Observations of flooding and snow-ice formation in a thinner Arctic sea-ice regime during the N-ICE2015 campaign: Influence of basal ice melt and storms

Seven ice mass balance instruments deployed near 83 degrees N on different first-year and second-year ice floes, representing variable snow and ice conditions, documented the evolution of snow and ice conditions in the Arctic Ocean north of Svalbard in January-March 2015. Frequent profiles of temperature and thermal diffusivity proxy were recorded to distinguish changes in snow depth and ice thickness with 2 cm vertical resolution. Four 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 breakup of snow-loaded floes and (ii) after loss of buoyancy due to basal ice melt. In the case of breakup, when the ice was cold and not permeable, rapid flooding, probably due to lateral intrusion of seawater, led to slush and snow-ice layers at the ocean freezing temperature (-1.88 degrees C). After the storm, the instruments documented basal sea-ice melt over warm Atlantic waters and ocean-to-ice heat flux peaked at up to 400 W m(-2). The warm ice was then permeable and flooding was more gradual probably involving vertical intrusion of brines and led to colder slush and snow-ice (-3 degrees C). The N-ICE2015 campaign provided the first documentation of significant flooding and snow-ice formation in the Arctic ice pack as the slush partially refroze. Snow-ice formation may become a more frequently observed process in a thinner ice Arctic.