More Like this

1. Eolian sand dispersal via sea ice on the Antarctic continental margin during Pliocene deglaciation

   Sandra Passchier, Melissa Hansen (December 2020, American Geophysical Union)

   null (Ed.)

   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. 

   more » « less
2. 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. 

   more » « less
3. Direct link between iceberg melt and diatom productivity demonstrated in Mid-Pliocene Amundsen Sea interglacial sediments

   https://doi.org/10.5194/jm-43-269-2024  

   Furlong, Heather; Scherer, Reed Paul (January 2024, Journal of Micropalaeontology)

   Sangiorgi, Francesca (Ed.)

   Abstract. Iceberg influence on diatom productivity has been observed for the present and suggested for the past, but direct seeding of the Southern Ocean during times of ice sheet collapse has never been directly demonstrated. Here we demonstrate enhanced diatom production and accumulation in the Amundsen Sea during a Mid-Pliocene interglacial that precisely coincides with pulses of ice-rafted debris (IRD) accumulation, and we infer a causal relation. International Ocean Discovery Program (IODP) Expedition 379 obtained continuous sediment records from the Amundsen Sea continental rise to document West Antarctic Ice Sheet (WAIS) history in an area currently experiencing the largest ice loss in Antarctica. Scanning electron microscopy (SEM) imagery of Mid-Pliocene interglacial sediments of Marine Isotope Stage (MIS) (GI-17, ∼ 3.9 Ma) documents distinct intervals of IRD-rich diatomite, whereas the overall diatom abundance and concentration of bloom species is relatively low in the absence of visible IRD. Sand- and granule-sized IRD grains are documented fully encased within diatomite laminae, with some displaying soft-sediment micro-deformation formed by grains falling into soft diatom ooze. IRD-rich diatomite layers are often characterized by nearly monospecific assemblages of the pelagic diatom Thalassiothrix antarctica, indicating very high primary productivity as IRD grains fell. Diatom-filled fecal pellets with clusters of barite grains are also documented within some of these laminae, further indicating direct mass sinking of diatom mats. Melting icebergs release soluble nutrients along with IRD; thus the coincidence of IRD and bloom species in Amundsen Sea sediments provides compelling evidence that iceberg discharge and melting directly initiates enhanced diatom productivity in the Southern Ocean. These results may contribute to interpreting past WAIS history by providing another proxy for potential collapse events. Furthermore, we suggest that ice sheet collapse may more broadly enhance Southern Ocean diatom production, which in itself can contribute to increased carbon export, potentially attenuating or countering the warming that may have triggered the collapse. 

   more » « less
4. Expedition 382 Preliminary Report: Iceberg Alley and Subantarctic Ice and Ocean Dynamics

   https://doi.org/10.14379/iodp.pr.382.2019  

   Weber, M.E.; Raymo, M.E.; Peck, V.L.; Williams, T. (August 2019, Preliminary report)

   null (Ed.)

   International Ocean Discovery Program (IODP) Expedition 382, Iceberg Alley and Subantarctic Ice and Ocean Dynamics, investigated the long-term climate history of Antarctica, seeking to understand how polar ice sheets responded to changes in insolation and atmospheric CO2 in the past and how ice sheet evolution influenced global sea level and vice versa. Five sites (U1534–U1538) were drilled east of the Drake Passage: two sites at 53.2°S at the northern edge of the Scotia Sea and three sites at 57.4°–59.4°S in the southern Scotia Sea. We recovered continuously deposited late Neogene sediment to reconstruct the past history and variability in Antarctic Ice Sheet (AIS) mass loss and associated changes in oceanic and atmospheric circulation. The sites from the southern Scotia Sea (Sites U1536–U1538) will be used to study the Neogene flux of icebergs through “Iceberg Alley,” the main pathway along which icebergs calved from the margin of the AIS travel as they move equatorward into the warmer waters of the Antarctic Circumpolar Current (ACC). In particular, sediments from this area will allow us to assess the magnitude of iceberg flux during key times of AIS evolution, including the following: • The middle Miocene glacial intensification of the East Antarctic Ice Sheet, • The mid-Pliocene warm period, • The late Pliocene glacial expansion of the West Antarctic Ice Sheet, • The mid-Pleistocene transition (MPT), and • The “warm interglacials” and glacial terminations of the last 800 ky. We will use the geochemical provenance of iceberg-rafted detritus and other glacially eroded material to determine regional sources of AIS mass loss. We will also address interhemispheric phasing of ice sheet growth and decay, study the distribution and history of land-based versus marine-based ice sheets around the continent over time, and explore the links between AIS variability and global sea level. By comparing north–south variations across the Scotia Sea between the Pirie Basin (Site U1538) and the Dove Basin (Sites U1536 and U1537), Expedition 382 will also deliver critical information on how climate changes in the Southern Ocean affect ocean circulation through the Drake Passage, meridional overturning in the region, water mass production, ocean–atmosphere CO2 transfer by wind-induced upwelling, sea ice variability, bottom water outflow from the Weddell Sea, Antarctic weathering inputs, and changes in oceanic and atmospheric fronts in the vicinity of the ACC. Comparing changes in dust proxy records between the Scotia Sea and Antarctic ice cores will also provide a detailed reconstruction of changes in the Southern Hemisphere westerlies on millennial and orbital timescales for the last 800 ky. Extending the ocean dust record beyond the last 800 ky will help to evaluate dust-climate couplings since the Pliocene, the potential role of dust in iron fertilization and atmospheric CO2 drawdown during glacials, and whether dust input to Antarctica played a role in the MPT. The principal scientific objective of Subantarctic Front Sites U1534 and U1535 at the northern limit of the Scotia Sea is to reconstruct and understand how ocean circulation and intermediate water formation responds to changes in climate with a special focus on the connectivity between the Atlantic and Pacific basins, the “cold water route.” The Subantarctic Front contourite drift, deposited between 400 and 2000 m water depth on the northern flank of an east–west trending trough off the Chilean continental shelf, is ideally situated to monitor millennial- to orbital-scale variability in the export of Antarctic Intermediate Water beneath the Subantarctic Front. During Expedition 382, we recovered continuously deposited sediments from this drift spanning the late Pleistocene (from ~0.78 Ma to recent) and from the late Pliocene (~3.1–2.6 Ma). These sites are expected to yield a wide array of paleoceanographic records that can be used to interpret past changes in the density structure of the Atlantic sector of the Southern Ocean, track migrations of the Subantarctic Front, and give insights into the role and evolution of the cold water route over significant climate episodes, including the following: • The most recent warm interglacials of the late Pleistocene and • The intensification of Northern Hemisphere glaciation. 

   more » « less
5. Iceberg Alley and Subantarctic Ice and Ocean Dynamics

   https://doi.org/10.14379/iodp.proc.382.2021  

   Weber, M.E.; Raymo, M.E.; Peck, V.L.; Williams, T. (May 2021, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   International Ocean Discovery Program Expedition 382, Iceberg Alley and Subantarctic Ice and Ocean Dynamics, investigated the long-term climate history of Antarctica, seeking to understand how polar ice sheets responded to changes in insolation and atmospheric CO2 in the past and how ice sheet evolution influenced global sea level and vice versa. Five sites (U1534–U1538) were drilled east of the Drake Passage: two sites at 53.2°S at the northern edge of the Scotia Sea and three sites at 57.4°–59.4°S in the southern Scotia Sea. We recovered continuously deposited late Neogene sediments to reconstruct the past history and variability in Antarctic Ice Sheet (AIS) mass loss and associated changes in oceanic and atmospheric circulation. The sites from the southern Scotia Sea (Sites U1536–U1538) will be used to study the Neogene flux of icebergs through “Iceberg Alley,” the main pathway along which icebergs calved from the margin of the AIS travel as they move equatorward into the warmer waters of the Antarctic Circumpolar Current (ACC). In particular, sediments from this area will allow us to assess the magnitude of iceberg flux during key times of AIS evolution, including the following: • The middle Miocene glacial intensification of the East Antarctic Ice Sheet, • The mid-Pliocene warm period, • The late Pliocene glacial expansion of the West Antarctic Ice Sheet, • The mid-Pleistocene transition (MPT), and • The “warm interglacials” and glacial terminations of the last 800 ky. We will use the geochemical provenance of iceberg-rafted detritus and other glacially eroded material to determine regional sources of AIS mass loss. We will also address interhemispheric phasing of ice sheet growth and decay, study the distribution and history of land-based versus marine-based ice sheets around the continent over time, and explore the links between AIS variability and global sea level. By comparing north–south variations across the Scotia Sea between the Pirie Basin (Site U1538) and the Dove Basin (Sites U1536 and U1537), Expedition 382 will also deliver critical information on how climate changes in the Southern Ocean affect ocean circulation through the Drake Passage, meridional overturning in the region, water mass production, ocean–atmosphere CO2 transfer by wind-induced upwelling, sea ice variability, bottom water outflow from the Weddell Sea, Antarctic weathering inputs, and changes in oceanic and atmospheric fronts in the vicinity of the ACC. Comparing changes in dust proxy records between the Scotia Sea and Antarctic ice cores will also provide a detailed reconstruction of changes in the Southern Hemisphere westerlies on millennial and orbital timescales for the last 800 ky. Extending the ocean dust record beyond the last 800 ky will help to evaluate dust-climate couplings since the Pliocene, the potential role of dust in iron fertilization and atmospheric CO2 drawdown during glacials, and whether dust input to Antarctica played a role in the MPT. The principal scientific objective of Subantarctic Front Sites U1534 and U1535 at the northern limit of the Scotia Sea is to reconstruct and understand how intermediate water formation in the southwest Atlantic responds to changes in connectivity between the Atlantic and Pacific basins, the “cold water route.” The Subantarctic Front contourite drift, deposited between 400 and 2000 m water depth on the northern flank of an east–west trending trough off the Chilean continental shelf, is ideally situated to monitor millennial- to orbital-scale variability in the export of Antarctic Intermediate Water beneath the Subantarctic Front. During Expedition 382, we recovered continuously deposited sediments from this drift spanning the late Pleistocene (from ~0.78 Ma to recent) and from the late Pliocene (~3.1–2.6 Ma). These sites are expected to yield a wide array of paleoceanographic records that can be used to interpret past changes in the density structure of the Atlantic sector of the Southern Ocean, track migrations of the Subantarctic Front, and give insights into the role and evolution of the cold water route over significant climate episodes, including the following: • The most recent warm interglacials of the late Pleistocene and • The intensification of Northern Hemisphere glaciation. 

   more » « less