A calendar age estimate of a very late Younger Dryas ice sheet maximum in western Norway

Abstract

We have established an accurate chronology in calendar years for the maximum phase of the Younger Dryas (YD) Scandinavian Ice Sheet in western Norway. Glaciomarine silt confidentially identified in shallow marine basins located was 1-2 km distal to a YD ice-marginal delta. Due to the topography of this area, the silt monitors faithfully the period when the ice sheet reached and remained at its maximum position. In these basins the deposition of silt commenced 6–10 cm above the Vedde Ash Bed (ca 10,300 14C yr BP or ca 12,000 cal yr BP). According to calculated sedimentation rates of the deposits, the deposition of silt started, and thus the ice sheet reached its maximum, 300–400 years after the Vedde Ash fall, around 11,600–11,700 cal yr BP. The ice sheet receded from its maximum position simultaneously with the increase of Betula (birch) pollen at the YD/Holocene boundary, ca 11,500 cal yr BP. The duration of the YD glacial maximum of the Scandinavian Ice Sheet in western Norway was only about 100–200 years, and is constrained within the 14C plateau at 10,000 14C yr BP. The YD glacial maximum occurred extremely late in western Norway, later than elsewhere in Scandinavia. The result also demonstrates different response times for different glaciers. Small cirque glaciers farther north in western Norway expanded to their maximum position very early in the YD, whereas the ice cap at Ålfotbreen reached its maximum later, but still before the Vedde Ash fall. The ice sheet reached its maximum well after the Vedde Ash fall, and only 100–200 years before the YD/Holocene boundary.