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

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 +/- 0.22 m, respectively, or 3% to 54% of total ice thickness. Mean snow depths ranged between 0.46 +/- 0.29 m in the south to 0.05 +/- 0.06 m in the north, with mean and modal total ice thicknesses of 4.12 +/- 1.87 to 1.62 +/- 1.05 m and 3.9 to 0.9 m, 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.

Automated summary

The recent decrease in summer sea ice extent in the Weddell Sea has led to questions about the contributions of dynamic and thermodynamic atmospheric and oceanic energy fluxes. Research findings show that snow depth, superimposed ice, and snow ice play important roles in the ice's energy balance, and their properties have remained relatively constant in the past decades. Additional analyses using atmospheric reanalysis data and satellite observations indicate limited recent changes in the summer energy balance and melt onset.