Sea-level fluctuations imply that the Younger Dryas ice-sheet expansion in western Norway commenced during the Allerod

After the first emergence following deglaciation, relative sea level rose by 10m in western Norway and culminated late in the Younger Dryas (YD). The relative sea-level history, reconstructed by dating deposits in isolation basins. shows a sea-level low-stand between similar to 13 640 and 13 080 cal yr BP, a 10 m sea-level rise between similar to 13 080 and 11 790 cal yr BP and a sea-level high-stand between similar to-11 790 and 11550 cal yr BP. Shortly after the YD/Holocene boundary, sea level fell abruptly by similar to 37 m. The shorelines formed during the sea-level low-stand in the mid-Allergd and during the sea-level high-stand in the YD have almost parallel tilts with a gradient of similar to 1.3 m km(-1), indicating that hardly any isostatic movement has taken place during this period of sea-level rise. We conclude that the transgression was caused by the major re-advance of the Scandinavian Ice Sheet that took place in western Norway during the Lateglacial. The extra ice load halted the isostatic uplift and elevated the geoid due to the increased gravitational attraction on the sea. Our results show that the crust responded to the increased load well before the YD (starting similar to 12 900 cal yr BP), with a sea-level low-stand at 13 640 cal yr BP and the subsequent YD transgression starting at 13 080 cal yr BP. Thus, we conclude that the so-called YD ice-sheet advance in western Norway started during the Allerod, possibly more than 600 years before the Allerod/YD transition. (c) 2007 Elsevier Ltd. All rights reserved.