Improved Glacial Isostasy and Associated Sea Level Estimates for Antarctica and NW-Europe
IPGP - Campus Jussieu
Séminaires généraux de l’IPGP
The glacial history of Antarctica during the most recent Milankovitch cycles is poorly constrained relative to the Northern Hemisphere. As a consequence, the contribution of mass changes in the Antarctic ice sheet to global sea-level change and the prediction of its future evolution remain uncertain. The process of Glacial Isostatic Adjustment (GIA) represents the ongoing response of the solid Earth to Late-Pleistocene deglaciation and, therefore, provides information about Antarctic glacial history. Combining ICESat laser altimetry and GRACE gravity data, the GIA contribution can in principle be separated from ongoing ice mass variations. From a 5-year observation period this GIA component is estimated to be 100 ± 67 Gt/yr. We also reasses the potential contribution to regional sea level variations from a hypothesized future rapid (time scales of 500 to 2,000 years) collapse of the West-Antartic ice sheet and show the important regional sea level variations that are induced by a combination of the accompanying gravity changes, crustal deformation and polar wander. Estimates of GIA in NW-Europe can be improved by using more realistic regional shallow earth structures and rheologies and by using coupled earth-ice algorithms into the numerical models. This is necessary as input for estimating GIA contributions to past and present-day sea-level variations. A combination of linear and non-linear rheologies has been shown to provide good fits with global relative sea level data, while at the same time improving fits with uplift rates in North America compared to a purely non-linear rheology. We aim to improve on this rheological modeling in a regional finite element model for GIA in Fennoscandia, which takes into account petrological, heatflow and seismic data and laboratory-derived flow laws. Constraints are provided by GRACE monthly gravity fields, future GOCE observations (expected to become available Spring-Summer 2010), BIFROST GPS solutions and regional relative sea level data. We also assess the effects of crustal and asthenospheric low-viscosity zones and show how these might be constrained by means of GOCE.