Deglaciation of a marine-based ice sheet: Late Weichselian palaeo-ice dynamics and retreat in the southern Barents Sea reconstructed from onshore and offshore glacial geomorphology

摘要

Marine and terrestrial datasets (swath bathymetry, 2D and 3D seismic and remote sensing data) are used to map the megascale glacial geomorphology of the southern Barents Sea seafloor, northern Fennoscandia and the Kola Peninsula, giving new insights into the dynamics and behaviour of the Barents Sea Ice Sheet during retreat. The glacial geomorphology indicates clear spatial and temporal variations in ice dynamics, with evidence for both active ice streaming and frozen-bed conditions at the maximum and during deglaciation. A five-stage reconstruction of the Late Weichselian deglaciation is proposed. At the Late Weichselian maximum, ice covered the whole of the Barents Sea shelf and the configuration and dynamics of the ice sheet were controlled by the Bjornoyrenna (Bear Island Trough) Ice Stream. This was fed by source areas in the central and north-eastern Barents Sea and in the Fennoscandian mainland. Deglaciation was initiated along the western continental margin. Available dating results show that this occurred after 19 cal ka BP. The Bjornoyrenna Ice Stream retreated rapidly (ice margin retreat rates of similar to 275 m a(-1)), but was periodically grounded, as evidenced by a well-developed series of grounding zone wedges. This was followed by an advance of two short-lived ice streams from the eastern sector of the ice sheet into the south-western Barents Sea. These ice streams advanced and retreated very rapidly with no evidence for ice margin standstills. Correlation to dated cores suggests an age of around 16 000 cal ka BP for this readvance. The period of operation of these two ice streams was coincident with maximum ice extent along the eastern margin in Russia. The western Barents Sea ice margin then retreated onshore, with deglaciation continuing at a reduced rate. The initiation of deglaciation coincided with rising global eustatic sea level. Acceleration of calving, due to grounding line floatation rapidly opened up a major calving bay in Bjornoyrenna, encouraging rapid loss of the marine-based ice. The retreat rate stabilised only once the ice sheet retreated onshore, and calving ceased. We note that the observed pattern of rapid retreat, with high variability in ice streaming for the marine-based Barents Sea Ice Sheet, is similar to that of the marine-based sectors of the Late Weichselian British, Laurentide and West Antarctic Ice Sheets.