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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.

 

Pliocene sediments were recovered during IODP Expedition 379 within the Resolution Drift offshore the Amundsen Sea. Site U1533 was drilled on the margin of a submarine channel extending landward to the continental margin, and Site U1532 was drilled in a more distal position on the thicker portion of the drift. We present new data collected on both sites. Facies assemblages consist of greenish gray clast-bearing mud with a biosiliceous component, interbedded with dark brownish gray laminated silty clay. Due to the close proximity of Sites U1532 and U1533 and the continuous sedimentation in the early Pliocene, individual beds of each facies can be correlated between sites. The red-green channel (a*) in shipboard reflectance spectroscopy and colorimetry data for Site U1533 covaries with the facies descriptions, Ba/Rb and Br in XRF data, ICP-MS bulk elemental ratios such as Sm/Zr, and clay mineralogy. This suggests that a more greenish color of the facies is partially attributed to a larger biogenic component in the sediment relative to the terrigenous supply, and a different provenance from the gray facies. Terrigenous particle size distributions (0-2000 mu) of Site U1533 show that the gray facies are relatively uniform silty clay, whereas greenish gray units show more variability, and a sand component. Sand-rich beds are present in both facies between the top of the greenish units and the bottom of the overlying gray units, and these have a uniform fine-sand mode. Greenish gray units are tentatively interpreted as deposition during ice retreat, with reduced terrigenous supply and higher primary productivity. Although these greenish grey facies can be interpreted as interglacial units, beds with this character do not occur evenly spaced throughout the stratigraphy. Greenish grey facies coincide with low Al/Ti ratios in XRF data for Site U1533. However, Al/Ti ratios change over evenly spaced intervals with orbital frequency and likely record a more complete record of glacial-interglacial cyclicity in sediment delivery than the irregular occurrence of greenish grey facies. This would suggest that some early Pliocene interglacials did not yield suitable conditions for the deposition of the greenish gray facies, and highlights the complex interactions between the ice sheet and the ocean embedded within these paleoarchives. PLAIN LANGUAGE SUMMARY Layers of sediment extracted via deep-sea drilling from beneath the seafloor off the Amundsen Sea, Antarctica, were stacked up over millions of years. The layers were built by pulses of sediment supplied from land ice and biogenic blooms, with distribution of material by ocean currents. The changing color and composition of the layers is an indication of the dominant imprint of ice-related processes versus ocean processes on the sediments that were raining down on the seafloor at any given time. Sedimentation related to the ice and the ocean follows different rhythms related to distribution of heat over time at different latitudes on Earth. The climate archive studied here records how the interference of these rhythms produces ice ages in Antarctica in a previous warm period about 3 to 5 million years ago with atmospheric greenhouse conditions that were like those of today. Investigations of these polar geological climate archives help provide context for the current ice mass loss observed in this same area of Antarctica and its potential sea-level effects. 

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. 

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) 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.

 

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.