Observing Antarctic Bottom Water in the Southern Ocean

• Published in: Frontiers in Marine Science
• Main Authors: Alessandro Silvano, Sarah Purkey, Arnold L. Gordon, Pasquale Castagno, Andrew L. Stewart, Stephen R. Rintoul, Annie Foppert, Kathryn L. Gunn, Laura Herraiz-Borreguero, Shigeru Aoki, Yoshihiro Nakayama, Alberto C. Naveira Garabato, Carl Spingys, Camille Hayatte Akhoudas, Jean-Baptiste Sallée, Casimir de Lavergne, E. Povl Abrahamsen, Andrew J. S. Meijers, Michael P. Meredith, Shenjie Zhou, Takeshi Tamura, Kaihe Yamazaki, Kay I. Ohshima, Pierpaolo Falco, Giorgio Budillon, Tore Hattermann, Markus A. Janout, Pedro Llanillo, Melissa M. Bowen, Elin Darelius, Svein Østerhus, Keith W. Nicholls, Craig Stevens, Denise Fernandez, Laura Cimoli, Stanley S. Jacobs, Adele K. Morrison, Andrew McC. Hogg, F. Alexander Haumann, Ali Mashayek, Zhaomin Wang, Rodrigo Kerr, Guy D. Williams, Won Sang Lee
• Format: Article in Journal/Newspaper
• Language: English
• Published: Frontiers Media S.A. 2023
• Subjects: Antarctic Bottom Water (AABW); Southern Ocean; ice shelves; ocean warming; ocean freshening; Antarctic sea ice; Science; Q; General. Including nature conservation; geographical distribution; QH1-199.5; Antarctic; The Antarctic; Antarc*; Ice Sheet; Ice Shelves; Sea ice
• Online Access: https://doi.org/10.3389/fmars.2023.1221701; https://doaj.org/article/7ec8799498c04806b82197b2a7faab09

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.