| Summary: | Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49(2), (2022): e2021GL096216, https://doi.org/10.1029/2021GL096216. 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/m2 over 2006–2012 to 1.63 ± 0.08 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, 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. This study was supported by the National Key Research and Development Program of China (2018YFA0605901), the National Natural Science Foundation of China (41941012; 42076225; 41776192; 41976219; 41706211). S. C. was supported by the Woods Hole Oceanographic Institution Early Career Scientist Fund and the Lenfest Fund for Early Career Scientists. J. Z. was supported by U.S. NSF Grants PLR-1603259, PLR-1602985, and NNA-1927785. M. S. was supported by U.S. ONR Grant N00014-17-1-2545, NSF Grants PLR 1603266 and OPP-1751363 and NOAA Grants NA15OAR4320063AM170 and NA20OAR4320271.
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