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1. Expedition 374 Scientific Prospectus: Ross Sea West Antarctic Ice Sheet History

   https://doi.org/10.14379/iodp.sp.374.2017  

   McKay, R.M.; De Santis, L.; Kulhanek, D.K. (September 2017, Scientific prospectus)

   null (Ed.)

   Observations from the past several decades indicate that the Southern Ocean is warming significantly and that Southern Hemisphere westerly winds have migrated southward and strengthened due to increasing atmospheric CO2 concentrations and/or ozone depletion. These changes have been linked to thinning of Antarctic ice shelves and marine terminating glaciers. Results from geologic drilling on Antarctica’s continental margins show late Neogene marine-based ice sheet variability, and numerical models indicate a fundamental role for oceanic heat in controlling this variability over at least the past 20 My. Although evidence for past ice sheet variability has been observed in marginal settings, sedimentological sequences from the outer continental shelf are required to evaluate the extent of past ice sheet variability and the role of oceanic heat flux in controlling ice sheet mass balance. International Ocean Discovery Program (IODP) Expedition 374 proposes a latitudinal and depth transect of six drill sites from the outer continental shelf and rise in the eastern Ross Sea to resolve the relationship between climatic/oceanic change and West Antarctic Ice Sheet (WAIS) evolution through the Neogene and Quaternary. This location was selected because numerical ice sheet models indicate that it is highly sensitive to changes in ocean heat flux and sea level. The proposed drilling is designed for optimal data-model integration, which will enable an improved understanding of the sensitivity of Antarctic Ice Sheet mass balance during warmer-than-present climates (e.g., the early Pliocene and middle Miocene). Additionally, the proposed transect links ice-proximal records from the inner Ross Sea continental shelf (e.g., ANDRILL sites) to deepwater Southwest Pacific drilling sites/targets to obtain an ice-proximal to far-field view of Neogene climate and Antarctic cryosphere evolution. The proposed scientific objectives directly address Ocean and Climate Challenges 1 and 2 of the 2013–2023 IODP Science Plan. Drilling Neogene and Quaternary strata from the Ross Sea continental shelf-to-rise sedimentary sequence is designed to achieve five scientific objectives: 1. Evaluate the contribution of West Antarctica to far-field ice volume and sea level estimates. 2. Reconstruct ice-proximal atmospheric and oceanic temperatures to identify past polar amplification and assess its forcings/feedbacks. 3. Assess the role of oceanic forcing (e.g., sea level and temperature) on Antarctic Ice Sheet stability/instability. 4. Identify the sensitivity of the AIS to Earth’s orbital configuration under a variety of climate boundary conditions. 5. Reconstruct eastern Ross Sea bathymetry to examine relationships between seafloor geometry, ice sheet stability/instability, and global climate. To achieve these objectives, we will (1) use data and models to reconcile intervals of maximum Neogene and Quaternary Antarctic ice advance with far-field records of eustatic sea level change; (2) reconstruct past changes in oceanic and atmospheric temperatures using a multiproxy approach; (3) reconstruct Neogene and Quaternary ice margin fluctuations in datable marine continental slope and rise records and correlate these records to existing inner continental shelf records; (4) examine relationships among WAIS stability/instability, Earth’s orbital configuration, oceanic temperature and circulation, and atmospheric pCO2; and (5) constrain the timing of Ross Sea continental shelf overdeepening and assess its impact on Neogene and Quaternary ice dynamics. 

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2. Impacts of ice-shelf melting on water mass transformation in the Southern Ocean from E3SM simulations

   https://doi.org/10.1175/JCLI-D-19-0683.1  

   Jeong, Hyein; Asay-Davis, Xylar S.; Turner, Adrian K.; Comeau, Darin S.; Price, Stephen F.; Abernathey, Ryan P.; Veneziani, Milena; Petersen, Mark R.; Hoffman, Matthew J.; Mazloff, Matthew R.; et al (January 2020, Journal of Climate)

   The Southern Ocean overturning circulation is driven by winds, heat fluxes, and freshwater sources. Among these sources of freshwater, Antarctic sea-ice formation and melting play the dominant role. Even though ice-shelf melt is relatively small in magnitude, it is located close to regions of convection, where it may influence dense water formation. Here, we explore the impacts of ice-shelf melting on Southern Ocean water mass transformation (WMT) using simulations from the Energy Exascale Earth System Model (E3SM) both with and without the explicit representation of melt fluxes from beneath Antarctic ice shelves. We find that ice-shelf melting enhances transformation of Upper Circumpolar Deep Water (UCDW), converting it to lower density values. While the overall differences in Southern Ocean WMT between the two simulations are moderate, freshwater fluxes produced by ice-shelf melting have a further, indirect impact on the Southern Ocean overturning circulation through their interaction with sea-ice formation and melting, which also cause considerable upwelling. We further find that surface freshening and cooling by ice-shelf melting causes increased Antarctic sea-ice production and stronger density stratification near the Antarctic coast. In addition, ice-shelf melting causes decreasing air temperature, which may be directly related to sea-ice expansion. The increased stratification reduces vertical heat transport from the deeper ocean. Although the addition of ice-shelf melting processes leads to no significant changes in Southern Ocean WMT, the simulations and analysis conducted here point to a relationship between increased Antarctic ice-shelf melting and the increased role of sea ice in Southern Ocean overturning. 

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3. Expedition 382 Scientific Prospectus: Iceberg Alley and South Falkland Slope Ice and Ocean Dynamics

   https://doi.org/10.14379/iodp.sp.382.2018  

   Weber, M.E.; Raymo, M.E.; Peck, V.L.; Williams, T. (May 2018, Scientific prospectus)

   null (Ed.)

   International Ocean Discovery Program Expedition 382, Iceberg Alley and South Falkland Slope Ice and Ocean Dynamics, will investigate the long-term climate history of Antarctica, seeking to understand how polar ice sheets responded to changes in atmospheric CO2 in the past and how ice sheet evolution influenced global sea level. We will drill six sites in the Scotia Sea, east of the Antarctic Peninsula, providing the first deep drilling in this region of the Southern Ocean. We expect to recover >600 m of late Neogene sediment that will be used to reconstruct the past history and variability in Antarctic Ice Sheet (AIS) mass loss and associated changes in oceanic and atmospheric circulation. Expedition 382 expects to deliver the first spatially and temporally integrated record of iceberg flux from “Iceberg Alley,” the main pathway by which icebergs are calved from the margin of the AIS and travel equatorward into warmer waters of the Antarctic Circumpolar Current (ACC). In particular, we will characterize the magnitude of iceberg flux during key times of AIS evolution: • The middle Miocene glacial intensification of the East Antarctic Ice Sheet, • The mid-Pliocene warm interval, • The late Pliocene glacial expansion of the West Antarctic Ice Sheet, • The mid-Pleistocene transition, 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 in this region, 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, 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, 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 climate-dust 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 mid-Pleistocene transition. The principal scientific objective of the South Falkland Slope sites to the north 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 South Falkland Slope Drift, a contourite drift on the Falkland margin deposited between 400 and 2000 m water depth, is ideally situated to monitor millennial- to orbital-scale variability in the export of Antarctic Intermediate Water beneath the Subantarctic Front over at least the last 2 My. We anticipate that these sites will 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 and track the migration of the Subantarctic Front. We expect the cored sediments to capture the following significant climate episodes: • The most recent warm interglacials of the late Pleistocene; • The mid-Pleistocene transition, when δ18O records shifted from dominantly 41 to 100 ky periodicity; and possibly • Mid-Pliocene warm intervals, often invoked as the best analog for possible future climate change. 

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4. Highly stratified mid-Pliocene Southern Ocean in PlioMIP2

   https://doi.org/10.5194/cp-20-1067-2024  

   Weiffenbach, Julia E.; Dijkstra, Henk A.; von der Heydt, Anna S.; Abe-Ouchi, Ayako; Chan, Wing-Le; Chandan, Deepak; Feng, Ran; Haywood, Alan M.; Hunter, Stephen J.; Li, Xiangyu; et al (January 2024, Climate of the Past)

   Abstract. During the mid-Pliocene warm period (mPWP; 3.264–3.025 Ma), atmospheric CO2 concentrations were approximately 400 ppm, and the Antarctic Ice Sheet was substantially reduced compared to today. Antarctica is surrounded by the Southern Ocean, which plays a crucial role in the global oceanic circulation and climate regulation. Using results from the Pliocene Model Intercomparison Project (PlioMIP2), we investigate Southern Ocean conditions during the mPWP with respect to the pre-industrial period. We find that the mean sea surface temperature (SST) warming in the Southern Ocean is 2.8 °C, while global mean SST warming is 2.4 °C. The enhanced warming is strongly tied to a dramatic decrease in sea ice cover over the mPWP Southern Ocean. We also see a freshening of the ocean (sub)surface, driven by an increase in precipitation over the Southern Ocean and Antarctica. The warmer and fresher surface leads to a highly stratified Southern Ocean that can be related to weakening of the deep abyssal overturning circulation. Sensitivity simulations show that the decrease in sea ice cover and enhanced warming is largely a consequence of the reduction in the Antarctic Ice Sheet. In addition, the mPWP geographic boundary conditions are responsible for approximately half of the increase in mPWP SST warming, sea ice loss, precipitation, and stratification increase over the Southern Ocean. From these results, we conclude that a strongly reduced Antarctic Ice Sheet during the mPWP has a substantial influence on the state of the Southern Ocean and exacerbates the changes that are induced by a higher CO2 concentration alone. This is relevant for the long-term future of the Southern Ocean, as we expect melting of the western Antarctic Ice Sheet in the future, an effect that is not currently taken into account in future projections by Coupled Model Intercomparison Project (CMIP) ensembles. 

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5. Linearity of the climate system response to raising and lowering West Antarctic and coastal Antarctic topography

   https://doi.org/10.1175/JCLI-D-22-0416.1  

   Pauling, Andrew G.; Bitz, Cecilia M.; Steig, Eric J. (May 2023, Journal of Climate)

   Abstract A hierarchy of general circulation models (GCMs) is used to investigate the linearity of the response of the climate system to changes in Antarctic topography. Experiments were conducted with a GCM with either a slab-ocean or fixed SSTs and sea ice, in which the West Antarctic ice sheet (WAIS) and coastal Antarctic topography was either lowered or raised in an idealizedway. Additional experimentswere conducted with a fully-coupledGCMwith topographic perturbations based on an ice-sheet model in which the WAIS collapses. The response over the continent is the same in all model configurations and is mostly linear. In contrast, the response has substantial non-linear elements over the Southern Ocean that depend on the model configuration due to feedbacks with sea ice, ocean, and clouds. The atmosphere warms near the surface over much of the Southern Ocean and cools in the stratosphere over Antarctica, whether topography is raised or lowered. When topography is lowered, the Southern Ocean surface warming is due to strengthened southward atmospheric heat transport and associated enhanced storminess over the WAIS and the high latitudes of the Southern Ocean. When topography is raised, Southern Ocean warming is more limited, and associated with circulation anomalies. The response in the fully-coupled experiments is generally consistent with the more idealized experiments, but the full-depth ocean warms throughout the water column whether topography is raised or lowered. These results indicate that ice sheet-climate system feedbacks differ depending on whether the Antarctic ice sheet is gaining or losing mass. 

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