The formation of Subantarctic Mode Water SAMW in the Southern Ocean plays a key role in the global oceanic uptake and storage of anthropogenic heat and carbon. Wintertime ocean surface heat loss is a dominant driver of Subantarctic Mode Water formation and variability, but wintertime air-sea flux observations in the Southern Ocean are extremely sparse. Recent advances in our understanding of the role of air-sea fluxes in Subantarctic Mode Water Formation from novel ocean observations are summarized here, particularly the role of synoptic atmospheric extreme events, and the drivers of interannual variations in SAMW. These advances in understanding have important implications for variability in Southern Ocean heat and carbon uptake, and can inform future Southern Ocean observing system design. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.
Keywords: Subantarctic Mode Water; air-sea fluxes; mooring time series; ocean observing; water mass formation.