Oceanic freshwater transport during the Last Glacial Maximum

Abstract

Annual mean freshwater transports during the last ice age are calculated using data from a global atmospheric general circulation model. The atmospheric model is used to simulate the climate of 18,000 years ago using Climate: Long‐Range Investigation, Mapping, and Prediction data for the model's seasonally varying sea surface temperatures, ice coverage, and surface topography. The water transports are calculated for each ocean basin using the model's evaporation, precipitation, and runoff. For the present climate, the model's glacial ice sheets and the global water budget are near equilibrium. For the ice age the model does not maintain the glacial ice sheets at steady state but causes them to melt; therefore we reduced the runoff from melting ice to bring the global water budget into equilibrium. Recent studies have shown that salinity anomalies in the North Atlantic caused by changes in the freshwater transport could change the thermohaline circulation. For the present climate the evaporation exceeds the sum of precipitation and runoff in the Atlantic Ocean which leads to a higher mean salinity in the Atlantic than in the Pacific Ocean. The results suggest that this water budget reversed in the Atlantic during the last ice age. This conclusion, however, cannot be stated firmly because the model's global water budget was not in equilibrium for the ice age. The model's freshwater transports for the last ice age are compared with those for the present climate, and implications on changes in thermohaline circulation are discussed.