Neoglacial plateau ice cap behaviour in Central Spitsbergen constrained by subglacially preserved vegetation.

Abstract

Cold-based glacial ice is well known to preserve underlying landforms produced by earlier processes but can also preserve pre-existing organic material and vegetated ground. With current rapid climate warming, overall glacier retreat in the Arctic is exposing formerly ice-buried in situ vegetation at the margin of cold-based ice bodies. Radiocarbon dating of this vegetation constrains the timing of advance of ice over the specific location where the vegetation was collected. Widespread sampling, identification, and dating of vegetation emerging from various ice bodies can permit the reconstruction of the conditions and timing of the latest ice advance in a specific region. While this method has been used in a range of places in the North American Arctic, its application elsewhere has hitherto been limited. Here 11 samples of in situ preserved bryophyte patches from the margins of three plateau ice caps are presented: Bassen, Foxfonna, and Frostisen, in central Spitsbergen, Svalbard. While it cannot be stated when their Neoglacial ice growth initiated, we found that Bassen was already advancing between 2.2 and 1.5 cal. ka BP, and Foxfonna and Frostisen between 1.5 and 1.2 cal. ka BP, the ice caps being as large as today already before these periods, implying an earlier onset of the Neoglaciation. All available published data in relation to vegetation buried by glaciers in Svalbard were gathered within the VEGLAS database allowing for a wider comprehension of neoglacial advances in Svalbard. Two main advance phases are identified in this dataset. A first advance between 1650 and 1150 BP, corresponding to the Dark Ages Cold Period, and a second advance between 850 and 500 BP, corresponding to the first half of the Little Ice Age. A high frequency of ice caps not behaving according to these general ice advance phases has been observed, revealing the existence of an unexpected disparity in glacial dynamics for the ice caps present in Svalbard. Reconstructing constraining ages on the timing and style of Late Holocene glacier readvances enables a clearer understanding of cold-based ice cap responses to climate change and can therefore contribute in developing more nuanced projections for future ice caps behaviour.