Project:


Glacial isostatic adjustment


Project leader:
Georg Kaufmann

Project members:
Holger Steffen, Berlin, Germany
Kurt Lambeck, Canberra, Australia
Patrick Wu, Calgary, Canada

Institutions involved:
Institut für geologische Wissenschaften, FU Berlin, Germany
Research School of Earth Sciences, ANU, Australia
Dept. of Geology and Geophysics, University of Calgary, Canada

Keywords:
Glacial Isostasy; Ice Ages; Earth's Mantle; Geodynamics; Rheology

Start:
2002-2008

Funding:
DFG grant KA1723/1-1
DFG grant KA1723/1-2

Summary:
Large ice sheets have growth repeatedly on the Earth's surface during the glacial phases of the current ice age. Each growth phase of ice sheets, lasting for about 110,000 years, was complemented by a drop in sea level of around 100-130 meters. Melting of the large ice sheets then happened within a considerably shorter time interval of roughly 10,000 years.

These global, large-scale mass redistribution on the Earth's surface induced glacial isostatic deformations of the Earth's crust and mantle. The deformations are characterised by an instantaneous elastic response, and a time-dependent viscous relaxation, the latter being controlled by the viscosity of the Earth's mantle. Altough today we are well into an interglacial period, the last large ice sheet complexes vanished around 8,000 years ago, the viscous relaxation of the Earth can still be observed.

Numerious observations document the global response of crust and mantle to the ice-age mass exchanges: Paleo-coastlines, which can be found above present sea level in areas formerly glaciated, or submerged below sea level in areas far away from former paleo-ice sheets. Present-day crustal deformation rates in formerly glaciated areas, monitored by tide gauges and GPS are another spectacular reminder of the last ice age. Also, changes in the Earth's graviational field and its rotation contain a significant glacial signal, which is controlled by the ongoing viscoelastic deformation of the Earth.

The observations related to glacial isostatic adjustment can be inverted in terms of the viscosity structure of the Earth's mantle. Here, our project aims at: (i) Refining the observational evidence of glacial isostatic adjustment; (ii) Refining of paleo-ice models describing the last glacial cycle; (iii) Inverting the observational data to obtain a reliable estimate of mantle viscosity.