THE MAJOR YOUNGER DRYAS GLACIER ADVANCE IN WESTERN NORWAY STARTED ALREADY IN THE ALLERØD - ACCORDING TO SEA-LEVEL CHANGES

Western Norway experienced large changes during the Lateglacial period. The general ice-front recession accompanied by a lowering of the relative sea-level due to glacio-isostatic recovery, were interrupted by a major ice sheet readvance (> 50 km) and a relative sea-level rise (c. 10 m amplitude) (Bondevik & Mangerud 2002; Lohne et al. in prep.). Both the transgression and the glacier advance culminated simultaneously in the very late Younger Dryas (YD). The coincidence of these maxima is striking and according to geophysical modelling the transgression was a result of halting or reversing of the isostatic uplift and rising sea-level caused by the advancing glacier combined with rising global sea-level.

Due to the eroding nature of a glacier it is difficult to date the start of a glacial advance. However, as indicated by geophysical modelling the regional relative sea-level change is tightly connected to the glacier fluctuations. In a detailed sea-level curve from an area adjacent to the YD end moraine south of Bergen, the sea-level fell after the deglaciation (12 500 ¹⁴C BP/14 450 cal yr BP), and reached a low stand at ca. 11 600-11500 ¹⁴C BP/13 400-13 300 cal yr BP (matched to the Cariaco calibration curve). Subsequently the relative sea-level started to rise and, as mentioned, the transgression culminated in the late YD. Hence, the sea-level record suggests significant glacial loading of the lithosphere starting ca. 13 300 cal yr BP, well before the distinct climatic deterioration at the AL/YD transition.

Generally the AL climate in Western Norway was cool and oceanic, with a relatively high precipitation. Chronologically the suggested glacial build-up coincides with the Inter-Allerød Cold Period. Even though this climatic fluctuation is recorded as a minor signal in Western Norway, it may have increased the length of the accumulation season sufficient to exceed the summer melting, resulting in a reactivation of the ice sheet.

References:

Bondevik, S. & Mangerud, J. 2002: A calendar age estimate of a very late Younger Dryas ice sheet maximum in western Norway. Quaternary Science Reviews 21, 1661-1676.

Lohne, Ø. S., Bondevik, S., Mangerud, J. & Schrader, H. in prep.: Calendar year age estimates of Allerød - Younger Dryas sea-level oscillations at Os, western Norway. To be submitted to Journal of Quaternary Science