A major re-growth of the Scandinavian Ice Sheet in western Norway during Allerød-Younger Dryas

Distinct Younger Dryas (YD) moraines are mapped more-or-less continuously around the Scandinavian Ice Sheet. In most areas there is no evidence to suggest that a glacial re-advance took place during the YD, either because it did not happen or because older deposits have been removed by glacial erosion. In contrast we here present 90 radiocarbon dates from 36 different sites that were overrun by a major ice sheet advance in the area between Hardangerfjorden and Sognefjorden, SW Norway. Thus this region is exceptional for examining the glacial response to the climate shifts across Allerod-YD. The re-growth of the ice sheet in this sector commenced during the Allerod Interstadial. It expanded along 600–800 m deep fjords reaching a thickness of up to 2000 m. We produce time–distance diagrams for two lobes; for both the outermost coast became ice free close to 15 cal ka BP, i.e. at the onset of the Bolling. The Hardangerfjorden Lobe re-advanced during the Older Dryas (14 cal ka BP), an event that was not replicated for the Herdla Lobe farther north. Both lobes reached their most landward position before re-advancing at 13.5–13.0 cal ka and obtained their maximum extent at the very end of the YD, 11.5 cal ka. The late culmination of the advance is accurately dated and differs from most of the Scandinavian Ice Sheet margin where the maximum was reached during early or middle YD. We also present a time–distance diagram from the Last Glacial Maximum to the ice divide showing two-step retreat; fast retreat occurs 21–20 and 11.5–10 cal ka BP separated by a period of almost no net retreat 20–11.5 cal ka BP, which contrasts with much more even retreat in other parts of the Scandinavian Ice Sheet.