Development and application of geochemical tracers for paleo and modern oceanography

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The rise in anthropogenic CO2 may alter future climate and we must improve our predictive capabilities to decide on optimal societal responses. The ocean plays a critical role in regulating Earth's climate by controlling atmospheric CO2 and by redistributing incoming solar heat. The distribution of two natural radioisotopes (230Th and 231Pa) in seawater provides important information on particle dynamics, carbon fluxes and deep-water circulation in the modern ocean, which can be used to better quantify oceanic processes important for climate change. In addition, the incorporation of these isotopes in the sedimentary record provides a means of assessing the temporal evolution of these oceanic processes in relation to past climate changes and provides the needed temporal context to distinguish between climatic trends induced by anthropogenic activities and recurring natural cycles.I will measure detailed water column profiles of 230Th and 231Pa dissolved in seawater and associated with marine particles in the northeastern and equatorial Pacific which will complement on-going work in the northwestern Atlantic. These profiles will bring quantitative information on ventilation (Atlantic) and upwelling (Pacific) rates of deep water, and on the factors controlling the sinking rates of marine particles and the sequestration of carbon into the deep sea.This information will be placed in a larger temporal context using the sedimentary record of 230Th and 231Pa to further document changes in carbon flux and deep-water circulation associated with climatic shifts during the late Quaternary and the Holocene. Atlantic sediments provide insights into past changes in deep water formation and their role in triggering abrupt climate changes (work funded by CFCAS). I will complement this study by integrating the 230Th, 231Pa, and foraminifera Mg/Ca in a multi-PIs, multiproxy study of past changes in the circulation and productivity of the Pacific Ocean.