Elevation change and ice flow at Horseshoe Valley, Patriot Hills, West Antarctica
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Patriot Hills is located at 80 degrees 18'S, 81 degrees 22'W, at the southernmost end of the Heritage Range, Ellsworth Mountains, West Antarctica. A comparison of glacier elevation data and ice velocities obtained by the differential global positioning system in the period 1996-97 is presented. Ablation/ accumulation rates measured at a network of stakes in Horseshoe Valley show average accumulation of 70 kg m(-2) a(-1) in the central part of the valley, and a maximum ablation of -170 kg m(-2) a(-1) at the edge of the blue-ice area, close to Patriot Hills. Changes in the surface elevation of the glacier measured at 81 stakes in the period 1995-97 show a mean thickening of +0.43 +/- 0.42 m a(-1), which, considering the uncertainties, indicates that the ice sheet around Patriot Hills is in near steady state. Surface velocities, in combination with ice thicknesses obtained by ground-based radio-echo sounding, are used to compute the ice flux across the Horseshoe Valley transect. A total outflow of 0.44 +/- 0.08 km(3) a(-1) is obtained. Considering a catchment area for Horseshoe Valley of 1087 km(2) upstream from the flow transect, and a net accumulation rate of 100 kg m(-2) a(-1), a total input of 0.11 +/- 0.04 km(3) a(-1) by snow accumulation is obtained. Accepting a near-equilibrium condition for the ice sheet, the flux difference, i.e. 0.33 km(3) a(-1), must be supplied by flow from the inland ice sheet through ice cliffs located in mountain gaps in the Heritage Range. If Horseshoe Valley is not in steady state but is thickening, the positive mass balance could be due to increased snow accumulation or enhanced ice flow from the interior of the ice sheet. New data are needed to elucidate this.