Unveiling the provenance of sediments in the moraine complex of Aldegonda Glacier (Svalbard) after glacial retreat using radionuclides and elemental fingerprints

摘要

In the changing glacierized areas of the maritime Arctic region, fluxes of sediments are of high intensity during the Arctic melting season. On the Western Spitsbergen Island around Gronfjord, several glaciers have declined rapidly over the last century. The Aldegonda Glacier has retreated about 2 km since 1911 when the glacier tongue reached the seashore which lead to new exposed surfaces in the proglacial area supplying sediments to the fjord during the arctic summer. We explored if the geochemical signature of sediments can be used to discriminate sediment provenance in proglacial environments during different stages of the melting season. To this purpose a sampling campaign was undertaken in July 2015 in the Aldegonda Glacier area, to obtain 24 composite surface samples of moraine materials and sediments at the glacier surface and 12 sediment mixtures. Fingerprinting techniques were applied to determine the sediment provenance and tracers were selected using a novel conservative index and consensus ranking method. FingerPro model identified bottom moraines as predominant source in all cases (74%), recent moraines amounted to 15% and sediment on ice contributed 11%. Radionuclide signatures were of great value to identify sediment provenance, and Cs-137 and Pb-210(ex) were among the most selected tracers. Variations in source contributions depended on the location and type of the sediment mixtures. Differences in source contributions also varied temporarily suggesting different sediment mobilization processes during snow and ice melt. Snow and ice melt are the main drivers of sediment mobilization contributed from moraines during summer. Moreover, sediments accumulated on the glacier surface including cryoconite, deliver radionuclides and heavy metals associated to fine particles that have an impact on terrestrial and sea arctic ecosystems. Such deleterious impact could be one main effect of climate change on glacierized environments worldwide. (C) 2020 Elsevier B.V. All rights reserved.