Paleo Ice Flow Paths from Till Provenance in the Ross Embayment, Antarctica

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

0118455 Farmer This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a collaborative research project to study glacio-marine sediments from the Ross Sea toward an understanding of the history of the West Antarctic Ice Sheet (WAIS). Reliable predictions of the future response of the WAIS to changing climate and rising sea level depend, to a large extent, on improving our knowledge and understanding of its ice dynamics during the last glacial maximum (~18,000 yrs ago). Sediments from the Ross Sea, Antarctica, contain a detailed physical record that can be used to reconstruct past glacier flow patterns. Although significant progress has been made in constraining the extent of ice and the timing of its maximum extent, reconstructions of ice flow paths vary substantially. Studies have predicted that ice streams (regions of fast flowing ice) derived primarily from West Antarctica were dominant features of the Ross Ice Sheet, whereas an ice sheet modeling reconstruction showed roughly equal input from East and West Antarctic ice. Fundamental differences in rock types and ages beneath these source areas should allow the provenance of tills across the Ross Sea to be determined, facilitating the reconstruction of past ice flow paths. Thus the Ross Embayment provides an exciting opportunity to relate modern ice flow dynamics to past ice sheet dynamics and deposits. A detailed provenance study of sediment collected in cores taken from across the Ross Sea floor will be carried out by linking the mineralogical, geochemical, and isotopic characteristics of the sediments from these cores to reference sediments collected from the probable source areas. From these data, the patterns of ice flow across the shelf can be constrained for the last glacial maximum. For this study, existing samples collected from the Ross Sea, and the source areas of East and West Antarctica will be utilized. Composition of the till deposited during the last ice advance will be characterized by examining the sand and pebble size fraction of the sediment, the clay mineralogy, elemental abundance and samarium-neodymium (Sm-Nd) isotopic composition of the silt and clay size fraction. The source of silt and clay fraction may be problematic because of possible mixing of continental and marine sources. This problem will be addressed by determining the composition of modern marine samples which can then be 'subtracted' from the till composition. Samples from the source areas will be analyzed first to determine the compositional fingerprint of each area. Ice flow paths will be determined based on the correspondence between the source areas and the measured values across the Ross Sea. The goal of this project is to characterize both lateral and vertical variations in diagnostic aspects of till mineralogy and isotopic composition in order to make a significant contribution to the understanding of changes in ice sheet dynamics on time scale of the past 30,000 years. Results of this study will allow assessment of the hypothesis that ice streams played a significant role in the most recent disintegration of the WAIS by testing the validity of various ice sheet reconstructions. Additionally, better characterization of the configuration of the Ross Ice Sheet during the last glacial maximum will improve the quality and reliability of models of the past and future characteristics of Antarctic ice sheet behavior.