Quaternary geology and Paleoclimate


North Atlantic Ocean-Climate Variability in a Warmer World

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MAIN OBJECTIVES: NOCWARM will provide the extended high-resolution proxy reconstructions of ocean state variables necessary to characterize the fundamental behavior of deep ocean circulation and ventilation on multi-decadal to centennial time scales over the current (Holocene) and previous interglacial (MIS 5e) periods. These periods represent the most recent and best characterized, yet distinctly different, examples of warmer-than-present conditions in the North Atlantic. Hence, they offer the possibility to compare and contrast the climate-ocean system behavior under a range of boundary conditions, including many found in simulations of future climate, such as warmer and fresher surface ocean conditions, increased regional radiative forcing, reduced sea ice, and rapid Greenland ice sheet wasting. Utilizing recently recovered sedimentary sequences we will reconstruct past variations in the transport and properties of the lower branches of the Atlantic Meridional Overturning Circulation (AMOC) at key locations in the North Atlantic during the Holocene and MIS5e. Initial results reveal both, 1) that the proposed sedimentary archives and proxies capture multidecadal variability in circulation and deep water properties, and 2) that ocean ventilation in warm climate states is much more variable than previously appreciated. In addition, we will use these same sediments to reconstruct surface ocean hydrographic variability (SST, SSS, and stratification) and determine its phasing relative to deep ocean changes. Together, these constraints will be used to elucidate the relationship between climate and the lower limb of AMOC over a range of timescales and background states. Finally we will synthesize the results with results from ongoing and available transient GCM model experiments, in order to validate model performance and investigate the dynamics of interglacial ocean-climate variability.





NATIONAL PARTNERS: U.S. Ninnemann (Geo), O.H. Otteraa (Uni Research)

INTERNATIONAL PARTNERS: Y. Rosenthal (Rutgers, USA), A. Piotrowski (Cambridge, UK), C. Kissell (LSCE, France)