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1. Impact of Eocene‐Oligocene Antarctic Glaciation on the Paleoceanography of the Weddell Sea

   https://doi.org/10.1029/2022PA004440  

   Hojnacki, Victoria; Lepp, Allison; Horowitz Castaldo, Josie; States, Abbey; Li, Xiaona; Passchier, Sandra (December 2022, Paleoceanography and Paleoclimatology)

   Abstract 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. 

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2. Late Eocene Record of Hydrology and Temperature From Prydz Bay, East Antarctica

   https://doi.org/10.1029/2020PA004204  

   Tibbett, Emily_J; Scher, Howie_D; Warny, Sophie; Tierney, Jessica_E; Passchier, Sandra; Feakins, Sarah_J (April 2021, Paleoceanography and Paleoclimatology)

   Abstract 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. 

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3. Early Oligocene record of an “iceberg alley” in the Weddell Sea from quartz sand microtextural analysis at ODP Site 696

   https://doi.org/10.1130/GES02686.1  

   Hojnacki, Victoria; Passchier, Sandra (May 2024, Geosphere)

   Abstract The greenhouse to icehouse transition at the Eocene-Oligocene boundary (34 Ma) marked the appearance of continental-scale glaciation in Antarctica. The material recovered from Ocean Drilling Program Site 696 is the only record spanning this major climatic shift in the Weddell Sea region. Using scanning electron microscopy, quartz microtextures in 13 samples across the Eocene-Oligocene transition were analyzed to understand the degree of glacial modification and the transportation history of the >150 µm material. The quartz grains were visually grouped, characterized, and interpreted by grain outline, relief, and surface microtextures. Glacial textures are present throughout the entire interval (34.4–33.2 Ma), with the proportion of iceberg-rafted grains in each sample decreasing into the early Oligocene (33.6 Ma), accompanied by an increase in the frequency of eolian and sea-ice-rafted grains. Mass accumulation rates reveal that the flux of iceberg-rafted debris increased coincident with the flux of eolian and sea-ice-rafted grains following 33.6 Ma, suggesting a strong coupling between land-ice development and high-latitude atmospheric processes. When compared with other Antarctic climate proxy data sets, the intensification of ice rafting at Site 696 occurred after ice-sheet inception in East Antarctica. The prominent influx of terrigenous material after 33.6 Ma points to strengthened glacial conditions accompanied by major changes in the environment of the Weddell Sea region, supporting the idea of a high-latitude role in climate perturbations, in agreement with interpretations of other global proxies. 

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4. Quartz grain microtextures illuminate Pliocene periglacial sand fluxes on the Antarctic continental margin

   https://doi.org/10.1002/dep2.157  

   Passchier, Sandra; Hansen, Melissa A.; Rosenberg, Jessica (September 2021, The Depositional Record)

   Abstract 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. 

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5. Late Holocene oceanographic and climatic variability recorded by the Perseverance Drift, northwestern Weddell Sea, based on benthic foraminifera and diatoms

   https://doi.org/10.1016/j.marmicro.2018.03.001  

   Kyrmanidou, Anastasia; Vadman, Kara J; Ishman, Scott E; Leventer, Amy; Brachfeld, Stefanie; Domack, Eugene W; Wellner, Julia S (May 2018, Marine Micropaleontology)

   The Perseverance Drift, located in the Joinville-D' Urville Trough, northwestern Weddell Sea, records changes in ocean and sea ice conditions throughout the middle to late Holocene, with a record extending back to ca. 3400 yr BP. The 2562-cm composite record collected from a water depth of 806 m, documents the uppermost section of the 90-m thick sediment drift. Spring-blooming diatoms (Chaetoceros subg. Hyalochaete) are abundant through the sedimentary record. The greater proportion of Chaetoceros vegetative valves compared to resting spores indicates that the marine environment is highly productive, and nutrients generally are not limiting. Epiphytic diatoms, dominated by Cocconeis spp., are observed throughout JKC36, suggesting transport of algal detritus from shallower regions to the benthos. Three foraminiferal assemblages (FAs): Miliammina spp., Globocassidulina spp., and Paratrochammina bartami/Paratrochammina lepida/Portatrochammina antarctica characterize the benthic foraminiferal fauna and reflect affinities with water masses circulating across the Perseverance Drift and tolerance to corrosive bottom waters. The interval 3400–1800yr BP is marked by high abundances of Globocassidulina spp., indicating incursions of Weddell Sea Transitional Water over the drift site. This interval implies a period of “freshening” of the water column, coinciding with an open-marine or seasonally open-marine environment during the middle-to-late Holocene Climatic Optimum. The interval 1800 yr BP to the present displays characteristics of slightly colder conditions, as indicated by the absence of the calcareous Globocassidulina spp. FA, and the pronounced presence of agglutinated P. bartami/P. lepida/P. antarctica FA, along with other agglutinated species that are indicative of the presence of sea ice. Therefore, this interval is interpreted to represent the onset of Neoglaciation at the northeastern tip of the Antarctic Peninsula. The consistent presence of Miliammina spp. FA corroborates that the sedimentary record represents a productive, open-marine setting with seasonally variable sea ice extent. The Drift is a unique geologic archive that provides an excellent target for future coring based on the preservation of abundant carbonate material for radiocarbon dating and the potential to develop a multi-proxy data set that could offer a robust understanding of the Holocene depositional and paleoclimatic conditions of the northwestern Weddell Sea. 

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