provenance

Summary The past behavior of the Antarctic ice sheets under different climate conditions to today is a topic that bears directly on the stability of the ice sheets under future global warming. While global ice volume history is broadly known from δ18O in marine sediment records, uncertainties remain, and changes in the geographic extent of the Antarctic ice sheet are not well known. Here we address this deficiency by determining the provenance of Ice-Rafted Debris (IRD) and hence the provenance of the icebergs that carried it, using the isotope geochemical signature of the IRD. ODP Site 1165, 400 km offshore of Prydz Bay, Antarctica, covers the last 20 Ma and is well located to record changes in iceberg provenance over this time. The potential sources of icebergs, Prydz Bay and the coast to the east, have been found to have distinct neodymium and argon isotopic signatures (Roy et al., submitted, van de Flierdt et al., in press). A major provenance change in IRD at Site 1165 is observed between 14 and 7 Ma: before 14 Ma, IRD is locally sourced from the Prydz Bay sector, whereas after 7 Ma, roughly half the IRD comes from the Wilkes Land, Adelie Land, and George V Land. This is likely associated with ice expansion on East Antarctica after the mid-Miocene transition. Additionally, an iceberg drift model has been developed to assess the ocean and climate conditions required to produce the IRD provenance observations. The combination of geochemical provenance analyses and iceberg drift modeling show