url = "https://doi.org/10.1175/jcli4272.1",
    doi = "10.1175/jcli4272.1",
    openalex = "W2158626702",
    references = "doi1011751520046919870442418otross20co2"
}

@misc{crossref2008arctic,
    title = "Arctic Ocean",
    year = "2008",
    booktitle = "Encyclopedia of Global Warming and Climate Change",
    url = "https://doi.org/10.4135/9781412963893.n38",
    doi = "10.4135/9781412963893.n38"
}

Cenozoic biostratigraphic, cosmogenic isotope, magnetostratigraphic, and cyclostratigraphic data derived from Integrated Ocean Drilling Program Expedition 302, the Arctic Coring Expedition (ACEX), are merged into a coherent age model. This age model has low resolution because of poor core recovery, limited availability of biostratigraphic information, and the complex nature of the magnetostratigraphic record. One 2.2 Ma long hiatus occurs in the late Miocene; another spans 26 Ma (18.2–44.4 Ma). The average sedimentation rate in the recovered Cenozoic sediments is about 15 m/Ma. Core‐seismic correlation links the ACEX sediments to the reflection seismic stratigraphy of line AWI‐91090, on which the ACEX sites were drilled. This seismostratigraphy can be correlated over wide geographic areas in the central Arctic Ocean, implying that the ACEX age model can be extended well beyond the drill sites.

@article{doi1010292007pa001476,
    author = "Backman, Jan and Jakobsson, Martin and Frank, Martin and Sangiorgi, Francesca and Brinkhuis, Henk and Stickley, Catherine and O’Regan, Matt and Løvlie, Reidar and Pälike, Heiko and Spofforth, David and Gattacecca, Jérôme and Moran, Kate and King, John W. and Heil, Chip",
    title = "Age model and core‐seismic integration for the Cenozoic Arctic Coring Expedition sediments from the Lomonosov Ridge",
    year = "2008",
    journal = "Paleoceanography",
    abstract = "Cenozoic biostratigraphic, cosmogenic isotope, magnetostratigraphic, and cyclostratigraphic data derived from Integrated Ocean Drilling Program Expedition 302, the Arctic Coring Expedition (ACEX), are merged into a coherent age model. This age model has low resolution because of poor core recovery, limited availability of biostratigraphic information, and the complex nature of the magnetostratigraphic record. One 2.2 Ma long hiatus occurs in the late Miocene; another spans 26 Ma (18.2–44.4 Ma). The average sedimentation rate in the recovered Cenozoic sediments is about 15 m/Ma. Core‐seismic correlation links the ACEX sediments to the reflection seismic stratigraphy of line AWI‐91090, on which the ACEX sites were drilled. This seismostratigraphy can be correlated over wide geographic areas in the central Arctic Ocean, implying that the ACEX age model can be extended well beyond the drill sites.",
    url = "https://doi.org/10.1029/2007pa001476",
    doi = "10.1029/2007pa001476",
    openalex = "W2132360578",
    references = "doi101007978364287411613, doi101016b9780444594259000299, doi101016jquascirev200312005, doi101016s0012821x68800184, doi1010292006gl026776, doi10102994jb03098, doi101038nature04668, doi101038nature04692, doi101038nature04800, doi101038nature05043, doi1010510004636120041335, doi101126science1133822, doi1011751520046919940510210solfoa20co2, doi1011751520047719980790061apgtwa20co2"
}

We reconstruct the latest Paleocene and early Eocene (∼57–50 Ma) environmental trends in the Arctic Ocean and focus on the Paleocene‐Eocene thermal maximum (PETM) (∼55 Ma), using strata recovered from the Lomonosov Ridge by the Integrated Ocean Drilling Program Expedition 302. The Lomonosov Ridge was still partially subaerial during the latest Paleocene and earliest Eocene and gradually subsided during the early Eocene. Organic dinoflagellate cyst (dinocyst) assemblages point to brackish and productive surface waters throughout the latest Paleocene and early Eocene. Dinocyst assemblages are cosmopolitan during this time interval, suggesting warm conditions, which is corroborated by TEX 86 ′‐reconstructed temperatures of 15°–18°C. Inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower Eocene. Spectral analysis reveals that the cyclicity, recorded in X‐ray fluorescence scanning Fe data from close to Eocene thermal maximum 2 (∼53 Ma, presence confirmed by dinocyst stratigraphy), is related to precession. Within the lower part of the PETM, proxy records indicate enhanced weathering, runoff, anoxia, and productivity along with sea level rise. On the basis of total organic carbon content and variations in sediment accumulation rates, excess organic carbon burial in the Arctic Ocean appears to have contributed significantly to the sequestration of injected carbon during the PETM.

@article{doi1010292007pa001495,
    author = "Sluijs, Appy and Röhl, Ursula and Schouten, Stefan and Brumsack, Hans‐Jürgen and Sangiorgi, Francesca and Damsté, Jaap S. Sinninghe and Brinkhuis, Henk",
    title = "Arctic late Paleocene–early Eocene paleoenvironments with special emphasis on the Paleocene‐Eocene thermal maximum (Lomonosov Ridge, Integrated Ocean Drilling Program Expedition 302)",
    year = "2008",
    journal = "Paleoceanography",
    abstract = "We reconstruct the latest Paleocene and early Eocene (∼57–50 Ma) environmental trends in the Arctic Ocean and focus on the Paleocene‐Eocene thermal maximum (PETM) (∼55 Ma), using strata recovered from the Lomonosov Ridge by the Integrated Ocean Drilling Program Expedition 302. The Lomonosov Ridge was still partially subaerial during the latest Paleocene and earliest Eocene and gradually subsided during the early Eocene. Organic dinoflagellate cyst (dinocyst) assemblages point to brackish and productive surface waters throughout the latest Paleocene and early Eocene. Dinocyst assemblages are cosmopolitan during this time interval, suggesting warm conditions, which is corroborated by TEX 86 ′‐reconstructed temperatures of 15°–18°C. Inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower Eocene. Spectral analysis reveals that the cyclicity, recorded in X‐ray fluorescence scanning Fe data from close to Eocene thermal maximum 2 (∼53 Ma, presence confirmed by dinocyst stratigraphy), is related to precession. Within the lower part of the PETM, proxy records indicate enhanced weathering, runoff, anoxia, and productivity along with sea level rise. On the basis of total organic carbon content and variations in sediment accumulation rates, excess organic carbon burial in the Arctic Ocean appears to have contributed significantly to the sequestration of injected carbon during the PETM.",
    url = "https://doi.org/10.1029/2007pa001495",
    doi = "10.1029/2007pa001495",
    openalex = "W1913138165",
    references = "doi101016s0034666702002294, doi1010292006gl026776"
}

Abstract. The global climate system experienced a series of drastic changes during the Cenozoic. In Asia, these include the climate transformation from a zonal pattern to a monsoon-dominated pattern, the disappearance of typical subtropical aridity, and the onset of inland deserts. Despite major advances in the last two decades in characterizing and understanding these climate phenomena, disagreements persist relative to the timing, behaviors and underlying causes. This paper addresses these issues mainly based on two lines of evidence. First, we compiled newly collected data from geological indicators of the Cenozoic environment in China as paleoenvironmental maps of ten intervals. In confirming the earlier observation that a zonal climate pattern was transformed into a monsoonal one, the maps within the Miocene indicate that this change was achieved by the early Miocene, roughly consistent with the onset of loess deposition in China. Although a monsoon-like regime would have existed in the Eocene, it was restricted to tropical-subtropical regions. The latitudinal oscillations of the climate zones during the Paleogene are likely attributable to the imbalance in evolution of polar ice-sheets between the two hemispheres. Secondly, we examine the relevant depositional and soil forming processes of the Miocene loess-soil sequences to determine the circulation characteristics with emphasis on the early Miocene. Continuous eolian deposition in the middle reaches of the Yellow River since the early Miocene firmly indicates the formation of inland deserts, which have been constantly maintained during the past 22 Ma. Grain-size gradients between loess sections indicate northerly dust-carrying winds from northern sources, a clear indication of an Asian winter monsoon system. Meanwhile, well-developed Luvisols show evidence that moisture from the oceans reached northern China. This evidence shows the coexistence of two kinds of circulations, one from the ocean carrying moisture and another from the inland deserts transporting dust. The formation of the early Miocene paleosols resulted from interactive soil forming and dust deposition processes in these two seasonally alternating monsoonal circulations. The much stronger development of the early Miocene soils compared to those in the Quaternary loess indicates that summer monsoons were either significantly stronger, more persistent through the year, or both. These lines of evidence indicate a joint change in circulation and inland aridity by the early Miocene and suggest a dynamic linkage of them. Our recent sensitivity tests with a general circulation model, along with relevant geological data, suggest that the onset of these contrasting wet/dry responses, as well as the change from the "planetary" subtropical aridity pattern to the "inland" aridity pattern, resulted from the combined effects of Tibetan uplift and withdrawal of the Paratethys seaway in central Asia, as suggested by earlier experiments. The spreading of South China Sea also helped to enhance the south-north contrast of humidity. The Miocene loess record provides a vital insight that these tectonic factors had evolved by the early Miocene to a threshold sufficient to cause this major climate reorganization in Asia.

@article{doi105194cp41532008,
    author = "Guo, Zhengtang and Sun, Bainian and Zhang, Zhongshi and Peng, Shuyang and Xiao, Guoqiao and Ge, Junyi and Hao, Qingzhen and Qiao, Ying and Liang, Meiyan and Liu, Jianfang and Yin, Qiuzhen and Wei, J. J.",
    title = "A major reorganization of Asian climate by the early Miocene",
    year = "2008",
    journal = "Climate of the past",
    abstract = {Abstract. The global climate system experienced a series of drastic changes during the Cenozoic. In Asia, these include the climate transformation from a zonal pattern to a monsoon-dominated pattern, the disappearance of typical subtropical aridity, and the onset of inland deserts. Despite major advances in the last two decades in characterizing and understanding these climate phenomena, disagreements persist relative to the timing, behaviors and underlying causes. This paper addresses these issues mainly based on two lines of evidence. First, we compiled newly collected data from geological indicators of the Cenozoic environment in China as paleoenvironmental maps of ten intervals. In confirming the earlier observation that a zonal climate pattern was transformed into a monsoonal one, the maps within the Miocene indicate that this change was achieved by the early Miocene, roughly consistent with the onset of loess deposition in China. Although a monsoon-like regime would have existed in the Eocene, it was restricted to tropical-subtropical regions. The latitudinal oscillations of the climate zones during the Paleogene are likely attributable to the imbalance in evolution of polar ice-sheets between the two hemispheres. Secondly, we examine the relevant depositional and soil forming processes of the Miocene loess-soil sequences to determine the circulation characteristics with emphasis on the early Miocene. Continuous eolian deposition in the middle reaches of the Yellow River since the early Miocene firmly indicates the formation of inland deserts, which have been constantly maintained during the past 22 Ma. Grain-size gradients between loess sections indicate northerly dust-carrying winds from northern sources, a clear indication of an Asian winter monsoon system. Meanwhile, well-developed Luvisols show evidence that moisture from the oceans reached northern China. This evidence shows the coexistence of two kinds of circulations, one from the ocean carrying moisture and another from the inland deserts transporting dust. The formation of the early Miocene paleosols resulted from interactive soil forming and dust deposition processes in these two seasonally alternating monsoonal circulations. The much stronger development of the early Miocene soils compared to those in the Quaternary loess indicates that summer monsoons were either significantly stronger, more persistent through the year, or both. These lines of evidence indicate a joint change in circulation and inland aridity by the early Miocene and suggest a dynamic linkage of them. Our recent sensitivity tests with a general circulation model, along with relevant geological data, suggest that the onset of these contrasting wet/dry responses, as well as the change from the "planetary" subtropical aridity pattern to the "inland" aridity pattern, resulted from the combined effects of Tibetan uplift and withdrawal of the Paratethys seaway in central Asia, as suggested by earlier experiments. The spreading of South China Sea also helped to enhance the south-north contrast of humidity. The Miocene loess record provides a vital insight that these tectonic factors had evolved by the early Miocene to a threshold sufficient to cause this major climate reorganization in Asia.},
    url = "https://doi.org/10.5194/cp-4-153-2008",
    doi = "10.5194/cp-4-153-2008",
    openalex = "W2135644396",
    references = "doi10102992jb02280, doi10102994jb03098, doi101029pa002i001p00001, doi10103835021000, doi10103835075035, doi101038359117a0, doi101038416159a, doi101126science1059412, doi101126science25550521663, doi101126science2875451269"
}

Benthic foraminiferal oxygen isotopic (δ 18 O) and carbon isotopic (δ 13 C) trends, constructed from compilations of data series from multiple ocean sites, provide one of the primary means of reconstructing changes in the ocean interior. These records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records. We present new benthic foraminiferal δ 18 O and δ 13 C compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to ∼80 Ma and tentatively to ∼110 Ma. First‐order variations in interbasinal isotopic gradients delineate transitions from interior ocean heterogeneity during the Late Cretaceous (>∼65 Ma) to early Paleogene (35–65 Ma) homogeneity and a return to heterogeneity in the late Paleogene–early Neogene (35–0 Ma). We propose that these transitions reflect alterations in a first‐order characteristic of ocean circulation: the ability of winds to make water in the deep ocean circulate. We document the initiation of large interbasinal δ 18 O gradients in the early Oligocene and link the variations in interbasinal δ 18 O gradients from the middle Eocene to Oligocene with the increasing influence of wind‐driven mixing due to the gradual tectonic opening of Southern Ocean passages and initiation and strengthening of the Antarctic Circumpolar Current. The role of wind‐driven upwelling, possibly associated with a Tethyan Circumequatorial Current, in controlling Late Cretaceous interior ocean heterogeneity should be the subject of further research.

@article{doi1010292008pa001683,
    author = "Cramer, Benjamin S. and Toggweiler, J. R. and Wright, James D. and Katz, Miriam and Miller, Kenneth G.",
    title = "Ocean overturning since the Late Cretaceous: Inferences from a new benthic foraminiferal isotope compilation",
    year = "2009",
    journal = "Paleoceanography",
    abstract = "Benthic foraminiferal oxygen isotopic (δ 18 O) and carbon isotopic (δ 13 C) trends, constructed from compilations of data series from multiple ocean sites, provide one of the primary means of reconstructing changes in the ocean interior. These records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records. We present new benthic foraminiferal δ 18 O and δ 13 C compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to ∼80 Ma and tentatively to ∼110 Ma. First‐order variations in interbasinal isotopic gradients delineate transitions from interior ocean heterogeneity during the Late Cretaceous (>∼65 Ma) to early Paleogene (35–65 Ma) homogeneity and a return to heterogeneity in the late Paleogene–early Neogene (35–0 Ma). We propose that these transitions reflect alterations in a first‐order characteristic of ocean circulation: the ability of winds to make water in the deep ocean circulate. We document the initiation of large interbasinal δ 18 O gradients in the early Oligocene and link the variations in interbasinal δ 18 O gradients from the middle Eocene to Oligocene with the increasing influence of wind‐driven mixing due to the gradual tectonic opening of Southern Ocean passages and initiation and strengthening of the Antarctic Circumpolar Current. The role of wind‐driven upwelling, possibly associated with a Tethyan Circumequatorial Current, in controlling Late Cretaceous interior ocean heterogeneity should be the subject of further research.",
    url = "https://doi.org/10.1029/2008pa001683",
    doi = "10.1029/2008pa001683",
    openalex = "W1908932275",
    references = "doi1010160031018294902518, doi10102994pa01438, doi101126science2825387276, doi1011300091761319910190867ccapct23co2, doi1011300091761319920200569eoiseo23co2, doi10113008137233291, doi1011302007242401"
}

About 34 million years ago, Earth's climate shifted from a relatively ice-free world to one with glacial conditions on Antarctica characterized by substantial ice sheets. How Earth's temperature changed during this climate transition remains poorly understood, and evidence for Northern Hemisphere polar ice is controversial. Here, we report proxy records of sea surface temperatures from multiple ocean localities and show that the high-latitude temperature decrease was substantial and heterogeneous. High-latitude (45 degrees to 70 degrees in both hemispheres) temperatures before the climate transition were approximately 20 degrees C and cooled an average of approximately 5 degrees C. Our results, combined with ocean and ice-sheet model simulations and benthic oxygen isotope records, indicate that Northern Hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time.

@article{doi101126science1166368,
    author = "Liu, Zhonghui and Pagani, Mark and Zinniker, David and DeConto, Robert M. and Huber, Matthew and Brinkhuis, Henk and Walter, Sunita R. Shah and Leckie, R. Mark and Pearson, Ann",
    title = "Global Cooling During the Eocene-Oligocene Climate Transition",
    year = "2009",
    journal = "Science",
    abstract = "About 34 million years ago, Earth's climate shifted from a relatively ice-free world to one with glacial conditions on Antarctica characterized by substantial ice sheets. How Earth's temperature changed during this climate transition remains poorly understood, and evidence for Northern Hemisphere polar ice is controversial. Here, we report proxy records of sea surface temperatures from multiple ocean localities and show that the high-latitude temperature decrease was substantial and heterogeneous. High-latitude (45 degrees to 70 degrees in both hemispheres) temperatures before the climate transition were approximately 20 degrees C and cooled an average of approximately 5 degrees C. Our results, combined with ocean and ice-sheet model simulations and benthic oxygen isotope records, indicate that Northern Hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time.",
    url = "https://doi.org/10.1126/science.1166368",
    doi = "10.1126/science.1166368",
    openalex = "W2094137719",
    references = "doi101016s0031018296000995, doi10102993pa03266, doi101029jc082i027p03843, doi101038nature03135, doi101126science2875451269, doi101130spe369"
}

Abstract. Here we present a high-resolution cyclostratigraphy based on X-ray fluorescence (XRF) core scanning data from a new record retrieved from the tropical western Atlantic (Demerara Rise, ODP Leg 207, Site 1258). The Eocene sediments from ODP Site 1258 cover magnetochrons C20 to C24 and show well developed cycles. This record includes the missing interval for reevaluating the early Eocene part of the Geomagnetic Polarity Time Scale (GPTS), also providing key aspects for reconstructing high-resolution climate variability during the Early Eocene Climatic Optimum (EECO). Detailed spectral analysis demonstrates that early Eocene sedimentary cycles are characterized by precession frequencies modulated by short (100 kyr) and long (405 kyr) eccentricity with a generally minor obliquity component. Counting of both the precession and eccentricity cycles results in revised estimates for the duration of magnetochrons C21r through C24n. Our cyclostratigraphic framework also corroborates that the geochronology of the Eocene Green River Formation (Wyoming, USA) is still questionable mainly due to the uncertain correlation of the "Sixth tuff" to the GPTS. Right at the onset of the long-term Cenozoic cooling trend the dominant eccentricity-modulated precession cycles of ODP Site 1258 are interrupted by strong obliquity cycles for a period of ~800 kyr in the middle of magnetochron C22r. These distinct obliquity cycles at this low latitude site point to (1) a high-latitude driving mechanism on global climate variability from 50.1 to 49.4 Ma, and (2) seem to coincide with a significant drop in atmospheric CO2 concentration below a critical threshold between 2- and 3-times the pre-industrial level (PAL). The here newly identified orbital configuration of low eccentricity in combination with high obliquity amplitudes during this ~800-kyr period and the crossing of a critical pCO2 threshold may have led to the formation of the first ephemeral ice sheet on Antarctica as early as ~50 Ma ago.

@article{doi105194cp53092009,
    author = "Westerhold, Thomas and Röhl, Ursula",
    title = "High resolution cyclostratigraphy of the early Eocene – new insights into the origin of the Cenozoic cooling trend",
    year = "2009",
    journal = "Climate of the past",
    abstract = {Abstract. Here we present a high-resolution cyclostratigraphy based on X-ray fluorescence (XRF) core scanning data from a new record retrieved from the tropical western Atlantic (Demerara Rise, ODP Leg 207, Site 1258). The Eocene sediments from ODP Site 1258 cover magnetochrons C20 to C24 and show well developed cycles. This record includes the missing interval for reevaluating the early Eocene part of the Geomagnetic Polarity Time Scale (GPTS), also providing key aspects for reconstructing high-resolution climate variability during the Early Eocene Climatic Optimum (EECO). Detailed spectral analysis demonstrates that early Eocene sedimentary cycles are characterized by precession frequencies modulated by short (100 kyr) and long (405 kyr) eccentricity with a generally minor obliquity component. Counting of both the precession and eccentricity cycles results in revised estimates for the duration of magnetochrons C21r through C24n. Our cyclostratigraphic framework also corroborates that the geochronology of the Eocene Green River Formation (Wyoming, USA) is still questionable mainly due to the uncertain correlation of the "Sixth tuff" to the GPTS. Right at the onset of the long-term Cenozoic cooling trend the dominant eccentricity-modulated precession cycles of ODP Site 1258 are interrupted by strong obliquity cycles for a period of \textasciitilde 800 kyr in the middle of magnetochron C22r. These distinct obliquity cycles at this low latitude site point to (1) a high-latitude driving mechanism on global climate variability from 50.1 to 49.4 Ma, and (2) seem to coincide with a significant drop in atmospheric CO2 concentration below a critical threshold between 2- and 3-times the pre-industrial level (PAL). The here newly identified orbital configuration of low eccentricity in combination with high obliquity amplitudes during this \textasciitilde 800-kyr period and the crossing of a critical pCO2 threshold may have led to the formation of the first ephemeral ice sheet on Antarctica as early as \textasciitilde 50 Ma ago.},
    url = "https://doi.org/10.5194/cp-5-309-2009",
    doi = "10.5194/cp-5-309-2009",
    openalex = "W2166158246",
    references = "doi1010292006gl026776, doi1010292007pa001476"
}

[1] The carbon isotope ratio (δ13C) of plant material is commonly used to reconstruct the relative distribution of C3 and C4 plants in ancient ecosystems. However, such estimates depend on the δ13C of atmospheric CO2 (δ13CCO2) at the time, which likely varied throughout Earth history. For this study, we use benthic and planktonic δ13C and δ18O records to reconstruct a long-term record of Cenozoic δ13CCO2. Confidence intervals for δ13CCO2 values are assigned after careful consideration of equilibrium and non-equilibrium isotope effects and processes, as well as resolution of the data. We find that benthic foraminifera better constrain δ13CCO2 compared to planktonic foraminiferal records, which are influenced by photosymbiotes, depth of production, seasonal variability, and preservation. Furthermore, sensitivity analyses designed to quantify the effects of temperature uncertainty and diagenesis on benthic foraminifera δ13C and δ18O values indicate that these factors act to offset one another. Our reconstruction suggests that Cenozoic δ13CCO2 averaged −6.1 ± 0.6‰ (1σ), while only 11.2 million of the last 65.5 million years correspond to the pre-Industrial value of −6.5‰ (with 90% confidence). Here δ13CCO2 also displays significant variations throughout the record, at times departing from the pre-Industrial value by more than 2‰. Thus, the observed variability in δ13CCO2 should be considered in isotopic reconstructions of ancient terrestrial-plant ecosystems, especially during the Late and Middle Miocene, times of presumed C4 grassland expansion.

@article{doi1010292009pa001851,
    author = "Tipple, Brett J. and Meyers, Stephen R. and Pagani, Mark",
    title = "Carbon isotope ratio of Cenozoic CO 2: A comparative evaluation of available geochemical proxies",
    year = "2010",
    journal = "Paleoceanography",
    abstract = "[1] The carbon isotope ratio (δ13C) of plant material is commonly used to reconstruct the relative distribution of C3 and C4 plants in ancient ecosystems. However, such estimates depend on the δ13C of atmospheric CO2 (δ13CCO2) at the time, which likely varied throughout Earth history. For this study, we use benthic and planktonic δ13C and δ18O records to reconstruct a long-term record of Cenozoic δ13CCO2. Confidence intervals for δ13CCO2 values are assigned after careful consideration of equilibrium and non-equilibrium isotope effects and processes, as well as resolution of the data. We find that benthic foraminifera better constrain δ13CCO2 compared to planktonic foraminiferal records, which are influenced by photosymbiotes, depth of production, seasonal variability, and preservation. Furthermore, sensitivity analyses designed to quantify the effects of temperature uncertainty and diagenesis on benthic foraminifera δ13C and δ18O values indicate that these factors act to offset one another. Our reconstruction suggests that Cenozoic δ13CCO2 averaged −6.1 ± 0.6‰ (1σ), while only 11.2 million of the last 65.5 million years correspond to the pre-Industrial value of −6.5‰ (with 90\% confidence). Here δ13CCO2 also displays significant variations throughout the record, at times departing from the pre-Industrial value by more than 2‰. Thus, the observed variability in δ13CCO2 should be considered in isotopic reconstructions of ancient terrestrial-plant ecosystems, especially during the Late and Middle Miocene, times of presumed C4 grassland expansion.",
    url = "https://doi.org/10.1029/2009pa001851",
    doi = "10.1029/2009pa001851",
    openalex = "W2032903965",
    references = "doi101016jepsl200707021, doi1010292007pa001458"
}

[1] The history of the Arctic Ocean remained poorly known until the 2004 IODP coring of Lomonosov Ridge sediments. Early studies of the recovered sequence demonstrated the existence of an Eocene ‘lake-stage’ prior to the transition to marine conditions. The marine stage onset was inferred to be ∼17.5 million years -Ma- ago, thus implying a nearly 26 Ma gap between the lacustrine and marine episodes, and an unusual tectonic history for Lomonosov Ridge, in order to explain this gap. More recently, Rhenium-Osmium (Re-Os) isotope measurements of the transition from the lacustrine to marine sediments suggested a much earlier inception of marine conditions and the absence of any significant gap between both episodes. Here, an improved Osmium isotope stratigraphy and Re-Os data concur to assign a Late Eocene age (∼36 Ma) to the marine invasion, consistent with a relative change in sea level on top of Lomonosov ridge, either from tectonic origin or from another cause.

@article{doi1010292011gl047953,
    author = "Poirier, André and Hillaire‐Marcel, Claude",
    title = "Improved Os-isotope stratigraphy of the Arctic Ocean",
    year = "2011",
    journal = "Geophysical Research Letters",
    abstract = "[1] The history of the Arctic Ocean remained poorly known until the 2004 IODP coring of Lomonosov Ridge sediments. Early studies of the recovered sequence demonstrated the existence of an Eocene ‘lake-stage’ prior to the transition to marine conditions. The marine stage onset was inferred to be ∼17.5 million years -Ma- ago, thus implying a nearly 26 Ma gap between the lacustrine and marine episodes, and an unusual tectonic history for Lomonosov Ridge, in order to explain this gap. More recently, Rhenium-Osmium (Re-Os) isotope measurements of the transition from the lacustrine to marine sediments suggested a much earlier inception of marine conditions and the absence of any significant gap between both episodes. Here, an improved Osmium isotope stratigraphy and Re-Os data concur to assign a Late Eocene age (∼36 Ma) to the marine invasion, consistent with a relative change in sea level on top of Lomonosov ridge, either from tectonic origin or from another cause.",
    url = "https://doi.org/10.1029/2011gl047953",
    doi = "10.1029/2011gl047953",
    openalex = "W1591602797",
    references = "doi1010292006gl026776, doi1010292007pa001476"
}

Global cooling and the development of continental-scale Antarctic glaciation occurred in the late middle Eocene to early Oligocene (~38 to 28 million years ago), accompanied by deep-ocean reorganization attributed to gradual Antarctic Circumpolar Current (ACC) development. Our benthic foraminiferal stable isotope comparisons show that a large δ(13)C offset developed between mid-depth (~600 meters) and deep (>1000 meters) western North Atlantic waters in the early Oligocene, indicating the development of intermediate-depth δ(13)C and O(2) minima closely linked in the modern ocean to northward incursion of Antarctic Intermediate Water. At the same time, the ocean's coldest waters became restricted to south of the ACC, probably forming a bottom-ocean layer, as in the modern ocean. We show that the modern four-layer ocean structure (surface, intermediate, deep, and bottom waters) developed during the early Oligocene as a consequence of the ACC.

@article{doi101126science1202122,
    author = "Katz, Miriam and Cramer, Benjamin and Toggweiler, J. R. and Esmay, Gar and Liu, Cheng‐Jie and Miller, Kenneth G. and Rosenthal, Yair and Wade, Bridget S. and Wright, James D.",
    title = "Impact of Antarctic Circumpolar Current Development on Late Paleogene Ocean Structure",
    year = "2011",
    journal = "Science",
    abstract = "Global cooling and the development of continental-scale Antarctic glaciation occurred in the late middle Eocene to early Oligocene (\textasciitilde 38 to 28 million years ago), accompanied by deep-ocean reorganization attributed to gradual Antarctic Circumpolar Current (ACC) development. Our benthic foraminiferal stable isotope comparisons show that a large δ(13)C offset developed between mid-depth (\textasciitilde 600 meters) and deep (>1000 meters) western North Atlantic waters in the early Oligocene, indicating the development of intermediate-depth δ(13)C and O(2) minima closely linked in the modern ocean to northward incursion of Antarctic Intermediate Water. At the same time, the ocean's coldest waters became restricted to south of the ACC, probably forming a bottom-ocean layer, as in the modern ocean. We show that the modern four-layer ocean structure (surface, intermediate, deep, and bottom waters) developed during the early Oligocene as a consequence of the ACC.",
    url = "https://doi.org/10.1126/science.1202122",
    doi = "10.1126/science.1202122",
    openalex = "W1980521734",
    references = "doi10102994pa01438"
}

@misc{crossref2012arctic,
    title = "Arctic and Arctic Ocean",
    year = "2012",
    booktitle = "Encyclopedia of Global Warming \& Climate Change",
    url = "https://doi.org/10.4135/9781452218564.n35",
    doi = "10.4135/9781452218564.n35"
}

Constraining the greenhouse gas forcing, climatic warming and estimates of climate sensitivity across ancient large transient warming events is a major challenge to the palaeoclimate research community. Here we provide a new compilation and synthesis of the available marine proxy temperature data across the largest of these hyperthermals, the Paleocene–Eocene Thermal Maximum (PETM). This includes the application of consistent temperature calibrations to all data, including the most recent set of calibrations for archaeal lipid-derived palaeothermometry. This compilation provides the basis for an informed discussion of the likely range of PETM warming, the biases present in the existing record and an initial assessment of the geographical pattern of PETM ocean warming. To aid interpretation of the geographic variability of the proxy-derived estimates of PETM warming, we present a comparison of this data with the patterns of warming produced by high pCO2 simulations of Eocene climates using the Hadley Centre atmosphere-ocean general circulation model (AOGCM) HadCM3L. On the basis of this comparison and taking into account the patterns of intermediate-water warming we estimate that the global mean surface temperature anomaly for the PETM is within the range of 4 to 5 °C.

@article{doi101016jearscirev201307004,
    author = "Jones, Tom Dunkley and Lunt, Daniel J. and Schmidt, Daniela N. and Ridgwell, Andy and Sluijs, Appy and Valdes, Paul J. and Maslin, Mark",
    title = "Climate model and proxy data constraints on ocean warming across the Paleocene–Eocene Thermal Maximum",
    year = "2013",
    journal = "Earth-Science Reviews",
    abstract = "Constraining the greenhouse gas forcing, climatic warming and estimates of climate sensitivity across ancient large transient warming events is a major challenge to the palaeoclimate research community. Here we provide a new compilation and synthesis of the available marine proxy temperature data across the largest of these hyperthermals, the Paleocene–Eocene Thermal Maximum (PETM). This includes the application of consistent temperature calibrations to all data, including the most recent set of calibrations for archaeal lipid-derived palaeothermometry. This compilation provides the basis for an informed discussion of the likely range of PETM warming, the biases present in the existing record and an initial assessment of the geographical pattern of PETM ocean warming. To aid interpretation of the geographic variability of the proxy-derived estimates of PETM warming, we present a comparison of this data with the patterns of warming produced by high pCO2 simulations of Eocene climates using the Hadley Centre atmosphere-ocean general circulation model (AOGCM) HadCM3L. On the basis of this comparison and taking into account the patterns of intermediate-water warming we estimate that the global mean surface temperature anomaly for the PETM is within the range of 4 to 5 °C.",
    url = "https://doi.org/10.1016/j.earscirev.2013.07.004",
    doi = "10.1016/j.earscirev.2013.07.004",
    openalex = "W2021408515",
    references = "doi101016jepsl201206024, doi101016s0031018298000170, doi1010292011jc007255"
}

Cenozoic temperature, sea level and CO2 covariations provide insights into climate sensitivity to external forcings and sea-level sensitivity to climate change. Climate sensitivity depends on the initial climate state, but potentially can be accurately inferred from precise palaeoclimate data. Pleistocene climate oscillations yield a fast-feedback climate sensitivity of 3±1(°)C for a 4 W m(-2) CO2 forcing if Holocene warming relative to the Last Glacial Maximum (LGM) is used as calibration, but the error (uncertainty) is substantial and partly subjective because of poorly defined LGM global temperature and possible human influences in the Holocene. Glacial-to-interglacial climate change leading to the prior (Eemian) interglacial is less ambiguous and implies a sensitivity in the upper part of the above range, i.e. 3-4(°)C for a 4 W m(-2) CO2 forcing. Slow feedbacks, especially change of ice sheet size and atmospheric CO2, amplify the total Earth system sensitivity by an amount that depends on the time scale considered. Ice sheet response time is poorly defined, but we show that the slow response and hysteresis in prevailing ice sheet models are exaggerated. We use a global model, simplified to essential processes, to investigate state dependence of climate sensitivity, finding an increased sensitivity towards warmer climates, as low cloud cover is diminished and increased water vapour elevates the tropopause. Burning all fossil fuels, we conclude, would make most of the planet uninhabitable by humans, thus calling into question strategies that emphasize adaptation to climate change.

@article{doi101098rsta20120294,
    author = "Hansen, James and Sato, Makiko and Russell, Gary L. and Kharecha, Pushker",
    title = "Climate sensitivity, sea level and atmospheric carbon dioxide",
    year = "2013",
    journal = "Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences",
    abstract = "Cenozoic temperature, sea level and CO2 covariations provide insights into climate sensitivity to external forcings and sea-level sensitivity to climate change. Climate sensitivity depends on the initial climate state, but potentially can be accurately inferred from precise palaeoclimate data. Pleistocene climate oscillations yield a fast-feedback climate sensitivity of 3±1(°)C for a 4 W m(-2) CO2 forcing if Holocene warming relative to the Last Glacial Maximum (LGM) is used as calibration, but the error (uncertainty) is substantial and partly subjective because of poorly defined LGM global temperature and possible human influences in the Holocene. Glacial-to-interglacial climate change leading to the prior (Eemian) interglacial is less ambiguous and implies a sensitivity in the upper part of the above range, i.e. 3-4(°)C for a 4 W m(-2) CO2 forcing. Slow feedbacks, especially change of ice sheet size and atmospheric CO2, amplify the total Earth system sensitivity by an amount that depends on the time scale considered. Ice sheet response time is poorly defined, but we show that the slow response and hysteresis in prevailing ice sheet models are exaggerated. We use a global model, simplified to essential processes, to investigate state dependence of climate sensitivity, finding an increased sensitivity towards warmer climates, as low cloud cover is diminished and increased water vapour elevates the tropopause. Burning all fossil fuels, we conclude, would make most of the planet uninhabitable by humans, thus calling into question strategies that emphasize adaptation to climate change.",
    url = "https://doi.org/10.1098/rsta.2012.0294",
    doi = "10.1098/rsta.2012.0294",
    openalex = "W2143037254",
    references = "doi101016jepsl201206024, doi101029jc082i027p03843, doi101038nature08686, doi101126science1115159, doi1011300091761320020301067wtfftf20co2, doi105194cp76032011"
}

@incollection{crossref2014arctic,
    title = "Arctic Ocean",
    year = "2014",
    booktitle = "Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik",
    url = "https://doi.org/10.1007/978-3-642-41714-6\_12523",
    doi = "10.1007/978-3-642-41714-6\_12523",
    pages = "65-65"
}

@article{s2ae8f20919a6f1dc229afe0f3b341aae2cd2b770c,
    author = "Stein, R.",
    title = "The Great Challenges in Arctic Ocean Paleoceanography and Scientific Drilling",
    year = "2015",
    journal = "European geosciences union general assembly",
    url = "https://www.semanticscholar.org/paper/ae8f20919a6f1dc229afe0f3b341aae2cd2b770c",
    is_oa = "true",
    semanticscholar_citation_count = "2",
    semanticscholar_id = "ae8f20919a6f1dc229afe0f3b341aae2cd2b770c"
}

@incollection{crossref2016arctic,
    title = "“Arctic Ocean”",
    year = "2016",
    booktitle = "The Eastern Arctic Seas Encyclopedia",
    url = "https://doi.org/10.1007/978-3-319-24237-8\_36",
    doi = "10.1007/978-3-319-24237-8\_36",
    pages = "22-24"
}

@incollection{crossref2017arctic,
    title = "Arctic Ocean",
    year = "2017",
    booktitle = "The Western Arctic Seas Encyclopedia",
    url = "https://doi.org/10.1007/978-3-319-25582-8\_10045",
    doi = "10.1007/978-3-319-25582-8\_10045",
    pages = "21-21"
}

Abstract: Within this review paper, proxy records were used for reconstruc- tion of the late Mesozoic-Cenozoic long-term climate history of the Arctic Ocean with a focus on sea ice and sea-surface temperature. In this context, three examples representing different climatic stages of the Arctic Ocean on its way from Greenhouse to Icehouse conditions are presented and discussed: (1) the late Cretaceous, a time interval of pre-dominantly warm climate with strong seasonality and occasionally winter sea ice, some increased paleopro- ductivity, and probably oxygen-deficient conditions; (2) the mid-Eocene with continuing warm and euxinic conditions and partly increased paleoproduc- tivity, and the early onset of predominantly seasonal sea-ice conditions, and (3) the late Miocene characterized by relatively warm (SSTs of about 5 °C) and ice-free conditions during summer, as well as sea ice occurring during spring and autumn/winter.

@article{doi102312polarforschung87161,
    author = "Stein, R.",
    title = "From Greenhouse to Icehouse: The late Mesozoic-Cenozoic Arctic Ocean Sea Ice and Climate History",
    year = "2017",
    publisher = "Alfred-Wegener-Institut für Polar- und Meeresforschung und Deutsche Gesellschaft für Polarforschung",
    abstract = "Abstract: Within this review paper, proxy records were used for reconstruc- tion of the late Mesozoic-Cenozoic long-term climate history of the Arctic Ocean with a focus on sea ice and sea-surface temperature. In this context, three examples representing different climatic stages of the Arctic Ocean on its way from Greenhouse to Icehouse conditions are presented and discussed: (1) the late Cretaceous, a time interval of pre-dominantly warm climate with strong seasonality and occasionally winter sea ice, some increased paleopro- ductivity, and probably oxygen-deficient conditions; (2) the mid-Eocene with continuing warm and euxinic conditions and partly increased paleoproduc- tivity, and the early onset of predominantly seasonal sea-ice conditions, and (3) the late Miocene characterized by relatively warm (SSTs of about 5 °C) and ice-free conditions during summer, as well as sea ice occurring during spring and autumn/winter.",
    url = "https://www.semanticscholar.org/paper/80892eea0c68484ec2ace90818eb348cc132b5a0",
    doi = "10.2312/POLARFORSCHUNG.87.1.61",
    is_oa = "true",
    semanticscholar_citation_count = "1",
    semanticscholar_id = "80892eea0c68484ec2ace90818eb348cc132b5a0"
}

Abstract Earth's climate transitioned from a warm unglaciated state to a colder glaciated “icehouse” state during the Cenozoic. Extensive ice sheets were first sustained on Antarctica at the Eocene‐Oligocene Transition (EOT, ~34 Ma), but there is intense debate over whether Northern Hemisphere ice sheets developed simultaneously at this time or tens of millions of years later. Here we report on EOT‐age sediments that contain detrital sand from Integrated Ocean Drilling Program Sites U1406 and U1411 on the Newfoundland margin. These sites are ideally located to test competing hypotheses of the extent of Arctic glaciation, being situated in the North Atlantic's “iceberg alley” where icebergs, calved from both the Greenland Ice Sheet today, and the Laurentide Ice Sheet during the Pleistocene, are concentrated by the Labrador Current and deposit continentally derived detritus. Here we show that detrital sand grains present in these EOT‐aged sediments from the Newfoundland margin, initially interpreted to represent ice rafting, were sourced from the midlatitudes of North America. We find that these grains were transported to the western North Atlantic by fluvial and downslope processes, not icebergs, and were subsequently reworked and deposited by deep‐water contour currents on the Newfoundland margin. Our findings are inconsistent with the presence of extensive ice sheets on southern and western Greenland and the northeastern Canadian Arctic. This contradicts extensive bipolar glaciation at the EOT. The unipolar icehouse arose because of contrasting latitudinal continental configurations at the poles, requiring more intense Cenozoic climatic deterioration to trigger extensive Northern Hemisphere glaciation.

@article{doi1010292019pa003563,
    author = "Spray, James F. and Bohaty, Steven M. and Davies, Andrew and Bailey, Ian and Romans, Brian W. and Cooper, Matthew J. and Milton, James A. and Wilson, Paul A.",
    title = "North Atlantic Evidence for a Unipolar Icehouse Climate State at the Eocene‐Oligocene Transition",
    year = "2019",
    journal = "Paleoceanography and Paleoclimatology",
    abstract = "Abstract Earth's climate transitioned from a warm unglaciated state to a colder glaciated “icehouse” state during the Cenozoic. Extensive ice sheets were first sustained on Antarctica at the Eocene‐Oligocene Transition (EOT, \textasciitilde 34 Ma), but there is intense debate over whether Northern Hemisphere ice sheets developed simultaneously at this time or tens of millions of years later. Here we report on EOT‐age sediments that contain detrital sand from Integrated Ocean Drilling Program Sites U1406 and U1411 on the Newfoundland margin. These sites are ideally located to test competing hypotheses of the extent of Arctic glaciation, being situated in the North Atlantic's “iceberg alley” where icebergs, calved from both the Greenland Ice Sheet today, and the Laurentide Ice Sheet during the Pleistocene, are concentrated by the Labrador Current and deposit continentally derived detritus. Here we show that detrital sand grains present in these EOT‐aged sediments from the Newfoundland margin, initially interpreted to represent ice rafting, were sourced from the midlatitudes of North America. We find that these grains were transported to the western North Atlantic by fluvial and downslope processes, not icebergs, and were subsequently reworked and deposited by deep‐water contour currents on the Newfoundland margin. Our findings are inconsistent with the presence of extensive ice sheets on southern and western Greenland and the northeastern Canadian Arctic. This contradicts extensive bipolar glaciation at the EOT. The unipolar icehouse arose because of contrasting latitudinal continental configurations at the poles, requiring more intense Cenozoic climatic deterioration to trigger extensive Northern Hemisphere glaciation.",
    url = "https://doi.org/10.1029/2019pa003563",
    doi = "10.1029/2019pa003563",
    openalex = "W2948025714",
    references = "doi101016jchemgeo200406030, doi101016s0009254100001984, doi10102990jb02015, doi101029jc082i027p03843, doi101029pa004i004p00413, doi101038307620a0, doi101038nature03135, doi101126science1059412, doi101126science20043451003, doi101306d42695672b2611d78648000102c1865d"
}

The onset and evolution of the middle to late Cenozoic “icehouse” world was influenced by the development of the global ocean circulation linking the Norwegian–Greenland Sea‐Arctic Ocean to the Atlantic Ocean. The evolution of the early Neogene to early Quaternary Bjørnøyrenna Drift, located at the SW Barents Sea continental margin, shed new light on this important hydrological event. By analyzing seismic data and exploration wellbores, it is found that the drift likely started to form in the early/middle Miocene, probably as a result of an ocean circulation reorganization following the opening of the Fram Strait gateway (c. 17 Ma) and subsidence of the Greenland–Scotland Ridge (c. 12 Ma). Thus, the onset of drift growth is considered to have happened close in time to the Mid Miocene Climatic Optimum at 16–14 Ma, and was part of a regional onset of large‐scale ocean circulation in the Norwegian–Greenland Sea that influenced the subsequent climate cooling. The drift continued to grow under the influence of early Quaternary glacimarine sedimentation, and later overtopping of the drift mound by downslope transfer of glacigenic sediments during full‐glacial conditions resulted in a submarine failure. For the first time, minimum average sedimentation rates of a Neogene to Quaternary drift in this area is calculated, giving rates of 0.020–0.031 m/Kyr. These values are comparable to average deep‐sea sedimentation rates from modern low‐latitude river systems such as the Amazon and Mississippi, but lower than the Quaternary glacial sedimentation rates from the Barents Sea and Fennoscandian continental margins.

@article{doi1010292020gc009142,
    author = "Rydningen, T. A. and Høgseth, G. and Lasabuda, A. and Laberg, J. and Safronova, P. and Forwick, M.",
    title = "An Early Neogene—Early Quaternary Contourite Drift System on the SW Barents Sea Continental Margin, Norwegian Arctic",
    year = "2020",
    journal = "Geochemistry",
    abstract = "The onset and evolution of the middle to late Cenozoic “icehouse” world was influenced by the development of the global ocean circulation linking the Norwegian–Greenland Sea‐Arctic Ocean to the Atlantic Ocean. The evolution of the early Neogene to early Quaternary Bjørnøyrenna Drift, located at the SW Barents Sea continental margin, shed new light on this important hydrological event. By analyzing seismic data and exploration wellbores, it is found that the drift likely started to form in the early/middle Miocene, probably as a result of an ocean circulation reorganization following the opening of the Fram Strait gateway (c. 17 Ma) and subsidence of the Greenland–Scotland Ridge (c. 12 Ma). Thus, the onset of drift growth is considered to have happened close in time to the Mid Miocene Climatic Optimum at 16–14 Ma, and was part of a regional onset of large‐scale ocean circulation in the Norwegian–Greenland Sea that influenced the subsequent climate cooling. The drift continued to grow under the influence of early Quaternary glacimarine sedimentation, and later overtopping of the drift mound by downslope transfer of glacigenic sediments during full‐glacial conditions resulted in a submarine failure. For the first time, minimum average sedimentation rates of a Neogene to Quaternary drift in this area is calculated, giving rates of 0.020–0.031 m/Kyr. These values are comparable to average deep‐sea sedimentation rates from modern low‐latitude river systems such as the Amazon and Mississippi, but lower than the Quaternary glacial sedimentation rates from the Barents Sea and Fennoscandian continental margins.",
    url = "https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2020GC009142",
    doi = "10.1029/2020GC009142",
    is_oa = "true",
    number = "11",
    semanticscholar_citation_count = "16",
    semanticscholar_id = "cb70b649455b1064b855fdab4221588cc1651bb4",
    volume = "21"
}

Tropical Africa is home to an astonishing biodiversity occurring in a variety of ecosystems. Past climatic change and geological events have impacted the evolution and diversification of this biodiversity. During the last two decades, around 90 dated molecular phylogenies of different clades across animals and plants have been published leading to an increased understanding of the diversification and speciation processes generating tropical African biodiversity. In parallel, extended geological and palaeoclimatic records together with detailed numerical simulations have refined our understanding of past geological and climatic changes in Africa. To date, these important advances have not been reviewed within a common framework. Here, we critically review and synthesize African climate, tectonics and terrestrial biodiversity evolution throughout the Cenozoic to the mid-Pleistocene, drawing on recent advances in Earth and life sciences. We first review six major geo-climatic periods defining tropical African biodiversity diversification by synthesizing 89 dated molecular phylogeny studies. Two major geo-climatic factors impacting the diversification of the sub-Saharan biota are highlighted. First, Africa underwent numerous climatic fluctuations at ancient and more recent timescales, with tectonic, greenhouse gas, and orbital forcing stimulating diversification. Second, increased aridification since the Late Eocene led to important extinction events, but also provided unique diversification opportunities shaping the current tropical African biodiversity landscape. We then review diversification studies of tropical terrestrial animal and plant clades and discuss three major models of speciation: (i) geographic speciation via vicariance (allopatry); (ii) ecological speciation impacted by climate and geological changes, and (iii) genomic speciation via genome duplication. Geographic speciation has been the most widely documented to date and is a common speciation model across tropical Africa. We conclude with four important challenges faced by tropical African biodiversity research: (i) to increase knowledge by gathering basic and fundamental biodiversity information; (ii) to improve modelling of African geophysical evolution throughout the Cenozoic via better constraints and downscaling approaches; (iii) to increase the precision of phylogenetic reconstruction and molecular dating of tropical African clades by using next generation sequencing approaches together with better fossil calibrations; (iv) finally, as done here, to integrate data better from Earth and life sciences by focusing on the interdisciplinary study of the evolution of tropical African biodiversity in a wider geodiversity context.

@article{doi101111brv12644,
    author = "Couvreur, Thomas L. P. and Dauby, Gilles and Blach‐Overgaard, Anne and Deblauwe, Vincent and Dessein, Steven and Droissart, Vincent and Hardy, Olivier J. and Harris, David J. and Janssens, Steven B. and Ley, Alexandra C. and Mackinder, Barbara A. and Sonké, Bonaventure and Sosef, Marc S.M. and Stévart, Tariq and Svenning, Jens‐Christian and Wieringa, Jan J. and Faye, Adama and Missoup, Alain Didier and Tolley, Krystal A. and Nicolas, Violaine and Ntie, Stéphan and Fluteau, Frédéric and Robin, Cécile and Guillocheau, François and Barboni, Doris and Sepulchre, Pierre",
    title = "Tectonics, climate and the diversification of the tropical African terrestrial flora and fauna",
    year = "2020",
    journal = "Biological reviews/Biological reviews of the Cambridge Philosophical Society",
    abstract = "Tropical Africa is home to an astonishing biodiversity occurring in a variety of ecosystems. Past climatic change and geological events have impacted the evolution and diversification of this biodiversity. During the last two decades, around 90 dated molecular phylogenies of different clades across animals and plants have been published leading to an increased understanding of the diversification and speciation processes generating tropical African biodiversity. In parallel, extended geological and palaeoclimatic records together with detailed numerical simulations have refined our understanding of past geological and climatic changes in Africa. To date, these important advances have not been reviewed within a common framework. Here, we critically review and synthesize African climate, tectonics and terrestrial biodiversity evolution throughout the Cenozoic to the mid-Pleistocene, drawing on recent advances in Earth and life sciences. We first review six major geo-climatic periods defining tropical African biodiversity diversification by synthesizing 89 dated molecular phylogeny studies. Two major geo-climatic factors impacting the diversification of the sub-Saharan biota are highlighted. First, Africa underwent numerous climatic fluctuations at ancient and more recent timescales, with tectonic, greenhouse gas, and orbital forcing stimulating diversification. Second, increased aridification since the Late Eocene led to important extinction events, but also provided unique diversification opportunities shaping the current tropical African biodiversity landscape. We then review diversification studies of tropical terrestrial animal and plant clades and discuss three major models of speciation: (i) geographic speciation via vicariance (allopatry); (ii) ecological speciation impacted by climate and geological changes, and (iii) genomic speciation via genome duplication. Geographic speciation has been the most widely documented to date and is a common speciation model across tropical Africa. We conclude with four important challenges faced by tropical African biodiversity research: (i) to increase knowledge by gathering basic and fundamental biodiversity information; (ii) to improve modelling of African geophysical evolution throughout the Cenozoic via better constraints and downscaling approaches; (iii) to increase the precision of phylogenetic reconstruction and molecular dating of tropical African clades by using next generation sequencing approaches together with better fossil calibrations; (iv) finally, as done here, to integrate data better from Earth and life sciences by focusing on the interdisciplinary study of the evolution of tropical African biodiversity in a wider geodiversity context.",
    url = "https://doi.org/10.1111/brv.12644",
    doi = "10.1111/brv.12644",
    openalex = "W3086987251",
    references = "doi1010022014pa002723, doi101016jgloplacha201804004, doi101016jquascirev201406012, doi101038ngeo2813, doi101038s415610180236z, doi101038s4157601800439, doi101046j14672979200000015x, doi101093jheredesz064, doi101111j13652699201202728x, doi101111nph13230, doi101146annurevecolsys110218024737"
}

@misc{s2177a8fa1c91af4bc33c13b9f5e542ac20b0781e3,
    author = "Referee, Tom Dunkley Jones",
    title = "Interactive comment on “Late Paleocene – early Eocene Arctic Ocean Sea Surface Temperatures; reassessing biomarker paleothermometry at Lomonosov Ridge” by Appy Sluijs et al",
    year = "2020",
    url = "https://www.semanticscholar.org/paper/177a8fa1c91af4bc33c13b9f5e542ac20b0781e3",
    is_oa = "true",
    semanticscholar_id = "177a8fa1c91af4bc33c13b9f5e542ac20b0781e3"
}

Here we present a high-resolution, continuous seismostratigraphic framework that for the first time, connects the over 1,000 km long western Svalbard-Barents Sea margin and covers the last ∼2.7 million years (Ma). By exploiting recent improvements in chronology, we establish a set of reliable age fix-points from available boreholes along the margin. We then use a large 2-D seismic database to extend this consistent chronology from the Yermak Plateau and offshore western Svalbard, southwards to the Bear Island Trough-Mouth Fan. Based on this new stratigraphic framework we divide the seismic stratigraphy along the continental margin into three seismic units, and 12 regionally correlated seismic reflections, each with an estimated age assignment. We demonstrate one potential application of this framework by reconstructing the Svalbard-Barents Sea Ice Sheet evolution from the intensification of the northern hemisphere glaciation at ∼2.7 Ma to the Weichselian glaciations. Through seismic facies distribution and sedimentation rate fluctuations along the margin we distinguish three phases of glacial development. The higher temporal resolution provided by this new framework, allows us to document a clear two-step onset to glacial intensification in the region during phase 1, between ∼2.7 and 1.5 Ma. The initial step, between ∼2.7 and 2.58 Ma shows glacial expansion across Svalbard. The first indication of shelf-edge glaciation is on the Sjubrebanken Trough-Mouth Fan, northwestern Barents Sea after ∼2.58 Ma; whilst the second step, between ∼1.95 and 1.78 Ma shows glacial advances beyond Svalbard to the northwestern Barents Sea. Phase 2 is characterized by variations in sedimentation rates and the seismic facies are indicative for a regional glacial intensification for the whole Barents Sea-Svalbard region with widespread shelf-edge glaciations recorded at around ∼1.5 Ma. During Phase 3, the western Barents Sea margin is characterized by a dramatic increase in sedimentation rates, inferring once again a regional glacial intensification. Our new stratigraphic framework allows for the first time differentiation of the sediments deposited on the slope during Early Saalian (∼0.4 and 0.2 Ma), Late Saalian (∼0.2 and 0.13 Ma), and Weichselian (&lt;∼0.123 Ma) periods, providing new insights into the Barents Sea glaciations over the last ∼0.42 Ma.

@article{doi103389feart2021656732,
    author = "Alexandropoulou, Nikolitsa and Winsborrow, Monica and Andreassen, Karin and Plaza‐Faverola, Andreia and Dessandier, Pierre-Antoine and Mattingsdal, Rune and Baeten, Nicole J. and Knies, Jochen",
    title = "A Continuous Seismostratigraphic Framework for the Western Svalbard-Barents Sea Margin Over the Last 2.7 Ma: Implications for the Late Cenozoic Glacial History of the Svalbard-Barents Sea Ice Sheet",
    year = "2021",
    journal = "Frontiers in Earth Science",
    abstract = "Here we present a high-resolution, continuous seismostratigraphic framework that for the first time, connects the over 1,000 km long western Svalbard-Barents Sea margin and covers the last ∼2.7 million years (Ma). By exploiting recent improvements in chronology, we establish a set of reliable age fix-points from available boreholes along the margin. We then use a large 2-D seismic database to extend this consistent chronology from the Yermak Plateau and offshore western Svalbard, southwards to the Bear Island Trough-Mouth Fan. Based on this new stratigraphic framework we divide the seismic stratigraphy along the continental margin into three seismic units, and 12 regionally correlated seismic reflections, each with an estimated age assignment. We demonstrate one potential application of this framework by reconstructing the Svalbard-Barents Sea Ice Sheet evolution from the intensification of the northern hemisphere glaciation at ∼2.7 Ma to the Weichselian glaciations. Through seismic facies distribution and sedimentation rate fluctuations along the margin we distinguish three phases of glacial development. The higher temporal resolution provided by this new framework, allows us to document a clear two-step onset to glacial intensification in the region during phase 1, between ∼2.7 and 1.5 Ma. The initial step, between ∼2.7 and 2.58 Ma shows glacial expansion across Svalbard. The first indication of shelf-edge glaciation is on the Sjubrebanken Trough-Mouth Fan, northwestern Barents Sea after ∼2.58 Ma; whilst the second step, between ∼1.95 and 1.78 Ma shows glacial advances beyond Svalbard to the northwestern Barents Sea. Phase 2 is characterized by variations in sedimentation rates and the seismic facies are indicative for a regional glacial intensification for the whole Barents Sea-Svalbard region with widespread shelf-edge glaciations recorded at around ∼1.5 Ma. During Phase 3, the western Barents Sea margin is characterized by a dramatic increase in sedimentation rates, inferring once again a regional glacial intensification. Our new stratigraphic framework allows for the first time differentiation of the sediments deposited on the slope during Early Saalian (∼0.4 and 0.2 Ma), Late Saalian (∼0.2 and 0.13 Ma), and Weichselian (\<∼0.123 Ma) periods, providing new insights into the Barents Sea glaciations over the last ∼0.42 Ma.",
    url = "https://doi.org/10.3389/feart.2021.656732",
    doi = "10.3389/feart.2021.656732",
    openalex = "W3162467788",
    references = "doi1010292020gc009142"
}

@article{s2c3c52fc6687a2cc117cd72574a73b2a9ce9915c5,
    author = "Ruediger",
    title = "International Ocean Discovery Program Expedition 377 Scientific Prospectus",
    year = "2021",
    url = "https://www.semanticscholar.org/paper/c3c52fc6687a2cc117cd72574a73b2a9ce9915c5",
    is_oa = "true",
    semanticscholar_id = "c3c52fc6687a2cc117cd72574a73b2a9ce9915c5"
}

Today's cryosphere reflects an extreme climate state that developed through stepwise global Cenozoic cooling. In this context the opening of the Fram Strait, the Atlantic-Arctic Gateway (AAG), enabled deep-water exchange between the northern North Atlantic and the Arctic Ocean and thereby influenced global ocean circulation and climate. Here we present a new age model for Ocean Drilling Program Site 909 located in the Molloy Basin, a key site to investigate the late opening phase of the central Fram Strait and the early history of oceanic circulation in the AAG. Our results are based on a revised magnetostratigraphy calibrated by new palynomorph bioevents, which shifts previously used stratigraphies for Site 909 to significantly younger ages in the time interval from c. 15 Ma to 3 Ma. The revised late Miocene to present chronology combined with an improved core-log-seismic integration leads to a new high-resolution seismic stratigraphy for the central Fram Strait that allows a more comprehensive correlation with seismic markers from the western Barents Sea margin and also the adjacent Yermak Plateau. The new stratigraphy implies that prominent maxima in coarse sand particles and kaolinite, often interpreted as evidence for ice rafting in the Fram Strait occur at c. 10.8 Ma, c. 3 Myr later as previously inferred and thus well after the Middle Miocene Climate Transition (c. 15–13 Ma). In the late Tortonian (<7.5 Ma), sediment transport became current controlled, mainly through a western, recirculating branch of the West Spitsbergen Current. This transport was strongly enhanced between c. 6.4 and 4.6 Ma and likely linked to the subsiding Hovgaard (Hovgård) Ridge and the widening of the AAG. Late Pliocene to Pleistocene seismic reflectors correlate with episodes of elevated ice-rafted detritus input related to major steps in Northern Hemisphere ice sheet growth such as the prominent glacial inception MIS M2 that predates the mid-Piacenzian Warm Period and the intensification of Northern Hemisphere glaciation starting at c. 2.7 Ma. At the beginning of the Mid Pleistocene Transition (c. 1.2–0.8 Ma), sediment accumulation in the Fram Strait significantly decreased.

@article{doi101016jgloplacha2022103876,
    author = "Grüetzner, J. and Matthießen, Jens and Geissler, Wolfram and Gebhardt, Catalina and Schreck, Michael",
    title = "A revised core-seismic integration in the Molloy Basin (ODP Site 909): Implications for the history of ice rafting and ocean circulation in the Atlantic-Arctic gateway",
    year = "2022",
    journal = "Global and Planetary Change",
    abstract = "Today's cryosphere reflects an extreme climate state that developed through stepwise global Cenozoic cooling. In this context the opening of the Fram Strait, the Atlantic-Arctic Gateway (AAG), enabled deep-water exchange between the northern North Atlantic and the Arctic Ocean and thereby influenced global ocean circulation and climate. Here we present a new age model for Ocean Drilling Program Site 909 located in the Molloy Basin, a key site to investigate the late opening phase of the central Fram Strait and the early history of oceanic circulation in the AAG. Our results are based on a revised magnetostratigraphy calibrated by new palynomorph bioevents, which shifts previously used stratigraphies for Site 909 to significantly younger ages in the time interval from c. 15 Ma to 3 Ma. The revised late Miocene to present chronology combined with an improved core-log-seismic integration leads to a new high-resolution seismic stratigraphy for the central Fram Strait that allows a more comprehensive correlation with seismic markers from the western Barents Sea margin and also the adjacent Yermak Plateau. The new stratigraphy implies that prominent maxima in coarse sand particles and kaolinite, often interpreted as evidence for ice rafting in the Fram Strait occur at c. 10.8 Ma, c. 3 Myr later as previously inferred and thus well after the Middle Miocene Climate Transition (c. 15–13 Ma). In the late Tortonian (<7.5 Ma), sediment transport became current controlled, mainly through a western, recirculating branch of the West Spitsbergen Current. This transport was strongly enhanced between c. 6.4 and 4.6 Ma and likely linked to the subsiding Hovgaard (Hovgård) Ridge and the widening of the AAG. Late Pliocene to Pleistocene seismic reflectors correlate with episodes of elevated ice-rafted detritus input related to major steps in Northern Hemisphere ice sheet growth such as the prominent glacial inception MIS M2 that predates the mid-Piacenzian Warm Period and the intensification of Northern Hemisphere glaciation starting at c. 2.7 Ma. At the beginning of the Mid Pleistocene Transition (c. 1.2–0.8 Ma), sediment accumulation in the Fram Strait significantly decreased.",
    url = "https://doi.org/10.1016/j.gloplacha.2022.103876",
    doi = "10.1016/j.gloplacha.2022.103876",
    openalex = "W4283210535",
    references = "doi1010292020gc009142"
}

Abstract In this work, I report on the coupling of dinitrogen (N 2) fixation and denitrification in oxygen‐deficient waters of the Arctic Ocean during the Paleogene. This coupling fertilized marine phytoplankton growth and favored organic carbon burial. Reduced vertical mixing due to salinity stratification in a tectonically closed oceanic basin created conditions favorable for N 2 ‐fixation by phytoplankton harboring diazotrophic bacterial symbionts. A positive shift of 5‰ in the δ 15 N record indicates a change in the main source of biologically available nitrogen due to rapidly changing nutrient availability. I interpret this shift as a switch to Atlantic‐sourced nitrate as the main nitrogen source owing to the opening of the Arctic‐Atlantic gateway to the northern North Atlantic. While the timing of the opening is still disputed among the available Arctic records, I use evidence from the northern North Atlantic to argue that the Arctic Ocean has been fully ventilated since the early Neogene.

@article{doi1010292022gl099512,
    author = "Knies, Jochen",
    title = "Nitrogen Isotope Evidence for Changing Arctic Ocean Ventilation Regimes During the Cenozoic",
    year = "2022",
    journal = "Geophysical Research Letters",
    abstract = "Abstract In this work, I report on the coupling of dinitrogen (N 2) fixation and denitrification in oxygen‐deficient waters of the Arctic Ocean during the Paleogene. This coupling fertilized marine phytoplankton growth and favored organic carbon burial. Reduced vertical mixing due to salinity stratification in a tectonically closed oceanic basin created conditions favorable for N 2 ‐fixation by phytoplankton harboring diazotrophic bacterial symbionts. A positive shift of 5‰ in the δ 15 N record indicates a change in the main source of biologically available nitrogen due to rapidly changing nutrient availability. I interpret this shift as a switch to Atlantic‐sourced nitrate as the main nitrogen source owing to the opening of the Arctic‐Atlantic gateway to the northern North Atlantic. While the timing of the opening is still disputed among the available Arctic records, I use evidence from the northern North Atlantic to argue that the Arctic Ocean has been fully ventilated since the early Neogene.",
    url = "https://doi.org/10.1029/2022gl099512",
    doi = "10.1029/2022gl099512",
    openalex = "W4294715494",
    references = "doi1010292020gc009142"
}

Abstract At the Eocene‐Oligocene Transition (EOT), approximately 34 million years ago, Earth abruptly transitioned to a climate state sufficiently cool for Antarctica to sustain large ice sheets for the first time in tens to hundreds of millions of years. Oxygen isotope records from deep‐sea benthic foraminifera (δ 18 O b) provide the foundation of our understanding of this pivot point in Cenozoic climate history. A deeper insight, however, is hindered by the paucity of independent deep‐sea temperature reconstructions and the ongoing challenge of deconvolving the temperature and continental ice volume signals embedded in δ 18 O b records. Here we present records of deep‐sea temperature change from the eastern equatorial Pacific for the EOT using clumped isotope thermometry, which permits explicit temperature reconstructions independent of seawater chemistry and continental ice volume. Our records suggest that the deep Pacific Ocean cooled markedly at the EOT by 4.7 ± 0.9°C. This decrease in temperature represents the first direct and robust evidence of deep‐sea cooling associated with the inception of major Cenozoic glaciation. However, our data also indicate that this major cooling of the deep Pacific Ocean at the EOT was short‐lived (∼200 kyrs), with temperatures rebounding to values close to pre‐EOT levels by 33.6 Ma. Our calculated record of seawater δ 18 O suggests that this rebound in ocean temperature occurred despite the continued presence of a large‐scale Antarctic ice sheet. This finding suggests a degree of decoupling between deep ocean temperatures in the eastern equatorial Pacific Ocean and the behavior of the newly established Antarctic ice sheet.

@article{doi1010292023pa004650,
    author = "Taylor, Victoria and Wilson, Paul A. and Bohaty, Steven M. and Meckler, Anna Nele",
    title = "Transient Deep Ocean Cooling in the Eastern Equatorial Pacific Ocean at the Eocene‐Oligocene Transition",
    year = "2023",
    journal = "Paleoceanography and Paleoclimatology",
    abstract = "Abstract At the Eocene‐Oligocene Transition (EOT), approximately 34 million years ago, Earth abruptly transitioned to a climate state sufficiently cool for Antarctica to sustain large ice sheets for the first time in tens to hundreds of millions of years. Oxygen isotope records from deep‐sea benthic foraminifera (δ 18 O b) provide the foundation of our understanding of this pivot point in Cenozoic climate history. A deeper insight, however, is hindered by the paucity of independent deep‐sea temperature reconstructions and the ongoing challenge of deconvolving the temperature and continental ice volume signals embedded in δ 18 O b records. Here we present records of deep‐sea temperature change from the eastern equatorial Pacific for the EOT using clumped isotope thermometry, which permits explicit temperature reconstructions independent of seawater chemistry and continental ice volume. Our records suggest that the deep Pacific Ocean cooled markedly at the EOT by 4.7 ± 0.9°C. This decrease in temperature represents the first direct and robust evidence of deep‐sea cooling associated with the inception of major Cenozoic glaciation. However, our data also indicate that this major cooling of the deep Pacific Ocean at the EOT was short‐lived (∼200 kyrs), with temperatures rebounding to values close to pre‐EOT levels by 33.6 Ma. Our calculated record of seawater δ 18 O suggests that this rebound in ocean temperature occurred despite the continued presence of a large‐scale Antarctic ice sheet. This finding suggests a degree of decoupling between deep ocean temperatures in the eastern equatorial Pacific Ocean and the behavior of the newly established Antarctic ice sheet.",
    url = "https://doi.org/10.1029/2023pa004650",
    doi = "10.1029/2023pa004650",
    openalex = "W4385803608",
    references = "doi1010292019pa003563"
}

Abstract The late Oligocene (~27.8–23 My ago) offers an opportunity to study past climate variability under high-CO 2, warmer-than-present and the unipolar (Antarctic) glaciated state. Here, we present new high-resolution geochemical records from exquisitely well-preserved benthic foraminifera for the late Oligocene, an interval for which Antarctic ice-sheet size and stability are debated. Our records indicate four obliquity-paced glacial-interglacial cycles with ice-volume changes of up to ~70% of the modern Antarctic ice-sheet. The amplitude of ice-volume change during these late Oligocene glacial-interglacial cycles is comparable to that of the late Pliocene and early Pleistocene. Ice-volume estimates for interglacials are small enough to be accommodated by a land-based Antarctic ice-sheet but, for three of the four glacials studied, our calculations imply that ice sheets likely advanced beyond the Antarctic coastline onto the shelves. Our findings suggest an Antarctic ice-sheet vulnerable to melting driven by both bottom-up (ocean) and top-down (atmospheric) warming under late Oligocene warmer-than-present climate conditions.

@article{doi101038s43247023008649,
    author = "Brzelinski, Swaantje and Bornemann, André and Liebrand, Diederik and van Peer, Tim E. and Wilson, Paul A. and Friedrich, Oliver",
    title = "Large obliquity-paced Antarctic ice-volume fluctuations suggest melting by atmospheric and ocean warming during late Oligocene",
    year = "2023",
    journal = "Communications Earth \& Environment",
    abstract = "Abstract The late Oligocene (\textasciitilde 27.8–23 My ago) offers an opportunity to study past climate variability under high-CO 2, warmer-than-present and the unipolar (Antarctic) glaciated state. Here, we present new high-resolution geochemical records from exquisitely well-preserved benthic foraminifera for the late Oligocene, an interval for which Antarctic ice-sheet size and stability are debated. Our records indicate four obliquity-paced glacial-interglacial cycles with ice-volume changes of up to \textasciitilde 70\% of the modern Antarctic ice-sheet. The amplitude of ice-volume change during these late Oligocene glacial-interglacial cycles is comparable to that of the late Pliocene and early Pleistocene. Ice-volume estimates for interglacials are small enough to be accommodated by a land-based Antarctic ice-sheet but, for three of the four glacials studied, our calculations imply that ice sheets likely advanced beyond the Antarctic coastline onto the shelves. Our findings suggest an Antarctic ice-sheet vulnerable to melting driven by both bottom-up (ocean) and top-down (atmospheric) warming under late Oligocene warmer-than-present climate conditions.",
    url = "https://doi.org/10.1038/s43247-023-00864-9",
    doi = "10.1038/s43247-023-00864-9",
    openalex = "W4381684831",
    references = "doi1010292019pa003563"
}

Abstract Unravelling past, large-scale ocean circulation patterns is crucial for deciphering the long-term global paleoclimate. Here we apply numerical modelling to reconstruct the detailed paleobathymetry-topography of the southwestern inlet of the Barents Seaway that presently connects the Atlantic and Arctic oceans. Subaerial topography was likely enough to block Atlantic Water from entering the Barents Seaway in the earliest Eocene (c. 55 Ma). The water may have entered in the middle Eocene (c. 47 Ma) as observed from major basin subsidence, but paleotopographic highs to the east may have hindered connections between the two oceans. From the Oligocene (c. 33 Ma) until the onset of the Quaternary (c. 2.7 Ma), basin shallowing and regional shelf uplift blocked Atlantic Water from entering the Barents Seaway. Our results imply that the Fram Strait remained the sole gateway for Atlantic Water into the Arctic Ocean since its opening in the Miocene until the Quaternary.

@article{doi101038s4324702300899y,
    author = "Lasabuda, Amando and Hanssen, Alfred and Laberg, Jan Sverre and Faleide, Jan Inge and Patton, Henry and Abdelmalak, Mansour M. and Rydningen, Tom Arne and Kjølhamar, B.",
    title = "Paleobathymetric reconstructions of the SW Barents Seaway and their implications for Atlantic–Arctic ocean circulation",
    year = "2023",
    journal = "Communications Earth \& Environment",
    abstract = "Abstract Unravelling past, large-scale ocean circulation patterns is crucial for deciphering the long-term global paleoclimate. Here we apply numerical modelling to reconstruct the detailed paleobathymetry-topography of the southwestern inlet of the Barents Seaway that presently connects the Atlantic and Arctic oceans. Subaerial topography was likely enough to block Atlantic Water from entering the Barents Seaway in the earliest Eocene (c. 55 Ma). The water may have entered in the middle Eocene (c. 47 Ma) as observed from major basin subsidence, but paleotopographic highs to the east may have hindered connections between the two oceans. From the Oligocene (c. 33 Ma) until the onset of the Quaternary (c. 2.7 Ma), basin shallowing and regional shelf uplift blocked Atlantic Water from entering the Barents Seaway. Our results imply that the Fram Strait remained the sole gateway for Atlantic Water into the Arctic Ocean since its opening in the Miocene until the Quaternary.",
    url = "https://doi.org/10.1038/s43247-023-00899-y",
    doi = "10.1038/s43247-023-00899-y",
    openalex = "W4382600934",
    references = "doi1010292020gc009142"
}

Multiple ice age cycles spanning the last three million years have fundamentally transformed the Arctic landscape. The cadence and intensity of this glacial modification underpin the stability of Arctic geosystems over geologic time scales, including its hydrology, circulation patterns, slope stability, hydrocarbon fluid flow, geochemical/sediment cycling and nutrient supply. The Barents Shelf provides a unique arena to investigate long-term landscape evolution as it has undergone significant glacial modification during the Quaternary and has an extensive stratigraphic data repository motivated by decades of hydrocarbon seismic and well exploration. Here, we assimilate new geological datasets with ice sheet erosion modelling to incrementally reconstruct the geomorphic evolution of the Eurasian Arctic domain over each of the 47 glaciations since the intensification of Northern Hemisphere glaciation ∼2.74 Ma. We utilise this time-transgressive framework to review hypotheses regarding the heterogenous development of the Barents Shelf and the timing of key topographic reconfiguration episodes. Our results demonstrate that up to 2.6 km of bedrock was glacially removed to the shelf margins, and though the mean rate of erosion declines over the Quaternary, the efficacy of glacial erosion has a more complex timeline. Initially, erosion was highly effective as large expanses of the Eurasian Arctic switched from subaerial exposure to marine conditions around 2 Ma. Thereafter, erosional efficacy decreased as the landscape desensitised to successive glaciations but, after 1 Ma, it increased as a dynamic, marine-based ice sheet drained by ice streams expanded, selectively eroding large outlet troughs to the shelf edge. Critically for Arctic climate, at ∼0.69 Ma this episode of enhanced preferential erosion opened up the Barents Seaway establishing a new circulation pathway between the Atlantic and Arctic Oceans. Our 4D landscape reconstruction provides key boundary conditions for paleoclimate models and establishes a new framework for assessing the profound impact of late-Cenozoic glaciation on the Eurasian Arctic landscape.

@article{doi101016jearscirev2024104936,
    author = "Patton, Henry and Alexandropoulou, Nikolitsa and Lasabuda, Amando and Knies, Jochen and Andreassen, Karin and Winsborrow, Monica and Laberg, Jan Sverre and Hubbard, Alun",
    title = "Glacial erosion and Quaternary landscape development of the Eurasian Arctic",
    year = "2024",
    journal = "Earth-Science Reviews",
    abstract = "Multiple ice age cycles spanning the last three million years have fundamentally transformed the Arctic landscape. The cadence and intensity of this glacial modification underpin the stability of Arctic geosystems over geologic time scales, including its hydrology, circulation patterns, slope stability, hydrocarbon fluid flow, geochemical/sediment cycling and nutrient supply. The Barents Shelf provides a unique arena to investigate long-term landscape evolution as it has undergone significant glacial modification during the Quaternary and has an extensive stratigraphic data repository motivated by decades of hydrocarbon seismic and well exploration. Here, we assimilate new geological datasets with ice sheet erosion modelling to incrementally reconstruct the geomorphic evolution of the Eurasian Arctic domain over each of the 47 glaciations since the intensification of Northern Hemisphere glaciation ∼2.74 Ma. We utilise this time-transgressive framework to review hypotheses regarding the heterogenous development of the Barents Shelf and the timing of key topographic reconfiguration episodes. Our results demonstrate that up to 2.6 km of bedrock was glacially removed to the shelf margins, and though the mean rate of erosion declines over the Quaternary, the efficacy of glacial erosion has a more complex timeline. Initially, erosion was highly effective as large expanses of the Eurasian Arctic switched from subaerial exposure to marine conditions around 2 Ma. Thereafter, erosional efficacy decreased as the landscape desensitised to successive glaciations but, after 1 Ma, it increased as a dynamic, marine-based ice sheet drained by ice streams expanded, selectively eroding large outlet troughs to the shelf edge. Critically for Arctic climate, at ∼0.69 Ma this episode of enhanced preferential erosion opened up the Barents Seaway establishing a new circulation pathway between the Atlantic and Arctic Oceans. Our 4D landscape reconstruction provides key boundary conditions for paleoclimate models and establishes a new framework for assessing the profound impact of late-Cenozoic glaciation on the Eurasian Arctic landscape.",
    url = "https://doi.org/10.1016/j.earscirev.2024.104936",
    doi = "10.1016/j.earscirev.2024.104936",
    openalex = "W4402630204",
    references = "doi1010292020gc009142"
}

@incollection{crossref2025arctic,
    title = "Arctic Ocean",
    year = "2025",
    booktitle = "European State of the Climate 2024",
    url = "https://doi.org/10.18356/9789211074017c018",
    doi = "10.18356/9789211074017c018",
    pages = "72-76"
}

Abstract. Amplified Arctic warming is triggering dramatic changes to the Greenland Ice Sheet (GrIS). Studying past warm periods can provide process insights valuable to predictions of future ice sheet response. Miocene (23.03–5.33 Ma) and Pliocene (5.33–2.58 Ma) global climatic records include periods of warmer than present temperatures thought to represent analogues to near-future scenarios. Despite this, the details of the long-term glacial history of the eastern and northeastern sectors of Greenland are still largely unresolved. Here, we use seismic reflection and borehole data to describe the late Cenozoic glacial architectural development of the Northeast Greenland continental margin and thereby reconstruct long-term ice sheet evolution. We identify three key unconformable seismic surfaces that define three mega units of predominantly glacial origin. Two of the surfaces are for the first time correlated across the entire outer Northeast Greenland margin and tied to both Ocean Drilling Program Site 909 and Site 913. We show that the Late Miocene onset of shelf progradation occurs around 6.4 Ma, marking the first recorded advance of grounded ice masses across the NE Greenland shelf, forming depocentres (trough mouth fans) beyond the palaeo-shelf edge. Subsequently during the Late Miocene and Early Pliocene, the GrIS expands multiple times across the shelf, extending the continental shelf seawards. Based on the development of more extensive and thicker depocentres along the entire outer shelf and upper slope, we suggest an intensification of shelf glaciations sometime after ∼ 4.1 Ma, possibly coinciding with the intensification of the Northern Hemisphere glaciations (3.6–2.7 Ma).

@article{doi105194cp2124412025,
    author = "Jakobsen, F. W. and Winsborrow, M. and Nielsen, Tove and Laberg, J. and Plaza-Faverola, A. and Böttner, Christoph and López‐Quirós, Adrián and Planke, S. and Bellwald, B.",
    title = "Continental shelf glaciations off Northeast Greenland since the Late Miocene",
    year = "2025",
    journal = "Climate of the Past",
    abstract = "Abstract. Amplified Arctic warming is triggering dramatic changes to the Greenland Ice Sheet (GrIS). Studying past warm periods can provide process insights valuable to predictions of future ice sheet response. Miocene (23.03–5.33 Ma) and Pliocene (5.33–2.58 Ma) global climatic records include periods of warmer than present temperatures thought to represent analogues to near-future scenarios. Despite this, the details of the long-term glacial history of the eastern and northeastern sectors of Greenland are still largely unresolved. Here, we use seismic reflection and borehole data to describe the late Cenozoic glacial architectural development of the Northeast Greenland continental margin and thereby reconstruct long-term ice sheet evolution. We identify three key unconformable seismic surfaces that define three mega units of predominantly glacial origin. Two of the surfaces are for the first time correlated across the entire outer Northeast Greenland margin and tied to both Ocean Drilling Program Site 909 and Site 913. We show that the Late Miocene onset of shelf progradation occurs around 6.4 Ma, marking the first recorded advance of grounded ice masses across the NE Greenland shelf, forming depocentres (trough mouth fans) beyond the palaeo-shelf edge. Subsequently during the Late Miocene and Early Pliocene, the GrIS expands multiple times across the shelf, extending the continental shelf seawards. Based on the development of more extensive and thicker depocentres along the entire outer shelf and upper slope, we suggest an intensification of shelf glaciations sometime after ∼ 4.1 Ma, possibly coinciding with the intensification of the Northern Hemisphere glaciations (3.6–2.7 Ma).",
    url = "https://www.semanticscholar.org/paper/d0eb5cd6b5bcb9c1e6ebaee4f6d53157faab1c05",
    doi = "10.5194/cp-21-2441-2025",
    is_oa = "true",
    number = "11",
    pages = "2441-2464",
    semanticscholar_id = "d0eb5cd6b5bcb9c1e6ebaee4f6d53157faab1c05",
    volume = "21"
}

Rangifer tarandus L. plays a key role in Arctic ecosystems as the most numerous and widespread large herbivore. Sea ice is vital for maintaining genetic connectivity in Arctic islands, yet the historical role of sea ice in shaping R. tarandus biogeography is unknown. We studied the role of sea ice changes and ice sheet retreat since the last glacial period in the timing of island dispersal. We compiled published datasets of mitochondrial control region sequences that informed population history scenarios, which were evaluated in a coalescent-based approximate Bayesian computation (ABC) modelling framework to test hypotheses of island (re)colonisation and to estimate divergence and admixture. Population events were compared with modelled and proxy-based paleo-sea ice cover and published ice sheet chronologies. Our analysis supports Holocene dispersal onto deglaciated Arctic islands, rather than High Arctic glacial refugia. The degree of population admixture and the effect of sea ice were dependent on regional geography and climate history. North American initial island population divergence occurred as sea ice cover was declining. A lack of strong genetic structure and the occurrence of late Holocene admixture suggest that Canadian Arctic Archipelago populations were somewhat connected by sea ice during the Holocene. The Svalbard, Franz Josef land, and West Greenland colonisations arose through long-distance dispersal. Here, divergence times occurred post-deglaciation but broadly align with subfossil-based colonisation estimates, suggesting dispersal limitation due to sea ice conditions, potentially requiring appropriate ocean currents and sea ice drift directionality and speeds. Our study sheds light on the Late Quaternary (~60 ka-present) history of Arctic island Rangifer and suggests that ice sheet retreat, sea ice, and ocean currents were important in shaping present-day genetic patterns. Regional differences in postglacial dynamics suggest that dispersal during contemporary climate change may vary regionally and depend upon diminishing connectivity provided by sea ice.

@article{doi101002ece373125,
    author = "Dance, Maria and Saupe, Erin E and Farnsworth, Alex and Valdes, Paul J and Macias-Fauria, Marc",
    title = "Retracing the Response of Rangifer to Postglacial Climate Change in Arctic Islands.",
    year = "2026",
    journal = "Ecology and evolution",
    abstract = "Rangifer tarandus L. plays a key role in Arctic ecosystems as the most numerous and widespread large herbivore. Sea ice is vital for maintaining genetic connectivity in Arctic islands, yet the historical role of sea ice in shaping R. tarandus biogeography is unknown. We studied the role of sea ice changes and ice sheet retreat since the last glacial period in the timing of island dispersal. We compiled published datasets of mitochondrial control region sequences that informed population history scenarios, which were evaluated in a coalescent-based approximate Bayesian computation (ABC) modelling framework to test hypotheses of island (re)colonisation and to estimate divergence and admixture. Population events were compared with modelled and proxy-based paleo-sea ice cover and published ice sheet chronologies. Our analysis supports Holocene dispersal onto deglaciated Arctic islands, rather than High Arctic glacial refugia. The degree of population admixture and the effect of sea ice were dependent on regional geography and climate history. North American initial island population divergence occurred as sea ice cover was declining. A lack of strong genetic structure and the occurrence of late Holocene admixture suggest that Canadian Arctic Archipelago populations were somewhat connected by sea ice during the Holocene. The Svalbard, Franz Josef land, and West Greenland colonisations arose through long-distance dispersal. Here, divergence times occurred post-deglaciation but broadly align with subfossil-based colonisation estimates, suggesting dispersal limitation due to sea ice conditions, potentially requiring appropriate ocean currents and sea ice drift directionality and speeds. Our study sheds light on the Late Quaternary (\textasciitilde 60 ka-present) history of Arctic island Rangifer and suggests that ice sheet retreat, sea ice, and ocean currents were important in shaping present-day genetic patterns. Regional differences in postglacial dynamics suggest that dispersal during contemporary climate change may vary regionally and depend upon diminishing connectivity provided by sea ice.",
    url = "https://pmc.ncbi.nlm.nih.gov/articles/PMC13093289/",
    doi = "10.1002/ece3.73125",
    pmcid = "PMC13093289",
    pmid = "42016971"
}