Biogeochemical linkages between Ice Age climate, ocean productivity, and carbon cycling

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The goal of this research program is to explore the linkages between ocean circulation, marine productivity, and carbon (C) cycling by reconstructing past ocean conditions from paleo-environmental indicators archived in the sedimentary record. Three complementary projects are proposed that will follow the same approach: New biogenic flux, sea-surface temperature, and mode-water proxy data will be generated on deep-sea cores from the southeast (SE) Pacific Ocean, selected for their strategic importance to the research questions and their ability to fill a gap in current knowledge. These new data will be placed within the context of an ongoing global biogenic flux data synthesis that incorporates information on seven indicators of changes in C accumulation and marine phytoplankton abundance, to reconstruct the relative timing of changes in different components of marine productivity. Finally, these data will be used to evaluate carefully designed model sensitivity experiments in which changes in sea-ice cover, iron fertilization, upwelling intensity, and freshwater forcing have been imposed. Simulated changes in productivity will be compared with observed ice age reconstructions to assess which processes provide the best match to the data for the following projects: PROJECT 1 explores the influence of sea-ice cover and dust on silica and C cycling. PROJECT 2 examines the influence of changed Southern Hemisphere circulation (e.g., westerly winds, oceanic fronts, Subantarctic Mode Water formation) on productivity. PROJECT 3 investigates the potential influence of polar surface freshening and associated circulation changes on marine productivity during the transition from the last Ice Age to today. The proposed research will provide new reconstructions of past oceanic conditions in the SE Pacific Ocean during the last Ice Age. The global paleo-environmental datasets benefit the field of Earth System science by providing extensive and highly novel evaluation tools for analyzing ocean biogeochemistry model simulations. The results will contribute to our current knowledge of the ice age ocean C cycle, identifying oceanic mechanisms responsible for ice-age changes in atmospheric carbon dioxide.