Description: There is increasing evidence of an elaborate subglacial meltwater network underneath Antarctic ice sheets and that this meltwater has an important impact on the flow dynamics of ice streams. In addition, a growing number swath bathymetry surveys from previous glaciated continental margins shows morphological features indicative of meltwater features in areas of paleo ice streams. Over the last few years several expeditions into the eastern Amundsen Sea have investigated the paleo ice streams connected to the Pine Island and Thwaites Glaciers. Unusually favorable sea ice conditions in early 2009 and 2010 allowed us to acquire high-resolution swath bathymetry over large, coherent areas of the of the Thwaites and Pine Island paleo ice streams. Together with previous collections, these data reveal details of a rough topography on the inner shelf including several deep channels that connect a series of deeper basins. This complex basin and channel network is indicative of meltwater flow beneath the paleo-Pine Island and Thwaites ice streams, along with substantial subglacial water inflow from the east. This meltwater could have enhanced ice flow over the rough bedrock topography. The meltwater features diminish with the onset of linear features north of the basins. Similar features have been observed at several locations of previously glaciated high-latitude continental margins including the Getz trough system in the central Amundsen Sea and Marguerite Bay in the Antarctic Peninsula. This suggests that these features and the processes that created them are common around the margin. A comparison of the different features allows the identification of the dominant processes and the creation of a conceptual model of subglacial meltwater flow and its interaction with the ice and underlying substrate.

Description: The West Antarctic Ice Sheet (WAIS), which is grounded below present-day sea level and, thus, is highly sensitive to climatic changes, is likely to have had a very dynamic history over the last several million years. WAIS collapse would result in a global sealevel rise of 3-5 m over present levels yet little is known of how it has behaved in the past. Large uncertainties exist regarding the chronology, extent, rates, and spatial and temporal variability of past advances and retreats of the WAIS across the continental shelves, particularly in the Amundsen Sea sector, where no drilling has taken place despite the intense interest in the current and potential behavior of the glaciers feeding into the over-deepened Pine Island Bay. These uncertainties are mainly due to the paucity of data from drill core from this sector. We propose a series of drill cores for the Amundsen Sea Embayment shelf, which is unambiguously fed by the WAIS, where seismic data reveal seaward-dipping sedimentary sequences that are estimated to span the time from the pre-glacial conditions, Miocene or older, to the most recent glacial cycle. Our drilling strategy is to target a transect that includes the oldest sedimentary sequences deposited onto bedrock in the south to the youngest sequences in the north of the western and eastern Amundsen Sea Embayment continental shelf. This transect will yield a detailed history of the glacial cycles in the Pine Island-Amundsen Sea region and allow correlations to the glacial history known from the Ross Sea and to global climate records. In addition, deep-water sites on the continental rise of the embayment are selected for recovering continuous records of glacially transported sediments and the details of climatic and oceanographic changes throughout glacial-interglacial cycles. Because so little is known about the stratigraphy on the Amundsen Sea shelf, new drill core will allow a wide range of questions to be addressed, including: (1) What is the history of advance and retreat of the WAIS in this sector and thus its contribution to past sea-level changes in terms of both rate and magnitude? Have sectors of the marine-based WAIS experienced significant collapses? (2) How does this glacial history correlate with periods of climate warming and changes in ocean circulation? How do warm Circumpolar Deep Water (CDW) incursions onto the continental shelf affect the stability of marine-based ice sheet margins? (3) How did the WAIS behave in the middle Pliocene, the last time Earth’s atmosphere contained more than 400 ppm CO2 and when the Arctic was significantly warmer than today? (4) When did the WAIS first expand onto the ASE continental shelf? Was ice sheet expansion related to uplift in neighboring Marie Byrd Land or related to largescale climate trends?

Description: The West Antarctic Ice Sheet (WAIS), which is grounded below present sea level and, thus, is highly sensitive to climatic changes, is likely to have had a very dynamic history over the last several million years. Its collapse would result in a global sea-level rise of 3-5 m over present levels yet the world’s scientific community is not able to predict how it might behave in the future, nor is much known of how it has behaved in the past. The reconstruction and quantification of partial or complete WAIS collapses in the geological past are needed in order to provide necessary constraints for ice sheet models predicting future WAIS behaviour and its potential contributions to global sea-level rise. Large uncertainties exist regarding the chronology, extent, rates, and spatial and temporal variability of past advances and retreats of the WAIS across the continental shelves. These uncertainties are mainly due to the fundamental lack of data from drill core. A series of drill sites are proposed for the Amundsen Sea Embayment shelf where seismic data reveal oceanward dipping sedimentary sequences that span the time from the pre-glacial depositional phase to the youngest glacial periods. Our drilling strategy is to target a transect from the oldest sequences close to the bedrock-basin boundary in the south to the youngest sequences in the north of the western and eastern Amundsen Sea Embayment continental shelf. This transect will yield a detailed history of the glacial cycles in the Pine Island-Amundsen Sea region and allow correlations to the WAIS history known from the Ross Sea. In addition, deep-water sites on the continental rise of the embayment are selected for recovering continuous records of glacially transported sediments and the details of climatic and oceanographic changes throughout glacial-interglacial cycles.