Winter sea ice and snow mass balance from repeated transects in MOSAiC Central Observatory

Abstract:

Sea ice thickness and snow depth from repeated transects by GEM-2 electromagnetic sensor and Magnaprobe snow depth sonde are the backbone of distributed in-situ mass balance measurements. In combination with the calibration drillings these are the only extensive direct measurements and as such essential complimentary information required for interpretation and extrapolation of other ice and snow observations (e.g. surface elevation, ice draft, snow pits, temperature profiles, various airborne and remote sensing observations), ocean and atmosphere surface fluxes and finally also ecosystem and bio-geochemistry parameters of sea ice. Here, we focus on the data from two core transects of two distinct sea ice types that were revisited near-weekly between October 2019 and May 2020 in the MOSAiC Central Observatory (CO). In total, there were 23 and 16 such transects at both locations, each with a total length of approximately 1.5 km (depending on accessibility and deformation). The spatial resolution of the total snow and ice measurement bellow 0.1 m with a ~4 m footprint and point measurements of snow depth with 1.5 m mean spacing result in a gridded product with resolution of 1-5 m along the transect lines. We also compare the measurements from these core transects with more opportunistic sampling at other locations with purely level ice or ridges, purely first-year ice (FYI) and even a long transect out of the CO. Our preliminary results show that level ice thickness of second-year ice (SYI) and FYI becomes similar already early in the winter. The snow depth exhibits large spatial and temporal heterogeneity with mobile snow bedforms on level ice and maximum depth values in the areas with deformed sea ice. Incidentally, the mean snow depth hardly changes after the initial build-up, but significant amounts of snow accumulate in the pressure ridges. In perspective, our data will allow us to explore the expected negative correlation between local snow depth and ice thickness on level ice and will become a precious dataset for validation of mass balance and heat fluxes in numerical models of snow and sea ice.