Mountain glaciers during the Late Glacial and Holocene in Arctic Norway 

Abstract

<p>The accelerated melting of ice in the polar regions suggests that the cryosphere is edging towards an irreversible tipping point. How unusual is this trend of ice loss within the frame of natural variability, and to what extent can it be explained by underlying climate dynamics? The SHIFTS project aimed to provide a new avenue for understanding how bi-polar climate varied during the Late Glacial and the Holocene by reconstructing primary features of atmospheric circulation and variability by using glaciers as climate indicators for both northern and southern hemisphere. In north, on the west coast of Troms and Finnmark we have mapped and sampled glacier forelands for cosmogenic dating. These results are combined with an extensive lake coring program targeting lakes with and without glacial input in Arctic Norway. At the Island of Arnøy, western Finnmark we mapped a glacier foreland to build a cosmogenic nuclide chronology from 71 moraine boulders deposited during the late glacial and the Holocene. Our record suggest that this Arctic Norway record reached its maximum late glacial extent about 14 ka ago, prior to the Younger Dryas. Following considerable retreat through the first part of the YD, glaciers re-stabilized in the mid-YD and showed slower oscillatory retreat through the latter part of the YD. This retreat pattern is confirmed from a lake sediment study at Andøya further south in Northern Norway. The sub-annually reconstruction show a glacier advance during the Intra Allerød cold period and thereafter a gradually retreat towards the end of the Younger Dryas when the glacier again did a re-advance. The results from the reconstructed Arctic glaciers during the late glacial show consistency to the glacier record from the southern hemisphere e.g., at South Georgia, New Zealand and in Patagonia. For the Holocene reconstruction we have used analyses of sediments deposited in distal glacier-fed lakes. We recorded several short-lived glacier advances in the early Holocene followed by a genera glacier retreat between 9000 and 7000 cal. yr BP, interrupted by a glacier advance 8200 years ago. Most glaciers were melted away between 7000 and 5200 cal. years BP. After this the glaciers advanced throughout the “Neoglacial”, until they reached its maximum extent during the “Little Ice Age”. The two “Little Ice Age” moraines in the upper valley of Rødhetta at the Island of Arnøy is dated to 480 and 390 yrs. BP using cosmogenic dating. This overall trend is coherent compared to other glacier reconstructions from Arctic Norway, however variations on multi-decadal time scales are observed that possibly reflect more local climatic changes and/or uncertainties associated with the methods employed in this study.</p>