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

Abstract

The five-year PONAM (Polar North Atlantic Margin: Late Cenozoic Evolution) programme was launched by the European Science Foundation in 1989. Its aim was to study the major climate-driven environmental variations in the Norwegian-Greenland (also Nordic) Sea and its continental margins over the last 5 milliion years. The programme has provided substantial new insights into the contrasting behaviour of the ice sheets covering the Svalbard-Barents Sea and East Greenland over the last glacial-interglacial cycle in particular. The highly dynamic Svalbard - Barents Sea Ice Sheet, after reaching the shelf edge during each stadial, almost vanished during subsequent interstadials. By contrast, the East Greenland Ice Sheet showed only minor advances confined to fjord basins or ending on the inner shelf. Although there is a striking correspondence 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 Sheet showed well-defined Middle and Late Weichselian ice advances, whereas the East Greenland Ice Sheet was characterised by a 55 kyr-long period with a relatively stable ice margin located in fjords or the inner shelf. The contrasting behaviour of the two ice sheets is probably linked to the palaeoceanographic circulation pattern in the Polar North Atlantic. East Greenland is under the influence of the cold East Greenland Current, whereas the development and behaviour of ice in the Barents Sea is influenced by the continuous, but highly variable. North Atlantic meridional current system that has resulted in a northward inflow 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 periods 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 glaciations, which were reflected in terrestrial glacial sequences and in deep-sea records of ice-rafted debris. Differences in ice extent and dynamics around the Polar North Atlantic are expressed in the evolution and architecture of its east and west continental margins. The Svalbard-Barents Sea Ice Sheet developed much later than the East Greenland Ice Sheet, in the Late Pliocene as compared with the Middle/Late Miocene. The Svalbard-Barents Sea margin is characterised by major prograding fans, built mainly of stacked debris flows. These fans are interpreted as products of rapid sediment delivery from fast-flowing ice streams reaching the shelf break during full glacial conditions. Such major submarine fans are not found north of the Scoresby Sund Fan off East Greenland, where ice seldom reached the shelf break, sedimentation rates were 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 predominate. In general, the Greenland Ice Sheet has been more stable than those on the European North Atlantic margin, which reflect greater variability in heat and moisture transfer at timescale varying from 100,000 year glacial cycles to millennial-scale fluctuations.