Abstract
Abstract. The dynamics of Vestfonna ice cap (Svalbard) are dominated by fast-flowing outlet glaciers. Its mass balance is poorly known and affected dynamically by these fast-flowing outlet glaciers. Hence, it is a challenging target for ice flow modeling. Precise knowledge of the basal conditions and implementation of a good sliding law are crucial for the modeling of this ice cap. Here we use the full-Stokes finite element code Elmer/Ice to model the 3-D flow over the whole ice cap. We use a Robin inverse method to infer the basal friction from the surface velocities observed in 1995. Our results illustrate the importance of the basal friction parameter in reproducing observed velocity fields. We also show the importance of having variable basal friction as given by the inverse method to reproduce the velocity fields of each outlet glacier – a simple parametrization of basal friction cannot give realistic velocities in a forward model. We study the robustness and sensitivity of this method with respect to different parameters (mesh characteristics, ice temperature, errors in topographic and velocity data). The uncertainty in the observational parameters and input data proved to be sufficiently small as not to adversely affect the fidelity of the model.
Highlights
Svalbard is an Arctic archipelago at around 80◦ N
The Vestfonna (VSF) ice cap was the focus of a recent IPY project (Pohjola et al, 2011b, and references therein) with several glaciological fieldwork programs focused on establishing the mass balance, identifying flow dynamics, remote sensing, snow chemistry and paleo ice sheet reconstruction
A Neumann condition at the surface represents the case where the surface velocity is freely determined from the ice geometry, basal friction parameter, etc., whereas the Dirichlet condition constrains the model according to the measured ice velocities
Summary
Svalbard is an Arctic archipelago at around 80◦ N. We use the variational approach with a Robin inverse method proposed by Arthern and Gudmundsson (2010); Gudmundsson (2011) and subsequently used in simulations of Variegated Glacier and the Greenland ice sheet (JayAllemand et al, 2011; Gillet-Chaulet et al, 2012) This algorithm can be implemented numerically without developing an adjoint model, but rather using the normal forward solution of the Stokes equations. We present the results obtained with the Robin method and compare them with results of a simpler approach: the use of mutually varying, but constant, sliding coefficients in different predefined areas This emphasizes the role of the particular basal conditions at every outlet glacier of the ice cap.
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