Increasing Winter Ocean‐to‐Ice Heat Flux in the Beaufort Gyre Region, Arctic Ocean Over 2006–2018

Ocean-to-ice heat flux (OHF) is important in regulating the variability of sea ice mass balance. Using surface drifting buoy observations, we show that during winter in the Arctic Ocean's Beaufort Gyre region, OHF increased from 0.76 +/- 0.05 W/m(2) over 2006-2012 to 1.63 +/- 0.08 W/m(2) over 2013-2018. We find that this is a result of thinner and less-compact sea ice that promotes enhanced winter ice growth, stronger ocean vertical convection, and subsurface heat entrainment. In contrast, Ekman upwelling declined over the study period, suggesting it had a secondary contribution to OHF changes. The enhanced ice growth creates a cooler, saltier, and deeper ocean surface mixed layer. In addition, the enhanced vertical temperature gradient near the mixed layer base in later years favors stronger entrainment of subsurface heat. OHF and its increase during 2006-2018 were not geographically uniform, with hot spots found in an upwelling region where ice was most seasonally variable.