Deglaciation of coastal south-western Spitsbergen dated with in situ cosmogenic 10Be and 14C measurements: DEGLACIATION OF COASTAL SOUTH-WESTERN SPITSBERGEN

The Svalbard-Barents ice sheet was predominantly a marine-based ice sheet and reconstructing the timing and rate of its decay during the last deglaciation can inform predictions of future decay of marine-based ice sheets (e.g. West Antarctica). Records of ice-sheet change are now routinely built with cosmogenic surface exposure ages, but in some regions, this method is complicated by the presence of isotopic inheritance yielding artificially old and erroneous exposure ages. Here, we present forty-six 1025 Be ages from bedrock (n = 38) and erratic boulders (n = 8) in southwestern Spitsbergen that, when paired with in situ 1427 C measurements (n = 5), constrain the timing of coastal deglaciation following the last glacial maximum. 10Be and 1428 C measurements from bedrock along a ~400 m elevation transect reveal inheritance-skewed 10Be ages, whereas 1429 C measurements constrain 400 m of ice-sheet thinning and coastal deglaciation at 17.4 ± 1.5 ka. Combined with three additional 10Be-dated coastal sites, we show that the southwestern margin of the Svalbard-Barents ice sheet retreated out of Norwegian Sea between ~18-16 ka. In situ 1432 C measurements can provide key chronological information on ice-sheet response to the last termination in cases where measurements of long-lived nuclides are compromised by isotopic inheritance.