Field and Laboratory Program to Evaluate Atlantic Intermediate Circulation During the Past 25,000 Years

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In this project, the PIs will study how changes in deep ocean circulation influenced the distribution of heat, nutrients, and carbon within the ocean, and their link to earth's climate and levels of CO2 in the atmosphere. The research will test the hypothesis that the northward flow of Antarctic Intermediate Water (AAIW) in the Atlantic Ocean is linked to its role as a supplier of North Atlantic Deep Water (NADW), which derives from sinking of surface waters at high northern latitudes and then flows southward in the Atlantic. The PIs predict that when NADW fills more of the deep Atlantic, AAIW penetrates farther northward to supply NADW. In contrast, during abrupt cold events when the formation of NADW was disrupted, the northward penetration of AAIW would have decreased. To address this hypothesis, the PIs will collect new sediment cores from the western tropical Atlantic (~8 N) using the new RV Knorr long coring system. Stable isotope and Mg/Ca data from fossil foraminifera will be used to generate time series of water mass tracers from depths spanning all subsurface water masses, including AAIW and NADW. Better knowledge of the history of the distribution of these water masses will provide a clearer understanding of how deep ocean circulation changes influence climate and atmospheric CO2. The broader impact of this research includes the participation of four graduate and one undergraduate students on the cruise. One graduate student will use the new material for thesis research while an undergraduate will develop a website focusing on the cruise and its scientific significance. Data obtained from this project will be archived with the NGDC website and will be included in historical reconstructions used to improve simulations of past ocean circulation and to test the suitability of general circulation models to predict future climate change. The sediment will be available to other investigators.