INFLUENCE OF INSOLATION AND GLACIATION ON ATMOSPHERIC CIRCULATION IN THE NORTH-ATLANTIC SECTOR - IMPLICATIONS OF GENERAL-CIRCULATION MODEL EXPERIMENTS FOR THE LATE QUATERNARY CLIMATOLOGY OF EUROPE

Atmospheric general circulation models have been used to simulate the sensitivity of regional climates to Late Quaternary changes in insolation, ice sheets and atmospheric CO2. Model results for full-glacial conditions (18 ka) show the Atlantic Westerly jet strengthened and shifted south, a corresponding southward shift of the Icelandic low and a strengthening and northward shift of the subtropical anticyclone (STA). A glacial anticyclone developed over the European ice sheet and cold, dry conditions prevailed over much of Europe. The full-glacial climate anomaly for the North Atlantic sector is explained by a combination of low atmospheric CO2 (reducing global surface temperatures) and circulation changes caused by the ice sheets. By the Early Holocene (9 ka) the ice sheets were much reduced while the orbital anomaly was near its maximum, producing midcontinental summer warming and winter cooling and a reduced latitudinal temperature gradient in the northern hemisphere in both seasons. The jet and the Icelandic low were displaced to north of their present position, producing strong onshore flow and mild, wet winters in northern Europe, while the STA was also shifted northwards, producing offshore flow and dry summers in the same region. During the late-glacial transition the effects of insolation and glaciation were antagonistic for some features of the circulation and synergistic for others. The model results suggest palaeoclimatic hypotheses that could be directly tested by comparison with palaeoclimatic data mapped at a synoptic scale.