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The Eocene-Oligocene Transition atc.34 million years ago (Ma) marked the global change from greenhouse to icehouse and the establishment of the East Antarctic Ice Sheet (EAIS). How the ice-sheet behaviour changed during interglacials across this climate transition is poorly understood. We analysed major, trace and rare earth elemental data of late Eocene interglacial mudstone from Prydz Bay at Ocean Drilling Program Site 1166 and early Oligocene interglacial mudstone from Integrated Ocean Drilling Program Site U1360 on the Wilkes Land continental shelf. Both sites have comparable glaciomarine depositional settings. Lithofacies and provenance at Site 1166 in Prydz Bay are indicative of a late Eocene glacial retreat in the Lambert Graben. Palaeoclimate proxies, including the Chemical Index of Alteration, mean annual temperature and mean annual precipitation, show a dominant warm and humid palaeoclimate for the late Eocene interglacial. In contrast, at Site U1360, in the early Oligocene, the provenance and interglacial weathering regime remained relatively stable with conditions of physical weathering. These results confirm that the EAIS substantially retreated periodically during late Eocene interglacials and that subglacial basins probably remained partially glaciated during interglacials in the earliest Oligocene.

 

The Eocene‐Oligocene Transition (EOT) at ∼34 Ma marked a climatic shift from greenhouse to icehouse conditions, toward long‐lasting lower global temperatures and a continental ice sheet in the Antarctic. We report on sedimentological and inorganic geochemical results across the EOT at Ocean Drilling Program (ODP) Site 696 in the Weddell Sea, within the Antarctic limb of the Atlantic circulation. The geochemical composition of detrital, authigenic and biogenic marine sediment components, and sortable silt proxies demonstrate the impact of ice growth on high latitude water masses. Sortable silt grain size and Zr/Rb ratios attest to a period of vigorous circulation at ∼36.2–35.8 Ma, coincident with a known warm interval in the Southern Ocean. Across the EOT, detrital provenance suggests that regional ice growth in the western Weddell Sea was stepwise, first expanding in the Antarctic Peninsula, followed by parts of West Antarctica. In conjunction with regional ice growth, high uranium enrichment factors (U EF) in sediments spanning the EOT interval indicate anoxic conditions in the sediment with evidence of carbonate dissolution. Following glacial expansion and sea‐ice formation at ∼33.6 Ma, a return to oxic conditions and carbonate preservation is observed with excess barium and phosphorous indicative of an increase in productivity, and potentially carbon export. Our results highlight the important connections between ice growth and the changing properties of high‐latitude water masses at the EOT with impacts on the global ocean circulation.

 

On high‐latitude continental margins sediment is supplied from land to the deep sea through a variety of processes, including iceberg and sea‐ice rafting, and bottom current transport. The accurate reconstruction of sediment fluxes from these sources through time is important in palaeoclimate reconstructions. The goal of this study was to assess a shift in the intensity of glacial processes, iceberg and sea‐ice rafting during the Pliocene through an investigation of coarse sediment deposited at the AND‐2A site in the Ross Sea and at International Ocean Discovery Program Site U1359 on the Antarctic continental rise. Terrigenous particle‐size distributions and suites of quartz grain microtextures in the sand fraction of the deep‐sea sediments were compared to those from Antarctic glaciomarine diamictites as a baseline for proximal glacial sediment in its source area. Using images acquired through Scanning Electron Microscopy, and following a quantitative approach, fewer immature and potentially glacially transported grains were found in Pliocene deep‐sea sand fractions than in ice‐contact sediments. Specifically, in the lower Pliocene interval silt and fine sand percentages are elevated, and microtextures in at least half of the sand fraction are inconsistent with a primary glacial origin. Larger numbers of chemically altered and abraded grains in the deep‐sea sand fraction, along with microtextures that are diagnostic of periglacial environments, suggest a role for eolian sediment transport. These results highlight the anomalous nature of high‐latitude sediment fluxes during prolonged periods of ice retreat. Furthermore, the identification of a significant offshore sediment flux during Antarctic deglaciation has implications for estimated nutrient supply to the Southern Ocean and the potential for high‐latitude climate feedbacks under warmer climate states.

 

The Eocene‐Oligocene transition (EOT) marks the onset of Antarctic glaciation at 33.7 Ma. Although the benthic oxygen isotope record defines the major continental ice sheet expansion, recent sedimentary and geochemical evidence suggests the presence of earlier ephemeral ice sheets. Sediment cores from Ocean Drilling Program Legs 119 and 188 in Prydz Bay provide an archive of conditions in a major drainage system of East Antarctica. We study biomarker and microfossil evidence to discern how the vegetation and climate shifted between 36 and 33 Ma. Pollen was dominated by reworked Permian Glossopterid gymnosperms; however, penecontemporaneous Eocene pollen assemblages indicate that some vegetation survived the glacial advances. At the EOT, brGDGT soil biomarkers indicate abrupt cooling from 13°C to 8°C and soil pH increases from 6.0 to 6.7, suggesting drying which is further supported by plant wax hydrogen and carbon isotopic shifts of 20‰ and 1.1‰, respectively, and evidence for drying from weathering proxies. Although the terrestrial soil biomarker influx mostly precludes the use of TEX₈₆, we find sea surface temperatures of 12°C in the late Eocene cooling to 8°C at the EOT. Marine productivity undergoes a sustained increase after the glacial advance, likely promoted by enhanced ocean circulation. Between the two glacial surge events of the Priabonian Oxygen Maximum at 37.3 Ma and the EOT at 33.7 Ma, we observe warming of 2–5°C at 35.7 and 34.7 Ma, with increase in penecontemporaneous pollen and enhanced marine productivity, capturing the last flickers of Antarctic warmth.

 

The Eocene-Oligocene Transition (EOT) at ~34 Ma marked a climatic shift from greenhouse to icehouse conditions, towards long-lasting lower global temperatures and a continental ice sheet in the Antarctic. The relative importance of ocean gateways, pCO2, and ice growth as drivers of this transition are not fully understood. We report on sedimentological and inorganic geochemical results across the EOT at Ocean Drilling Program (ODP) Site 696 in the Weddell Sea, within the Antarctic limb of the Atlantic circulation. The geochemical composition of detrital, authigenic and biogenic marine sediment components, and sortable silt proxies demonstrate the impact of ice growth on high latitude water masses. Sortable silt grain size and Zr/Rb ratios attest to a period of vigorous circulation at ~36.2-35.8 Ma, coincident with a known warm interval in the Southern Ocean. Across the EOT, detrital provenance suggests that regional ice growth in the western Weddell Sea was stepwise, first expanding in the Antarctic Peninsula, followed by parts of West Antarctica. In conjunction with regional ice growth, high uranium enrichment factors (U EF) in sediments spanning the EOT interval indicate anoxic conditions in the sediment with evidence of carbonate dissolution. Following glacial expansion and sea-ice formation at ~33.6 Ma, a return to oxic conditions and carbonate preservation is observed with excess barium and phosphorous indicative of an increase in productivity, and potentially carbon export. Our results highlight the important connections between ice growth and the changing properties of high-latitude water masses at the EOT with impacts on the global ocean circulation. 

In far-field records, the response of the East Antarctic Ice Sheet during the Pliocene shows great variability under stable greenhouse gas forcing. However, the extent, mechanisms, and feedbacks related to Pliocene Antarctic ice-sheet dynamics are poorly known from near-field archives. Here we investigate the sediment dispersal path of coarse sediment deposited as ice-rafted debris (IRD) at IODP Site U1359 on the Antarctic Wilkes Land continental rise to assess the relative importance of iceberg and sea ice rafting during the Pliocene. We analyze terrigenous particle size distributions and suites of quartz grain microtextures in ice-rafted sand in comparison to Antarctic ice-contact diamict from the Ross Sea as a baseline for glacial sediment. Using images acquired through Scanning Electron Microscopy (SEM), and following a quantitative approach, we find a smaller number of glacially weathered grains in Pliocene IRD than in ice-contact sediments, which suggests that 30-50% of the IRD is not of primary glacial or iceberg origin. Larger numbers of abraded and chemically altered grains in the IRD, along with microtextures that are diagnostic of periglacial environments, suggest a role for eolian sediment transport onto the sea ice during periods of deglaciation and then transfer to the seafloor as sea ice breaks up. Our findings are entirely consistent with modeling of the land surface exposure and surface wind field during Pliocene ice retreat. These results have implications for the interpretation of sand-dominated IRD records as proxies for ice-sheet dynamics, as well as atmospheric and oceanographic feedbacks in the high-latitude climate system.