Geochemical and Petrographic Signatures from Marie Byrd Land and Larsen-B Ice Shelf Sediments : Implications for Provenance Tracing

The goal of this study is to trace ice rafted debris in the Southern Ocean back to its most probable terrestrial source from the West Antarctic Ice Sheet (WAIS), East Antarctic Ice Sheet (EAIS), or the Antarctic Peninsula Ice Cap (APIC) in order to identify past ice sheet collapses in the geologic record. The bedrock in these areas have characteristic petrographic and geochemical signatures that are preserved in glacially transported and deposited sediment. These signatures may allow us to identify ice rafted debris and fine-grained sediment that originate from these three areas, which have undergone recent ice shelf retreat and possibly past episodes of ice sheet collapse, respectively. This study involves the determination of characteristic features of nearshore glacial-marine sediment from each source area that are representative of the sub-ice bedrock, which is largely inaccessible. Bulk sediment elemental abundances including major, minor, and trace elements including heavy metals and rare earth elements (REEs) were measured from the \u3c 63 micron fraction. Geochemical data from Marie Byrd Land yield Al/Ti values of 15-21 suggesting an average continental crust source or possibly a mixture of upper continental crust and mafic intrusions. SNd values from samples within Pine Island Bay and near the Thwaites Ice Tongue range from -2.3 to -8.3, which bracket the offshore SNd values reported by Roy et al., 2007. Petrographic data reveals unique signatures in sediment derived from the Getz Ice Shelf and Pine Island Bay. Samples from the Larsen B Ice Shelf yields Al/Ti values of 21-30, suggesting an upper continental crust source. SNd values range from -1.9 to -4.9, which are distinctly different from both the high negative values observed from the central Weddell Sea to the east, and from the low positive values from the northwestern Antarctic Peninsula (Roy et al., 2007). Petrographic data was consistent with exposed outcrops and geochemical data, indicating a mixture of metamorphosed continental crust and volcanic fragments. The results indicate the potential use of geochemical and petrographic signatures as provenance tracers in ice rafted debris layers