North American Meltwater Routing to the North Atlantic During the Last Deglaciation

J.T. Teller (University of Manitoba, Dept. of Geological Sciences, Winnipeg, Canada, R3T 2N2); J. Licciardi and P.U. Clark (Geosciences, Oregon State University, Corvallis, OR 97331)

Freshwater runoff from North America has been implicated in altering ocean circulation and global climate during the last deglaciation. Meltwater from the retreating Laurentide Ice Sheet and precipitation runoff was routed through a complex and changing network of cryohydrological basins that frequently underwent abrupt amalgamations and subdivisions. Using a new reconstruction of the Laurentide Ice Sheet during the last deglaciation (Licciardi et al., 1998, Quat. Sci. Rev.), precipitation fields from NCAR CCM1, and new reconstructions of the linkages and routing history of 28 cryohydrological basins between 18 and 8 ka (radiocarbon) , we have calculated the freshwater fluxes to the North Atlantic and Arctic Oceans through 4 main routes: Mississippi to Gulf of Mexico, St. Lawrence to North Atlantic, Hudson Strait to the Labrador Sea, and Mackenzie and Arctic rivers to the Arctic Ocean. Results show that significant changes in freshwater fluxes to the North Atlantic by way of more northerly (i.e., St. Lawrence) versus more southerly (i.e., Gulf of Mexico) routes occurred on century-to-millennial timescales as a result of opening and closing of drainage routes associated with advances and retreats of the ice- sheet margin. These changes in freshwater fluxes are of the order suggested by ocean models to have affected rates of thermohaline circulation in the North Atlantic during the last deglaciation.