Ostatni lądolód plejstoceński na półkuli północnej

Abstract

Na podstawie najnowszych danych przedstawiono rozmieszczenie i wiek ostatniego lądolodu plejstoceńskiego na półkuli północnej, tj. północnoamerykańskiego i euroazjatyckiego. Przytoczono różne hipotezy dotyczące rozmiarów i pochodzenia lądolodu w strefie arktycznej. Zwrócono uwagę na asynchroniczność maksymalnego zasięgu lądolodu w różnych częściach jego marginalnej strefy.THE LAST PLEISTOCENE CONTINENTAL ICE SHEET IN THE NORTHERN HEMISPHERE The younger part of the last Pleistocene glaciation (Upper Vistulian, Upper Valday, Upper Wisconsin, Upper Devens) was significantly marked by a rapid development of continental ice sheets in the north hemisphere. The two independent continental ice sheets, namely the North-American one and the Euro-Asiatic one (Figs 1-2) originated in that time. Both of them were expanding down from several centers and reached their maximum extents in different times (Figs 3-6). Case of the British Islands was taken in the paper to present the thickness of ice sheet (Fig. 7) in Europe; its development and evidence within the shelf area are clearly shown in Figs 8 and 9.When the last Pleistocene glaciation was subjected to analysis of its main features the following could be deducted: 1. Both the ice sheets, i.e. the North-American and the Euro-Asiatic. developed in the same time. They reached maximum development in their southern parts considerably earlier than in the north. The difference in time amounts to 8 - 10 thousand years. 2. Both the ice . sheets locally oscillated along their extent boundaries. 3. There were many centers (ice domes) within both the continental ice sheets, from which ice was flowing outwards., The centers were shaped in oblong ice-sheds; their location was independent on morphology of subglacial surface and on their relation to a sea level as well. The centres were situated eccentricly to the ice sheet extent limits. 4. Disintegration of the continental ice sheet in the Arctic lasted considerably shorter time than in the south. 5. At the beginning of their disintegration both the ice sheets were already climatic relics.