Numerical assessment of a subglacial lake at Svalbard, Spitzbergen

The likelihood of a subglacial lake beneath Amundsenisen Plateau at Southern Spitzbergen, Svalbard, pointed out by the flat signal within the Ground Penetrating Radar (GPR) remote survey of the area, is justified, here, via numerical simulation. This investigation has been developed under the assumption that the icefield thickness does not change on average, as it is confirmed by recently published physical measurements taken over the past forty years. As consequence, we have considered admissible to assume the temperature and density in-depth profiles, snow and firn layers included, to be stationary. The upper icefield surface and the rocky bed surface are known in detail. By adopting a mathematical numerical model, presented on a recent issue of this journal, based on an unsteady Stokes formulation of the ice flow and a Large Eddy Simulation formulation of the lake water flow, first, we compare two different descriptions of ice water content, in the form of a steady depth dependent function and as solution to the mass transport equation, accounting for local strain heating effect. The last approach, finally selected, leads to 13% improvement of the numerical value of the ice top surface velocity vs. measured one. Furthermore a reduced form of the basal shear stress and normal stress, by making easier the convergence of the iterative solution procedure, allows to obtain physically consistent numerical ice sliding velocity values at the rocky bottom, quite improved in comparison to previous numerical results. After 20000 d (physical time), although the maximum value of water temperature keeps rather low, the numerical simulation shows that metastability is overcome on more than half of the conjectured basin, with a progressive trend in time in support to the subglacial lake existence. By that time, the numerical subglacial lake surface converges to the GPR flat signal spot with tolerance equal to the GPR measuring error. Then numerical simulation results meet quantitatively and qualitatively the fundamental aspects of the conjecture, so that further on-site investigations on the subglacial lake (e.g. drilling operations) appear fully justified.