West Antarctic Ice Sheet dynamics between 1 and 3 Ma from Pb isotopes in ice-rafted feldspar grains

Abstract

Tracing the sources of iceberg-rafted debris (IRD) can provide vital information about the past dynamics of ice sheets. Lead isotopes have previously been applied to IRD for this purpose in northern high latitudes, but in Antarctica they have either been applied to onshore rocks for continental tectonic reconstructions, or to glaciogenic sediments from East Antarctic glaciers or catchments for regional-scale interpretations of subglacial geology or ice dynamics. Higher resolution IRD provenance histories from sites on the West Antarctic margin could provide essential constraints on continental-scale West Antarctic Ice Sheet (WAIS) dynamics since its inception. During hypothesised Plio-/Pleistocene collapses of the WAIS, the source locations of IRD are likely to have changed as ice streams retreated or disappeared entirely. In the extreme case of a full WAIS collapse, an ice-free Trans-Antarctic Seaway may have formed between the islands of the West Antarctic archipelago, allowing East Antarctic-sourced IRD to be deposited on the West Antarctic continental margin in the Amundsen Sea. Here, we use lead isotopes from individual sand-sized feldspar grains to assess the provenance of Late Pliocene‒Early Pleistocene and Last Glacial Maximum IRD in sediment core PC493, from one of the Marie Byrd Seamounts on the western Amundsen Sea continental slope. Early results from a comparison of Pb isotope data on down-core feldspar grains to those on Holocene grains at site PC493 indicate a largely unchanged West Antarctic source for both glacial and interglacial IRD. Analysing more grains at higher stratigraphic resolution will give a more complete indication of IRD source variability and better define clusters and outliers in the data. Future research will be aimed at expanding on these results to constrain the variability of IRD contributions from different sources along the West Antarctic margin through the Plio-/Pleistocene and therefore WAIS stability and its effects on past and future global mean sea level rise.