Circumpolar distributions of age and anthropogenic CO2 content of Antarctic Bottom Water revealed by chlorofluorocarbon and sulfur hexafluoride

Abstract

Antarctic Bottom Water (AABW) sequesters anthropogenic CO2 (Cant) over the long-term and impacts the global carbon cycle. In this study, data of chlorofluorocarbon and sulfur hexafluoride observed from 2005 to 2020 in the Southern Ocean (SO) were used to investigate the age and Cant content of AABW. In the coastal regions of the Cosmonaut, Cooperation, D’Urville, and Somov Seas and near the Pacific-Antarctic Ridge, the age of AABW was < 5 years, reflecting the spread of newly formed AABW. Higher Cant inventory in AABW was detected in the Atlantic Ocean sector of the SO such as the Weddell and Lazarev Seas (29–55 ± 19–39 mol m−2) and the Cosmonaut and Cooperation Seas (35 ± 14 mol m−2) than those in the other regions. The amount of Cant in AABW in this region (7 ± 1–2 PgC) was estimated to be 78 % of the total Cant in AABW of the SO, suggesting the Atlantic Ocean sector as a major player to Cant sequestration in the abyssal ocean. The high Cant inventory in the Cosmonaut and Cooperation Seas is attributed to the presence of new AABW. The high Cant inventory also corresponded to the thick layer and high formation rate of AABW. Similar to the Cosmonaut and Cooperation Seas, the high Cant inventory in the Weddell and Lazarev Seas reflects the thick layer and high formation rate of AABW. The total amount of Cant in AABW in the SO (9 ± 1–2 PgC that would be the upper limit) was roughly estimated to be 15 % of the total Cant in the whole water column in the SO. This study highlights that AABW formation, transport, and storage processes play important roles in the total Cant sequestration in the SO.