Submesoscale frontal dynamics modulate ocean heat transport beneath Antarctic sea ice

Lia Siegelman, Andrew Thompson, Cosme mosneron-dupin, jean-baptiste sallee, Patrice Klein, sahra kacimi

Antarctic sea ice has experienced unprecedented declines in recent years, yet the processes governing the transfer of subsurface ocean heat toward the ice remain poorly understood. Here, sub-kilometer hydrographic observations collected by an instrumented seal reveal intense, intermittent, and bidirectional vertical heat transport beneath sea ice in the East Antarctic marginal ice zone. During a late-summer melt regime, submesoscale frontal dynamics intermittently connect the underlying modified Circumpolar Deep Water (mCDW) reservoir to the mixed layer, producing localized km-scale heat transport events exceeding $1,000$ W m$^{-2}$. A subsequent autumn ice-growth regime exhibits weaker frontal activity and substantially reduced vertical heat transport. These observations suggest that warm mCDW may contribute to Antarctic sea-ice loss not only by delaying winter ice growth, but also by enhancing basal melt during the melt season through km-scale ocean processes.