"Large Holocene Excursions in Biologic Productivity and Terrigenous Provenance in a High-Resolution Sediment Record From the Palmer Deep, West Antarctica"

Kelly A. Kryc Department of Earth Sciences Boston University Boston, MA 02215 (617) 353-4085 kkryc@bu.edu
Richard W. Murray Department of Earth Sciences Boston University Boston, MA 02215 (617) 353-6532 rickm@bu.edu rickm@bu.edu
Robert B. Dunbar Department of Geological and Environmental Sciences Stanford University Palo Alto, CA 94305 650-725-6830 dunbar@stanford.edu

The Antarctic Peninsula is highly sensitive to climate change. To assess Holocene climate variability in this region, the Ocean Drilling Program recovered ~50 m of laminated sediments from the Palmer Deep. This sequence comprises the first high-resolution, continuous, Holocene sediment record from the Antarctic margin and is also the only ultra-high resolution ODP record in the Southern Hemisphere. We analyzed Si, Al, Ti, P, Ba, biogenic opal, organic C and N, and organic delta13C and delta15N every 2.5 to 10 cm (~8 - 50 years.). Each of these proxies responds to a large climatic forcing initiated between 4500 and 7000 years B.P. Biogenic opal, Corg, and P accumulation rates double ~2,000 years B.P., reaching a maximum ~5,500 to 7,000 years B.P. Opal concentrations are less variable, indicating biosiliceous production increased during the mid-Holocene. 13C/12C in bulk organic matter are high (with values similar to ice-edge bloom products) ~4500 to 7000 years B.P., signifying stronger diatom bloom events during the mid-Holocene. Prior to ~3000 years B.P., delta15N was lower for ~2,000 years, resulting from less complete utilization of photic zone nitrate. The Al/Ti ratio indicates a change in terrigenous composition ~3500 years B.P. suggesting a change in source, weathering style and/or intensity. In addition, cross-spectral analysis of the terrigenous provenance with terrigenous accumulation show that these two parameters are varying in phase with each other. All tracers of productivity and terrigenous provenance exhibit significant variance at periods of ~400, 200, 140, and 70 years. Although the mechanisms forcing mid-Holocene enhancements in productivity and terrigenous supply remain unclear, candidates include greater glacial and sea-ice freshwater influences, reduced wind shear, or changing oceanographic frontal positions. A possible external forcing parameter is solar irradiance, possibly mediated through variability in the polar vortex.