Sedimentology and Catchment Processes of Lake Bolterskaret, Svalbard

Sammanfattning: Lacustrine sediments are important archives of landscape and climate evolution. Varved sediments offer a high-resolution archive enabling studies on annual and seasonal scale. Understanding the alteration of sedimentation in glacial lakes under a changing climate is important for paleoclimate reconstructions. This study aims at understanding the modern processes that governs sedimentation in a small high Arctic lake as well as studying the alteration of these processes over the last 60 years. This is carried out through geomorphological mapping and analysis of lacustrine sediment cores. This analysis consists of 239+240Pu dating, elemental composition by an ITRAX core scanner, and detailed lithostratigraphic logging on thin sections. This has resulted in a geomorphological map over the catchment and a compiled stratigraphic log of the sediment core. The result of the study shows that Lake Bolterskaret has evolved from a glacial to a non-glacial lake during the latter part of the 20th century. This evolution is detected in the sediment record as a shift in deposition from classic varves to paraglacial varves. This shift is attributed to the retreat of the Ayerbreen glacier resulting in a shift in sediment source from glacial to paraglacial sediments, originating from reworking of the terminal moraine. Two hillsides also act as sources of sediment as mass movement processes transport debris towards the lake. These processes are suggested to affect the variation in thickness and complexity of the varves. The main forcing of this shift is due to the current warming of the Arctic, causing glaciers to retreat. This study contributes to the greater knowledge about imprints of landscape evolution in lacustrine sediment records by highlighting the rapid catchment evolution in Arctic regions and by linking a shift towards paraglacial sedimentation with glacial retreat. The results from this study emphasize that processes governing sedimentation today cannot be assumed to reflect processes which occurred half a century ago.