Two ice mass balance instruments (part of IAOOS7 and IAOOS8 platforms) deployed near 83°N on the same ice floe, documented the evolution of snow and ice conditions in the Arctic Ocean north of Svalbard in Jan-Mar 2015. Frequent profiles of temperature (every 3 hours) and temperature change after 30s and 120s heating (once a day) were recorded. The ratio of the temperature changes after heating provides a proxy for thermal diffusivity. Both instruments documented flooding and snow-ice formation. Flooding was clearly detectable in the simultaneous changes in thermal diffusivity proxy, increased temperature, and heat propagation through the underlying ice. Slush then progressively transformed into snow-ice. Flooding resulted from two different processes; i) after storm-induced break-up of snow-loaded floes for IAOOS8 and ii) after loss of buoyancy due to basal ice melt for IAOOS7. The instrument on IAOOS7 documented basal sea-ice melt over warm Atlantic waters and ocean-to-ice heat flux peaked at up to 400 Wm-2 in winter.

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