Ocean-to-ice heat flux (OHF) is a key factor in regulating the variability of sea ice mass balance. Our understanding of the basin-wide scales of this variability during winter is, however, lacking. Using surface drifting buoy observations, we show that during winter in the Arctic Ocean’s Canada Basin, basin median OHF increased from 0.26 W/m² over 2006-2012 to 0.49 W/m² over 2013-2018. We find that this is a result of thinner and less-compact sea ice that promotes enhanced winter ice growth, and thus stronger ocean vertical convection and subsurface heat entrainment. In contrast, Ekman upwelling was a second-order contribution which declined over the study period. The enhanced ice growth creates a cooler, saltier, and deeper ocean surface mixed layer. This in turn enhanced the vertical temperature gradient which favors stronger entrainment of subsurface heat. The upwelling region is identified to be a hot spot for subsurface heat release and higher OHF.

ocean-to-ice heat flux