On the hydrological cycle under paleoclimatic conditions as derived from AGCM simulations

The atmospheric hydrological cycle is compared for different time slices of the late Quaternary. Simulations have been conducted with an atmospheric c irculation model at T42 resolution, and we have performed a global evaluati on of the atmospheric water vapor transport. The water export from the Atla ntic catchment area, important for driving the large-scale thermohaline oce an circulation, is analyzed in detail. For the Last Glacial Maximum (LGM), we examine the model's sensitivity with respect to tropical cooling relativ e to the CLIMAP reconstruction which is motivated by recent data. We find t hat the LGM experiment with tropical cooling is in better agreement with pr oxy data available. Our experiments indicate that the water vapor transport is strongly affected by three mechanisms: continental drying, eddy moistur e transport, and changes in the tropical circulation. Except for the contin ental drying and the blocking effect of the Laurentide ice sheet, the hydro logical cycle is substancially different for both LGM experiments. We find that the hydrological system is rather sensitive to tropical temperature ch ange which is important to understand paleoclimate and future climate chang es.