Late weichselian and early holocene shore displacement in the central Baltic sea

Abstract

The glacial unloading and resulting isostatic land uplift have together with hydro-isostasy, eustatic rise of sea-level and geoidal changes, ruled the shore displacement of Fennoscandia. Within the Baltic basin, periods of damming and shifts of outlet further complicated the shore displacement during the period studied, ca. 12.2-8.4 ka BP. Information on the Baltic history was derived from shoreline observations and studies on sediment cores from lakes formerly directly affected by the Baltic. These cores were analyzed with respect to pollen, diatoms, and lithology to determine sequences of Baltic sediments, and dated by a combination of radiocarbon dates and biostratigraphy. The studied areas of southeastern Sweden, mainly central Gotland and the Oskarshamn area, eastern Småland, display a similar course of shore displacement. The Late Weichselian period shows a regression of a slightly decreasing rate between ca. 12.2 and 10.3 ka BP. Then followed a fast drop (25 m) of the Baltic's water level; the final drainage of the Baltic Ice Lake. During the next ca. 700 years, the Yoldia stage, a regression of ca. 17 m occurred. This period is mainly characterized by freshwater diatoms in the Baltic, but at ca. 10 ka BP there is evidence of a shortlasting (100–150 year) period with brackish water. The Ancylus transgression, of ca. 11 m, began ca. 9.6 ka BP and culminated ca. 9.3 ka BP. It was followed by a fast regression of 8–10 m, thereafter the rate of regression decreased. Shoreline gradients showed that the fastest shoreline tilting occurred around 10 ka BP, thus ca. 2 ka after deglaciation.