Deglaciation of coastal south-western Spitsbergen dated with in situ cosmogenic ¹⁰Be and ¹⁴C measurements

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 informs predictions of future decay of marine-based ice sheets (e.g. West Antarctica). Records of ice-sheet change are 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 for the most recent deglaciation. We present 46 ¹⁰Be ages from south-western Spitsbergen that, when paired with in situ ¹⁴C measurements (n = 5), constrain the timing of coastal deglaciation following the last glacial maximum. ¹⁰Be and in situ ¹⁴C measurements from bedrock along a ∼400-m elevation transect reveal inheritance-skewed ¹⁰Be ages, whereas in situ ¹⁴C measurements constrain 400 m of ice-sheet thinning and coastal deglaciation at 17.4 ± 1.5 ka. Our in situ ¹⁴C-dated transect, combined with three additional ¹⁰Be-dated coastal sites, show that the south-western margin of the Svalbard–Barents ice sheet retreated out of the Norwegian Sea between ∼18 and 16 ka. In situ ¹⁴C measurements 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.