Early Holocene in Gästrikland, east central Sweden: shore displacement and isostatic recovery

Abstract

In Gästrikland in central Sweden, deglaciation took place c. 11 000 cal. a BP. In the present study the shore displacement during the earliest ice‐free period is investigated by the 14C dating of sediment from isolated lake basins. The shore displacement in Gästrikland includes an initial phase (∼500 years) of rapid regression, followed by a slowing of the relative sea level (RSL) fall to a rate similar to that of the remaining Holocene c. 9250 cal. a BP. The Ancylus Lake stage of the Baltic Sea belongs to the analysed interval. The RSL curve and glacial unloading history are used to separate and quantify elements of isostatic uplift. The postglacial uplift is ∼260 m, of which ∼45 m forms a rapid initial rise, which can be treated as qualitatively separate from the later, slower rise. There is considerable glacial unloading just prior to the deglaciation, but calculations suggest that only a small part of this relates directly to the rapid early Holocene rebound: most unloading is transferred either to uplift immediately prior to the deglaciation or to subsequent Holocene or future uplift. The isostatic rise in Gästrikland occurring between the end of the Younger Dryas stadial and the deglaciation, c. 11 500–11 000 cal. a BP, is estimated to be 100–110 m. Observations and estimations are incompatible with a Weichselian maximum ice thickness much smaller that 3000 m. The lack of glacial unloading during the Younger Dryas has a measurable impact on the Holocene isostatic rebound in Gästrikland, reducing it by an estimated 20–25 m.