Recent observations of superimposed ice and snow ice on sea ice in the northwestern Weddell Sea

Abstract

Recent low summer sea ice extent in the Weddell Sea raises questions about the contributions of dynamic and thermodynamic atmospheric and oceanic energy fluxes. The roles of snow, superimposed ice, and snow ice are particularly intriguing, as they are sensitive indicators of changes in atmospheric forcing and as they could trigger snow-albedo feedbacks that could accelerate ice melt. Here we present snow depth data and ice core observations of superimposed ice and snow ice collected in the northwestern Weddell Sea in late austral summer 2019, supplemented by airborne ice thickness measurements. Texture, salinity, and oxygen isotope analyses showed mean thicknesses of superimposed and snow ice of 0.11±0.11 and 0.22±0.22m, respectively, or 3% to 54% of total ice thickness. Mean snow depths ranged between 0.46±0.29m in the south to 0.05±0.06m in the north, with mean and modal total ice thicknesses of 4.12±1.87 to 1.62±1.05m and 3.9 to 0.9m, respectively. These snow and ice properties are similar to results from previous studies, suggesting that the ice's summer surface energy balance and related seasonal transition of snow properties have changed little in past decades. This is supported by our additional analyses of the summer energy balance using atmospheric reanalysis data and by melt onset observations from satellite scatterometry showing few recent changes.