Glacial isostatic adjustment and sea level change near Berkner Island, Antarctica

Abstract

The glacial-isostatic adjustment in Iceland resulting from the recent melting of the Vatnajökull ice cap is controlled by the viscosity distribution in the earth's interior and by the details of the melting history. Interpretations of the results of GPS and gravity measuring campaigns in the time interval 1991-2000 and 1992-1999, respectively, by means of laterally homogeneous earth models for the determination of the lithosphere thickness, the asthenosphere thickness and the asthenosphere viscosity have so far been not fully satisfactory. In particular near the ice margin, the fitting of the computed land uplift and gravity change to the observational data was inadequate, which may be related to the neglegt of the Iceland plume in the laterally homogeneous earth models. In the present study, a program package is used for the modelling of the land uplift and gravity change that allows the computation of load-induced perturbations of a Maxwell-viscoelastic, incompressible, self-gravitating, spherical earth model. To simulate the presence of the plume below the Vatnajökull, an axisymmetric viscosity distribution is used, where the plume radius and the plume viscosity are free parameters. Based on seismic results, a 6-km-thick lithosphere is assumed above the plume, which thickens to 35 km in the peripheral region of the plume. The melting history of the Vatnajökull is founded on interpretations of geomorphological and climatological investigations and is simulated by a load co-axial with the plume with parabolic profile and time-dependent radius. The results of the modelling favour a plume radius of ~80 km and a plume viscosity of (0.3-1.0) x 10^{18} Pa s.