Atmospheric variability over the ∼14.7 kyr BP stadial-interstadial transition in the North Atlantic region as simulated by an AGCM

Abstract.

The ECHAM4-T42 atmospheric general circulation model was applied to study the change in atmospheric variability in the North Atlantic region over the ∼14.7 kyr cal BP climatic transition from Greenland Stadial 2a (GS-2a, end of Pleniglacial) to Greenland Interstadial 1e (GI-1e, start Late Glacial). The following three climates are simulated: (1) present-day, (2) GS-2a and (3) GI-1e. We focus on climatic parameters near the Earth's surface (temperature, precipitation and sea level pressure). Results on two different temporal scales are analysed: seasonal and daily. The seasonal fields show that the main change over the 14.7 kyr BP transition occurred in winter. We calculated daily standard deviations of temperature and pressure about the seasonal means and the high-pass filtered (less than six days) variability of pressure. The largest change in atmospheric variability occurred in northwest Europe. Here, the daily temperature variability decreased by 50%, whereas storm activity also decreased substantially. These changes are related to a northward shift of the Atlantic sea-ice margin at 14.7 kyr BP, leading to a northward relocation of the Atlantic storm track. In the GS-2a experiment, a strong storm track was located over northwest Europe, where frequent depressions produced alternations of northerly air flow (below –30 °C) and southerly air flow (close to 0 °C). This strong daily atmospheric variability decreased in GI-1e because the storm track had a SW-NE orientation over the Atlantic towards Iceland. The decrease in atmospheric variability at 14.7 kyr BP probably contributed to landscape stabilization, for instance, through decreasing eolian transport.