HR: 0800h
AN: PP21B-1560    [Abstracts]
TI: Variability in Deep Subarctic Pacific Oxygen Concentration Over the Past 150 ka.
AU: * Jaccard, S
EM: jaccard@erdw.ethz.ch
AF: D-ERDW, ETH Zurich, Sonneggstr. 5, Zurich, CH-8092 Switzerland
AU: Haug, G H
EM: haug@gfz-potsdam.de
AF: GFZ, Potsdam, Telegrafenberg, Potsdam, D-14473 Germany
AU: Sigman, D M
EM: sigman@princeton.edu
AF: Department of Geosciences, Princeton University, Guyol Hall, Princeton, NJ 08544 United States
AU: Pedersen, T F
EM: tfp@uvic.ca
AF: SEOS, UVic, Elliott 166, Victoria, BC V8W 3P6 Canada
AU: Francois, R
EM: rfrancoi@eos.ubc.ca
AF: EOS, UBC, 6270 University Rd., Vancouver, BC V6T 1Z4 Canada
AU: Dulski, P
EM: dulski@gfz-potsdam.de
AF: GFZ, Potsdam, Telegrafenberg, Potsdam, D-14473 Germany
AU: Thierstein, H R
EM: thierstein@erdw.ethz.ch
AF: D-ERDW, ETH Zurich, Sonneggstr. 5, Zurich, CH-8092 Switzerland
AB: The subarctic North Pacific represents the end of the global deep ocean circulation pathway, where deep water rises to the subsurface to complete the global thermohaline circulation. Subsurface waters upwelling into the euphotic zone are depleted in oxygen and enriched in dissolved carbon dioxide and macronutrients as a result of constant respiration and remineralization of organic carbon along the routes of abyssal circulation. The subarctic Pacific thus represents a sensitive region to investigate variations in sedimentary redox conditions as a consequence of climate change. Here we present Th-normalized sedimentary redox-sensitive trace metal (Mn, Mo, U) accumulation rates from ODP Site 882 to infer changes in deep North Pacific ventilation across terminations I & II. We couple these observations with submillennial-scale biogenic barium measurements as a proxy for carbon export to separate the influences of deep water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment. Our results suggest that the deep subarctic Pacific water column was close to suboxic conditions during glacial intervals. Authigenic uranium concentrations are significantly higher during cold periods, despite a significant decrease of primary productivity due to a more severe water-column stratification, leaving changes in bottom water oxygenation as the only plausible explanation to account for trace metal enrichment. Molybdenum concentrations in the sediment are not significantly higher than average crustal values, indicating that the water-sediment interface never reached anoxic (i.e. sulfidic) conditions. Simple calculations suggest that glacial oxygen concentration might have been as low as 20-40 μ mol. Ventilation resumed rapidly during deglaciation and remained efficient throughout warm intervals, as indicated by the occurrence of lower authigenic uranium concentrations in the face of higher productivity and carbon flux to the sediment. We propose that the glacial decrease in deep Pacific oxygenation was driven by increased water-column stratification and/or extended sea-ice cover in the Southern Ocean that hindered ocean-atmosphere gas exchange. While the subarctic Pacific was also apparently more stratified during glacial times, the lack of deep ocean ventilation through this region today prevents us from considering it as a driver of the deep North Pacific changes. Our results corroborate previous observations suggesting that the glacial deep Pacific was filled with a very old, corrosive, oxygen-poor water mass.
DE: 4924 Geochemical tracers
DE: 4926 Glacial
DE: 4936 Interglacial
DE: 4962 Thermohaline
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005