Collaborative Research: Arctic Climate Sensitivity to Freshwater Forcing: Improving Model-Data Comparison of the 8.2 ka Event

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ABSTRACTMorrillOPP-0713951Otto-BliesnerOPP-0713971Intellectual merit: The Principal Investigators will integrate climate modeling and paleoclimate records to better understand the sensitivity of the Arctic climate system to freshening of the North Atlantic. Model projections of future changes in the Atlantic meridional overturning circulation (MOC) have a large spread of values. Because the MOC plays a central role in determining the climate of the circum-North Atlantic, it is essential that we know which, if any, of these models has skill in predicting the response of the MOC. One useful test of the models is to simulate past changes in the MOC, at times when the forcing and response are reasonably well known. One time period, the 8.2 ka event, has been selected as a test case by several modeling groups. This event is observed as an abrupt cool period in circum-North Atlantic paleoclimate records. Its hypothesized cause is the drainage of glacial Lake Agassiz into Hudson Bay, and simulations completed to-date have focused mainly on this forcing. There are, however, other coeval forcings, as well as uncertainties in the methods used to model freshwater fluxes, that have yet to be examined. The PIs will complete three sets of simulations to quantify the importance of these additional forcings and the forcing methodology. These simulations will be completed using the NCAR Community Climate System Model Version 3 (CCSM3). The goal of the first set of simulations will be to compare different methods of freshwater addition, or "hosing." There is no accepted method of hosing and their experiments will allow them to make recommendations for a common methodology. The second set of simulations will systematically investigate the model response to three other freshwater fluxes that occurred in addition to the glacial lake drainage. It is hypothesized that each of these sources played a particular role in generating the ocean and climate response. In the last set of simulations, they will consider the effects of additional atmospheric forcings. These additional forcings have not been previously considered in model experiments, but could have contributed to the climate response. The research will be a first step toward incorporating all significant forcings in a realistic manner in simulations of the 8.2 ka event. This is essential for understanding Arctic climate sensitivity and the ability of coupled climate models to accurately reflect this sensitivity. Broader impacts: Changes in the Atlantic MOC can produce large and rapid climaticperturbations in the circum-North Atlantic and beyond. The proposed research willbenefit society by evaluating our ability to predict future rapid changes associated with freshwater increases in the North Atlantic. The Principal Investigators will participate in synergistic collaborations with other researchers supported by NSF and with scientists worldwide participating in the Paleohosing Model Intercomparison Project. A deliverable of this research will be the model output they generate, archived with the Paleoclimate Modeling Intercomparison Project. The model data will also be available to thescientific community through the NCAR CCSM Paleoclimate Working Group. Thresearch will increase the participation of under-represented groups by including women scientist and a student in the SOARS program at NCAR.