Thickness and density of snow-covered sea ice and hydrostatic equilibrium assumption from in situ measurements in Fram Strait, the Barents Sea and the Svalbard coast

Modern satellite measurements of sea-ice thickness are based on altimeter measurements of the difference in elevation between the snow or ice surface and the local sea surface. For retrieval of sea-ice thickness, it is assumed that the ice is in hydrostatic equilibrium, add that the snow load on the ice and the density of the sea ice and sea water are known. This study presents data from in situ sea-ice thickness drillings and snow and ice density measurements from Fram Strait, the Barents Sea and the Svalbard coast, in the European Arctic. The error in the altimetry ice thickness products is assessed based on the spatial variability of now and ice density and snow thickness data. Ice thickness uncertainty related to snow depth was found to be similar to 40 cm (radar altimeter) and similar to 90 cm (laser altimeter), while uncertainty related to ice density is 25 cm for both techniques. The assumption of hydrostatic equilibrium at the scales of the measurements (10-100 m) was found to hold better in the case of level landfast ice near Svalbard than for Fram Strait drift ice, which consists of mixed ice types, where the deviation between the calculated and measured ice thicknesses was on average similar to 0.5 m.