Establishing the pattern of Holocene-LGM changes in sediment contributions from Antarctica to the Southern Ocean

Terrigenous clastic sediments are brought to the ocean from continental sources
via rivers, ice and wind, and distributed within the ocean by surface and deep
currents. By investigating long-lived radioactive decay systems, the sediment
sources can be traced and the geological history of those sources can be
delineated. The sediments deposited along the Antarctic coast represent a
mixture of different lithologies that were incorporated progressively during
glacial transport, and their composition reflects the variety of bedrock
lithologies underlying different sectors of the ice sheet. The different
basement provinces yield distinctive isotopic signatures, and the sediments
deposited in proximal regions of the Antarctic continent contain information
about Antarctic basement ages and its geological evolution.

This project represents a first attempt to document regionally integrated
provenance signals and individual mineral ages of Antarctic sources to the
Southern Ocean. We analyzed (1) Nd, Hf, and Sr isotope ratios and Sm/Nd ratios
of terrigenous sediment from ~40 cores taken near the perimeter of the
Antarctic continent, south of the Antarctic Divergence, and northward into the
Antarctic Circumpolar Current; (2) K-Ar ages of >500 individual detrital
hornblende crystals from a subset of the core samples; and (3) Hf isotope
ratios of Circum-Antarctic Fe-Mn crusts that were previously analyzed for Pb
and Nd isotope ratios (Abouchami and Goldstein, GCA, 1995 and Albarede,
Goldstein Dautel, GCA 1997). The purposes of the terrigenous sediment and
Fe-Mn analyses were (1) to gain a basic understanding of the "crustal
residence ages" of the source terrains, that is, the average amount of time
the material has been part of the continental crust, (2) track their dispersal
into the Antarctic Circumpolar Current based on analyses of samples from south
and north of the Antarctic Divergence during the Holocene and Last Glacial
Maximum (LGM), (3) to investigate the potential contributions of Antarctic
sources to the dissolved Nd and Hf load in the Circum-Antarctic. The hornblende
K-Ar ages were measured in order to (4) generate a thermal history of the
sediment sources to compare with the bulk sediment crustal residence ages.
Thus, the project has aspects that address the geological evolution of
Antarctica as well as global climate change.