Insights into west Antarctica's geology and late pleistocene ice sheet behaviour from isotopic sedimentary provenance studies

Abstract

A fundamental question in Antarctic glaciology and climate change research is whether the West Antarctic Ice Sheet (WAIS) has experienced complete or partial disintegration during the late Pleistocene. Direct geological evidence for its past evolution is scarce, preventing improved predictions on its future behaviour. To this end, I investigated the provenance of late Pleistocene (1.1 Myrs) to modern detrital marine sediments deposited off West Antarctica using strontium and neodymium isotopic compositions of fine-grained (<63μm) sediments and 40Ar/39Ar ages on ice-rafted (>150μm) hornblende and biotite grains. Bedrock characteristics inferred from the sedimentary records can ultimately be tied to the location of eroding ice through time, and hence constrain ice dynamics in a novel way. My key findings are as follows: 1) isotopic and geochemical fingerprints of seafloor surface sediments in the Pacific sector of West Antarctica are varied enough to distinguish different ice drainage sectors on the continent and interpret the results in terms of varying subglacial geology and sediment transports pathways 2) the provenance of glaciogenic detritus delivered by the Pine Island and Thwaites Glaciers, which drain the WAIS into the Amundsen Sea, are significantly distinct from each other and reveal little to no provenance change since the Last Glacial Maximum 3) the sediment eroded by the WAIS in the Amundsen Sea area fluctuated in composition in pace with eccentricity between 1.1 and 0.2 Ma, but lacks evidence for substantial retreat from the modern ice margin 4) the sediment eroded during the peak of the last interglacial (~130 ka) suggests a significant retreat or even ‘ungrounding’ of the WAIS its Amundsen Sea sector. Overall, my new data show the promise of the approach chosen. Future work, from additional locations and using complementary methods, such as multivariate analysis, is needed to derive a more complete history of the WAIS.