TRACE ELEMENT DETRITAL PROVENANCE FOR AMUNDSEN SEA OFFSHORE SEDIMENTS ACROSS THE PLIOCENE CLIMATIC OPTIMUM

Understanding the effects of greenhouse gas forcing on ice sheets requires knowledge of the behavior of high-latitude ice and climate in the past. The Pliocene Climatic Optimum (PCO), ~4.5-4.0 Ma, is a recent geological example of climate warming expected in the near future under the worst IPCC scenario. Marine sediment cores recovered by International Ocean Discovery Program Expedition 379 offshore from the Amundsen Sea drainage sector of the West Antarctic Ice Sheet (WAIS) span glacial and interglacial cycles during the PCO. Expedition 379 cores were retrieved from the Resolution Drift, a sediment drift on the continental rise, at two sites, U1532 and U1533. Two major lithofacies were identified in the Pliocene sediments: thin greenish gray heavily bioturbated clast-bearing units, interbedded with thick brownish gray laminated mud. The green-gray bioturbated facies is thought to represent interglacial periods with high biological productivity facilitated by open seas and ice rafted debris delivered to the sediment drift, while the gray laminated muds correspond to glacial periods. Identifying the location of West Antarctic source rocks for terrigenous detritus in the sediments of the Resolution Drift across the PCO can help to constrain the WAIS configuration during glacial-interglacial cycles. We reconstruct changes in sediment provenance during the PCO by reporting geochemical data for the detrital fraction, collected with an Inductively Coupled Plasma Mass Spectrometer, from Hole U1533B. Th/Sc, Zr/Y, Sr/Th, Cr/V, La/Zr, Rb/Sc ratios and Eu/Eu* for the green bioturbated facies are distinct from those of the gray laminated facies. This difference in trace element ratios suggests different sources and possibly different transport paths for detritus deposited in the two dominant sediment units, which is corroborated by clay mineral data from the same samples. Additionally, we compare Eu/Eu*, Th/Sc, Zr/Y, and other ratios to those reported for seafloor samples from the Amundsen Sea sector. The gray laminated units in the U1533B cores are characterized by ratios reported for surface sediments in Pine Island Trough, a major paleo-ice stream trough on the eastern Amundsen Sea Embayment shelf, and the green bioturbated units are characterized by ratios reported for modern seafloor sediments farther offshore.