Influences of changing sea ice and snow thicknesses on simulated Arctic winter heat fluxes

In the high-latitude Arctic, wintertime sea ice and snow insulate the relatively warmer ocean from the colder atmosphere. While the climate warms, wintertime Arctic surface heat fluxes remain dominated by the insulating effects of snow and sea ice covering the ocean until the sea ice thins enough or sea ice concentrations decrease enough to allow for direct ocean-atmosphere heat fluxes. The Community Earth System Model version 1 Large Ensemble (CESM1-LE) simulates increases in wintertime conductive heat fluxes in the ice-covered Arctic Ocean by similar to 7-11 W m(-2) by the mid-21st century, thereby driving an increased warming of the atmosphere. These increased fluxes are due to both thinning sea ice and decreasing snow on sea ice. The simulations analyzed here use a sub-grid-scale ice thickness distribution. Surface heat flux estimates calculated using grid-cell mean values of sea ice thicknesses underestimate mean heat fluxes by similar to 16 %-35 % and overestimate changes in conductive heat fluxes by up to similar to 36 % in the wintertime Arctic basin even when sea ice concentrations remain above 95 %. These results highlight how wintertime conductive heat fluxes will increase in a warming world even during times when sea ice concentrations remain high and that snow and the distribution of snow significantly impact large-scale calculations of wintertime surface heat budgets in the Arctic.