Early Break-up (~20 ka) of the Norwegian Channel Ice Stream of the Scandinavian Ice Sheet during the Last Glacial Maximum

Thursday, 18 December 2014: 2:25 PM
John Inge Svendsen1, Jason P Briner2, Jan Mangerud3, Anna L C Hughes3, Nicolas E. Young4 and Kristian Vasskog5, (1)University of Bergen, Department of Earth Science, Bergen, Norway, (2)University at Buffalo, Buffalo, NY, United States, (3)University of Bergen, Bergen, Norway, (4)Columbia University of New York, Lamont-Doherty Earth Observatory, Palisades, NY, United States, (5)Bjerknes Centre for Climate Research, Bergen, Norway
New time-slice reconstructions of Eurasian Ice Sheet limits during Marine Isotope Stage 2 reveal that the timing of both maximum ice sheet extent and subsequent retreat were spatially variable. Here we present a new reconstruction of the glacial and climate history during the last deglaciation based on 52 cosmogenic nuclide 10Be exposure ages from glacially transported boulders in southern Norway as well as other available data from moraines, lake basins and offshore seafloor sediments. The new ages indicate that the Norwegian Channel Ice Stream (NCIS), active during the Last Glacial Maximum (LGM ~21 ka), broke up as early as ~20 ka, leaving the islands Utsira and Karmøy (located 250 km up-flow from the LGM ice-margin position) permanently ice free ever since. We postulate that the ice sheet flowed across the Norwegian Channel to Denmark and onto the North Sea Plateau during an early phase of the last glacial, but when the NCIS started to operate this ice supply to the North Sea diminished. The fast flows of the NCIS led to a lowering of the ice surface on the shelf and presumably also a drawdown of the entire ice sheet. We envision a large open bay across the entire northern North Sea by 20 ka, which facilitated rapid calving at the ice front and ice sheet thinning. There is also evidence to suggest that the Eurasian Ice Sheet complex as a whole was in a state of retreat soon after the collapse of the ice stream suggesting a common causal connection. We think the primary forcing mechanism for the early deglaciation was increasing high-northern-latitude insolation. The adjacent coastal areas of the Norwegian mainland remained ice covered for another 4000 years until ~16 ka when the ice margin along the coast started to retreat eastward. This second stage of ice sheet retreat was interrupted by several re-advances. The largest re-advance culminated at the very end of the Younger Dryas stadial period (11.6 ka).