From mountain top to the deep sea – Deglaciation in 4D of the northwestern Barents Sea ice sheet

Abstract

The timing of the deglaciation of the northern Barents Sea ice sheet (BSIS) documented in terrestrial and offshore records from the Svalbard archipelago is reviewed. We present new cosmogenic nuclide (CN) ages from formerly unexplored inland areas of northern Svalbard to investigate the timing of thinning of past local ice domes. CN data are compared with radiocarbon ages from marine and terrestrial deposits. 10Be isotope CN dates on erratic boulders from interior Svalbard suggest that glacier surfaces in northern and western Svalbard thinned 950–650 m from 26 ± 4 ka and continued over an extended period until 16 ka. Initial ice retreat from the western outer to the inner shelf began at 20.5 ka and in Storfjordrenna southwest of Svalbard around 19–18 ka. Retreat of grounded ice from the northern outer to the inner shelf did not begin before 15.9 ka. We therefore suggest increasing summer insolation and aridification due to atmospheric circulation changes and perennial sea ice cover as the main mechanisms for the ice thinning and grounded ice retreat from the outer shelves before and during the Heinrich 1 event. The frontal position of the grounded ice sheet, however, did not change during several millennia despite further thinning in interior northern Svalbard. The inner shelf areas rapidly deglaciated towards the fjord mouths along the western coasts between 15 and 14 ka and became ice-free before and during meltwater pulse 1a (mwp-1a). The collapse of the ice shelves from the inner shelf towards the fjord mouths and inner fjords occurred on a decadal to centennial time scale based on overlapping radiocarbon ages from marine sediment cores in addition to CN data from erratic boulders in lowlands. We suggest that additional mechanisms must have caused this rapid collapse. Together with reduced moisture supply in the accumulation areas, we assume that subsurface warm Atlantic water masses that reached the western shelf after 17.5 ka may have accelerated debuttressing of the ice shelves in addition to the Bølling warming that kicked in around 15.1 ka due to increased insolation and the global sea-level rise called mwp-1a. Conservative calculations estimate the contribution of only the northwestern part of the BSIS to sea-level rise with 0.0004 cm yr−1 between 26 and 16 ka and 0.02 cm yr−1 in assumed 300 years between 15 and 14 ka.