AUTHOR=Silvano Alessandro , Purkey Sarah , Gordon Arnold L. , Castagno Pasquale , Stewart Andrew L. , Rintoul Stephen R. , Foppert Annie , Gunn Kathryn L. , Herraiz-Borreguero Laura , Aoki Shigeru , Nakayama Yoshihiro , Naveira Garabato Alberto C. , Spingys Carl , Akhoudas Camille Hayatte , Sallée Jean-Baptiste , de Lavergne Casimir , Abrahamsen E. Povl , Meijers Andrew J. S. , Meredith Michael P. , Zhou Shenjie , Tamura Takeshi , Yamazaki Kaihe , Ohshima Kay I. , Falco Pierpaolo , Budillon Giorgio , Hattermann Tore , Janout Markus A. , Llanillo Pedro , Bowen Melissa M. , Darelius Elin , Østerhus Svein , Nicholls Keith W. , Stevens Craig , Fernandez Denise , Cimoli Laura , Jacobs Stanley S. , Morrison Adele K. , Hogg Andrew McC. , Haumann F. Alexander , Mashayek Ali , Wang Zhaomin , Kerr Rodrigo , Williams Guy D. , Lee Won Sang TITLE=Observing Antarctic Bottom Water in the Southern Ocean JOURNAL=Frontiers in Marine Science VOLUME=10 YEAR=2023 URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1221701 DOI=10.3389/fmars.2023.1221701 ISSN=2296-7745 ABSTRACT=

Dense, cold waters formed on Antarctic continental shelves descend along the Antarctic continental margin, where they mix with other Southern Ocean waters to form Antarctic Bottom Water (AABW). AABW then spreads into the deepest parts of all major ocean basins, isolating heat and carbon from the atmosphere for centuries. Despite AABW’s key role in regulating Earth’s climate on long time scales and in recording Southern Ocean conditions, AABW remains poorly observed. This lack of observational data is mostly due to two factors. First, AABW originates on the Antarctic continental shelf and slope where in situ measurements are limited and ocean observations by satellites are hampered by persistent sea ice cover and long periods of darkness in winter. Second, north of the Antarctic continental slope, AABW is found below approximately 2 km depth, where in situ observations are also scarce and satellites cannot provide direct measurements. Here, we review progress made during the past decades in observing AABW. We describe 1) long-term monitoring obtained by moorings, by ship-based surveys, and beneath ice shelves through bore holes; 2) the recent development of autonomous observing tools in coastal Antarctic and deep ocean systems; and 3) alternative approaches including data assimilation models and satellite-derived proxies. The variety of approaches is beginning to transform our understanding of AABW, including its formation processes, temporal variability, and contribution to the lower limb of the global ocean meridional overturning circulation. In particular, these observations highlight the key role played by winds, sea ice, and the Antarctic Ice Sheet in AABW-related processes. We conclude by discussing future avenues for observing and understanding AABW, impressing the need for a sustained and coordinated observing system.