Glacio-isostatic adjustment in Fennoscandia revisited

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 10 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 mga\.