Glacio isostatic adjustment in Fennoscandia revisited

Abstract

The theory of load-induced relaxation of the layered Maxwell half-space is applied to the study of glacioisostatic adjustment in Fennoscandia. The interpretation uses emergence data from Angermanland (Sweden) and uplift-rate data from the Gulf of Bothnia. With mantle viscosity fixed at 10²¹ Pa s, the data can be explained by an earth model characterized by (a) an elastic surface layer of conventional thickness (about 100 km) superimposed on a low-viscosity layer or (b) an elastic surface layer of enhanced thickness (about 200 km) and no low-viscosity layer. Reasons for this ambiguity and possible ways to resolve it in future studies are suggested. The investigation also attempts to interpret the negative free-air gravity anomaly observed over the deglaciated region of Fennoscandia. Either (i) enhanced mantle viscosity below 670 km depth or (ii) a transition zone in viscosity between an elastic surface layer and a viscous mantle is required to predict negative anomalies substantially larger than 3 mgal.