Layer thinning heterogeneities within an ice sheet inferred using a strain-induced anisotropic flow model.

Interpretation of climatic records preserved in ice-sheet requires an accurate knowledge of the absolute age and the duration of ice layers as a function of depth. This relation between age, duration and depth depends on the flow history experienced by ice since its deposit on the surface. Usually, for low accumulation site like in Antarctica, this dating relation is inferred using simplified ice flow models and leads to a smooth thinning function as a function of depth. In the case of a dome, the model is generally reduced to a one-dimensional flow model assuming axisymmetric flow around the dome. Recent texture measurements of the EPICA Dome C core have shown that some layers have experienced larger deformation than the adjacent layers. This is supported also by the difficulties encountered to match the EPICA Dome C and Dronning Maud Land time scales. These observations indicate that the polar ice deformation presents spacial heterogeneities and consequently the layers thinning function is certainly less smooth than expected. Possible causes for these layer disturbances, and their implication in terms of dating, are studied with a full- Stokes ice flow model which takes into account the strain-induced anisotropic behavior of ice. The proposed method consists in following a layer which presents different initial material properties, in term of viscosity and/or initial fabric. The resulting thinning functions for different initial material properties are discussed.