PP42B-02
Toward more realistic freshwater forcing experiments of the 8.2 ka event
Thursday, 17 December 2015: 10:35
2012 (Moscone West)
Carrie Morrill, NOAA's National Centers for Environmental Information, Boulder, CO, United States; University of Colorado at Boulder, Boulder, CO, United States, Amy J Wagner, UNC - Wilmington, Wilmington, NC, United States, Ellen Marguerite Ward, Stanford Earth Sciences, Stanford, CA, United States, Bette L Otto-Bliesner, National Center for Atmospheric Research, Boulder, CO, United States and Nan A Rosenbloom, NCAR/CGD, Boulder, CO, United States
Abstract:
The 8.2 ka event is a key test case for simulating the coupled climate response to changes in the Atlantic Meridional Overturning Circulation (AMOC). Most previous model experiments of this event were forced by the drainage of proglacial Lake Agassiz-Ojibway into the Hudson Bay and entering the Atlantic Ocean through the Hudson Strait. This drainage contained enough water to raise global sea level about 0.2 meters or more, but it likely had a short duration on the order of one year. Recent advances in quantifying the meltwater forcing associated with the 8.2 ka event point towards a forcing larger than the drainage of Lake Agassiz-Ojibway, probably involving the collapse of the Hudson Bay ice dome and raising global sea level on the order of 1.5 to 3.0 meters. Using the Community Climate System Model version 3 (CCSM3), we show that this larger forcing yields a better match to paleoclimate proxy records. Despite these improvements in forcing magnitude in model simulations, the forcing itself is still generally applied in an unrealistic geographic manner, across most of the Labrador Sea rather than only along the Labrador coast. We present additional experiments using the CCSM3, with an ocean model resolution only slightly coarser than that used in previous eddy-resolving simulations, to test the sensitivity to freshwater forcing location. When revised freshwater forcing is applied across the Labrador Sea, the AMOC is reduced by about 40% and climate anomalies compare well with proxy records of the 8.2 ka event in terms of magnitude and duration. When the forcing is added only along the Labrador coast, however, most meltwater joins the subtropical gyre and travels to the subtropics with minor impact to the AMOC (about 10% decrease). It is likely that model biases in the placement of the North Atlantic Current remain an important limitation for correctly simulating the 8.2 ka event, though the effects of icebergs or alternative freshwater sources cannot be completely ruled out.
