A finite-element model for the vicinity of the Dome Fuji with flow-induced ice anisotropy and fabric evolution

A three-dimensional, thermo-mechanically coupled model with induced anisotropy has been developed and applied to the vicinity of Dome F, Antarctica. The model implements the full Stokes equations for the ice dynamics and the system is solved with the finite-element method (FEM) using the open source multi-physics package Elmer (http://www.csc.fi/elmer/). The finite-element mesh for the computational domain has been created with two data sets, the fine resolution data obtained at Dome F (Watanabe and others, 2003) and the coarse resolution data set obtained from the SICOPOLIS grid (Greve, 1997). The fine data set which represent a 60 x 60 km area around the Dome F station have been merged to the coarse data set to create a single domain of about 200 x 200 km size. The mesh consists of a coarse resolution near the boundaries (20 km) and a mesh resolution refinement (up to 500 m) towards the position of the borehole located at the center of the domain. This procedure has been carried out in order to keep the lateral boundaries sufficiently far away from the dome, so that shallow-ice stresses can be prescribed there. At the base, no-slip conditions are assumed and on the surface, the temperature is prescribed to be constant everywhere on the domain. A Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement factor (CAFFE; Placidi and others 2007, Seddik and others 2007) is used for taking into account the flow-induced anisotropy in ice. The flow law is implemented in Elmer by means of second and fourth order orientation tensors that describe the c-axis orientation of the fabric. Similarly, the fabric evolution equation is written in terms of the evolution of the second order tensor, and it is solved inside Elmer with a Discontinuous Galerkin method (Brezzi and others, 2004) using Picard type iterations for the non-linearity. Since the fabric evolution equation also depends on the fourth order orientation tensor, the IBOF (Invariant-Based Optimal Fitting) closure function is used for the computation of its components from the solution of the second orientation tensor (Chung and Kwon 2002, Gillet-Chaullet and others 2005). The simulations have been carried out with a maximum enhancement factor equal to ten. The questions to be investigated are (i) what is the evolution of the fabric over the last glacial cycle, (ii) how does the flow field change with the fabric, (iii) what is the effect of the ice anisotropy at Dome Fuji.