The Southern Ocean mixed layer and its boundary fluxes: fine-scale observational progress and future research priorities

• Published in: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
• Main Authors: Swart, Sebastiaan, du Plessis, Marcel D., Nicholson, Sarah-Anne, Monteiro, Pedro M. S., Dove, Lilian A., Thomalla, Sandy, Thompson, Andrew F., Biddle, Louise C., Edholm, Johan M., Giddy, Isabelle, Heywood, Karen J., Lee, Craig, Mahadevan, Amala, Shilling, Geoff, de Souza, Ronald Buss
• Other Authors: National Research Foundation, Swedish Foundation for International Cooperation in Research and Higher Education, H2020 European Research Council, Knut och Alice Wallenbergs Stiftelse, Vetenskapsrådet, H2020 Marie Skłodowska-Curie Actions
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 2023
• Subjects: Southern Ocean
• Online Access: http://dx.doi.org/10.1098/rsta.2022.0058; https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2022.0058; https://royalsocietypublishing.org/doi/full-xml/10.1098/rsta.2022.0058

Interactions between the upper ocean and air-ice-ocean fluxes in the Southern Ocean play a critical role in global climate by impacting the overturning circulation and oceanic heat and carbon uptake. Remote and challenging conditions have led to sparse observational coverage, while ongoing field programmes often fail to collect sufficient information in the right place or at the time-space scales required to constrain the variability occurring in the coupled ocean-atmosphere system. Only within the last 10 years have we been able to directly observe and assess the role of the fine-scale ocean and rapidly evolving atmospheric marine boundary layer on the upper limb of the Southern Ocean's overturning circulation. This review summarizes advances in mechanistic understanding, arising in part from observational programmes using autonomous platforms, of the fine-scale processes (1–100 km, hours-seasons) influencing the Southern Ocean mixed layer and its variability. We also review progress in observing the ocean interior connections and the coupled interactions between the ocean, atmosphere and cryosphere that moderate air-sea fluxes of heat and carbon. Most examples provided are for the ice-free Southern Ocean, while major challenges remain for observing the ice-covered ocean. We attempt to elucidate contemporary research gaps and ongoing/future efforts needed to address them. 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'.