Glacial Isostatic Adjustment in Antarctica : a rheological study

 The Antarctic Ice Sheet (AIS) is the largest ice sheet on Earth that has known important mass 
 changes during the last 20 kyrs. These changes deform the Earth and modify its gravity field, 
 a process known as Glacial Isostatic Adjustment (GIA). GIA is directly influenced by the mechanical
 properties and internal structure of the Earth, and is monitored using Global Navigation Satellite 
 System positioning or gravity measurements. However, GIA in Antarctica remains poorly constrained  
 due to the cumulative effect of past and present ice-mass changes, the unknown history of the past
 ice-mass change, and the uncertainties of the mechanical properties of the Earth. The viscous 
 deformation due to GIA is usually modeled using a Maxwell rheology. However, other geophysical
 processes employ Andrade (tidal deformation) or Burgers (post-seismic deformation) laws that could 
 result in a more rapid response of the Earth. We investigate the effect of using these
 different rheology laws to model GIA-induced deformation in Antarctica.  

Employing the ALMA and TABOO softwares, we use the Love number and Green functions formalism to
compute the surface motion and the gravity changes induced by the past and present ice-mass redistributions.
We use the elastic properties and the radial structure of the preliminary reference Earth model (PREM) and the
viscosity profile given by Hanyk (1999). The deformation is computed for the three rheological laws mentioned
above using ICE-6G and elevation changes from ENVISAT (2002-2010) to represent the past and present changes
of the AIS, respectively. 

We obtain that the three rheological laws lead to significant Earth response within a 20 kyrs time interval since
the beginning of the ice-mass change. The differences are the largest between Maxwell and Burgers rheologies
during the 500 years following the beginning of the surface-mass change. Regarding the response to present
changes in Antarctica, the largest discrepancies are obtained in regions with the greatest current melting rates,
namely Thwaites and Pine Island Glacier in West Antarctica. Uplift rates computed twelve years after the end of
the present melting using Burgers and Andrade rheologies are five and two times larger than those obtained
using Maxwell, respectively.