Search

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.

The abundant production of in situ cosmogenic 36Cl from potassium renders 36Cl measurements in K-rich rocks or minerals, such as K-feldspars, potentially useful for precisely dating rock surfaces, either in single-nuclide or in multi-nuclide studies, for example combined with 10Be measurements in quartz. However, significant discrepancies in experimentally calibrated 36Cl production rates from spallation of potassium (36PK-sp), referenced to sea-level/high-latitude (SLHL), limit the accuracy of 36Cl dating from K-rich lithologies. We present a new 36Cl calibration using K-feldspars, in which K-spallation is the most dominant 36Cl production pathway (>92% of total 36Cl), thus minimizing uncertainties from the complex multi-pathway 36Cl production systematics. The samples are derived from boulders of an ∼13.4 ka-old landslide in the Swiss Alps (∼820 m, 46.43°N, 8.85°E). We obtain a local 36PK-sp of 306 ± 16 atoms 36Cl (g K)−1 a−1 and an SLHL 36PK-sp of 145.5 ± 7.7 atoms 36Cl (g K)−1 a−1, when scaled with a standard scaling protocol (‘Lm’). Applying this SLHL 36PK-sp to determine 36Cl exposure ages of K-feldspars from 10Be-dated moraine boulders yields excellent agreement, confirming the validity of the new SLHL 36PK-sp for surface exposure studies, involving 36Cl in K-feldspars, in the Alps.