Conditions Favoring Glacierization and Deglacierization in North America from a Climatological Viewpoint

Abstract

Approaches to paleoclimatic reconstruction on a local-regional scale through synoptic climatology and on a global scale through numerical modeling are discussed. Synoptic climatological considerations indicate the importance of southeasterly flow components for glacierization in Baffin Island, Labrador-Ungava, and Keewatin. It appears that no individual synoptic pattern is responsible for most of the ablation of ice bodies in eastern Baffin Island so that a synoptic climatological approach to deglacierization is likely to be indeterminate.The NCAR global circulation model with modified surface boundary conditions has been used to simulate the circulation at the last glacial maximum in January and July. The input data include the vertical and horizontal extent of ice, albedos relating to snow cover and vegetation distributions, and ocean temperature. Comparisons with control cases for present conditions show weaker jet maxima, but rather stronger low to mid-tropospheric westerly flow in the Northern Hemisphere, than at present for January and stronger upper westerlies in July. The MSL pressure maps, which must be interpreted with care in the vicinity of the ice sheets, are also discussed. The reconstructions provide a starting point on which hypotheses relating to the Wisconsin deglaciation must be based.