GLACIAL AND OCEANIC HISTORY OF THE POLAR NORTH-ATLANTIC MARGINS - AN OVERVIEW

The five-year PONAM (Polar North Atlantic Margin. Late Cenozoic Evolut ion) programme was launched by the European Science Foundation in 1989 . Its aim was to study the major climate-driven environmental variatio ns in the Norwegian-Greenland (also Nordic) Sea and its continental ma rgins over the last 5 milliion years. The programme has provided subst antial new insights into the contrasting behaviour of the ice sheets c overing the Svalbard-Barents Sea and East Greenland over the last glac ial-interglacial cycle in particular. The highly dynamic Svalbard Pare nts Sea Ice Sheet, after reaching the shelf edge during each stadial, almost vanished during subsequent interstadials. BS contrast, the East Greenland Ice Sheet showed only minor advances confined to fjord basi ns or ending on the inner shelf. Although there is a striking correspo ndence in the timing and duration of the first post-Eemian ice advance in East Greenland and on Svalbard, their chronology and dynamics have been very different since about 65 ka. The Svalbard-Barents Sea Ice S heet showed well-defined Middle and Late Weichselian ice advances, whe reas the East Greenland Ice Sheet was characterised by a 55 kyr-long p eriod with a relatively stable ice margin located in fjords or the inn er shelf. The contrasting behaviour of the two ice sheets is probably linked to the palaeoceanographic circulation pattern in the Polar Nort h Atlantic. East Greenland is under the influence of the cold East Gre enland Current, whereas the development and behaviour of ice in the Pa rents Sea is influenced by the continuous, but highly variable. North Atlantic meridional current system that has resulted in a northward in flow of relatively warm waters of Atlantic origin on the eastern side of the Polar North Atlantic. Of particular interest are the so-called ''Nordway events'' in glacial stages 6 and 4 to 2. These represented p eriods of pronounced inflow of temperate waters from the south and an associated increase in seasonally open waters, providing moisture for ice-sheet growth. The largest of these events ended in major glaciatio ns, which were reflected in terrestrial glacial sequences and in deep- sea records of ice-rafted debris. Differences in ice extent and dynami cs around the Polar North Atlantic are expressed in the evolution and architecture of its east and west continental margins. The Svalbard-Ba rents Sea Ice Sheet developed much later than the East Greenland Ice S heet, in the Late Pliocene as compared with the Middle/Late Miocene. T he Svalbard-Barents Sea margin is characterised by major prograding fa ns, built mainly of stacked debris hows. These fans are interpreted as products of rapid sediment delivery from fast-flowing ice streams rea ching the shelf break during full glacial conditions. Such major subma rine fans are not found north of the Scoresby Sund Fan off East Greenl and, where ice seldom reached the shelf break, sedimentation rates wer e relatively low and sediment transport appears to have been localised in several major deep-sea submarine channel systems. Few debris flows are present and more uniform, acoustically-stratified sediments predo minate. In general, the Greenland Ice Sheet has been more stable than those on the European North Atlantic margin, which reflect greater var iability in heat and moisture transfer at timescale varying from 100,0 00 year glacial cycles to millennial-scale fluctuations. (C) 1998 Else vier Science Ltd. All rights reserved.