Under this award the PIs will test the hypotheses that reorganization of the oceans overturning circulation during deglaciation released CO2 from the deep sea, thereby accounting for a large part of the deglacial rise of atmospheric CO2. They found that peak opal burial rates occurred around the Southern Ocean and in the eastern equatorial Pacific Ocean during deglaciation. They believe that this is consistent with a reinvigorated ventilation of deep waters at this time and a corresponding increase in supply of dissolved Si to surface waters. Because this occurred during Heinrich Event 1, when North Atlantic Deep Water formation is believed to have collapsed, they infer that the renewal of deep water ventilation was driven by bottom water formation around Antarctica. They propose to test two hypotheses derived from these findings: H1: Increased stratification of the deep ocean during glacial times reduced the supply of dissolved Si to equatorial upwelling regions; and H2: Deep ocean stratification characteristic of glacial boundary conditions broke down during each Heinrich Event. In order to test these hypotheses they will reconstruct opal accumulation rates in Southern Ocean sediments, and evaluate opal fluxes together with changes in the relative abundance of biomarkers diagnostic of certain phytoplankton taxa in equatorial Pacific sediments. They predict that brassicasterol (diatom proxy)/alkenone (coccolithophorid proxy) concentration ratios were lower during the Last Glacial Maximum than during the Holocene in equatorial Pacific sediments. A further prediction is that brassicasterol/alkenone ratios, like opal fluxes, increased during deglaciation, and during each Heinrich event, relative to glacial baseline conditions. They will test these predictions using routine paleoceanographic methods. They hope that this work will lead to more informed predictions about the oceans uptake of anthropogenic CO2 in the future. The work will support the PhD research of a young female Afghani-American.
P:MGGIPAsCore ProgramMG&G May 2005Abstracts
