Palaeoglaciology of an ice sheet through a glacial cycle:: the European ice sheet through the Weichselian

Abstract

Satellite images provide unique means of identifying large-scale flow-generated lineations produced by former ice sheets. They can be interpreted to reconstruct the major elements which make up the integrated, large-scale structure of ice sheets: ice divides; ice streams; interstream ridges; ice shelves; calving bays. The evolving palaeoglaciological structure of the European ice sheet during its decay from the Last Glacial Maximum (LGM) is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat. During the retreat phase in particular the time-dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed. Crossing lineations are widespread. The older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum, particularly in areas which lay, during deglaciation, beneath ice divides and inter-ice stream ridges, both areas of slow flow and possibly frozen bed conditions. Four phases of growth (A1 to A4) and five phases of decay (R1 to R5) are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle. The growth and decay patterns are quite different and associated with major shifts in the ice divide, reflecting growth from the Fennoscandian mountains and decay away from marine influenced margins. These patterns were determined by the locations of nucleation areas; spatial patterns of climate; and calving at marine margins.The prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming, and that this might reconcile glaciological models and earth rheology models which infer paleao-ice sheet thickness by inverting sea level data.