Improved winter data coverage of the Southern Ocean CO2 sink from extrapolation of summertime observations

• Published in: Communications earth & environment Vol. 3; no. 1; pp. 265 - 9
• Main Authors: Mackay, Neill, Watson, Andrew J., Suntharalingam, Parvada, Chen, Zhaohui, Landschützer, Peter
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 01.12.2022; Nature Portfolio
• Subjects: Antarctic front; Anthropogenic factors; Boundary layers; Carbon dioxide; Human influences; Learning algorithms; Machine learning; Mapping; Neural networks; Ocean basins; Reconstruction; Summer; Temperature effects; Uncertainty; Winter; Southern Ocean
• ISSN: 2662-4435; 2662-4435
• DOI: 10.1038/s43247-022-00592-6

The Southern Ocean is an important sink of anthropogenic CO 2 , but it is among the least well-observed ocean basins, and consequentially substantial uncertainties in the CO 2 flux reconstruction exist. A recent attempt to address historically sparse wintertime sampling produced ‘pseudo’ wintertime observations of surface pCO 2 using subsurface summertime observations south of the Antarctic Polar Front. Here, we present an estimate of the Southern Ocean CO 2 sink that combines a machine learning-based mapping method with an updated set of pseudo observations that increases regional wintertime data coverage by 68% compared with the historical dataset. Our results confirm the suggestion that improved winter coverage has a modest impact on the reconstruction, slightly strengthening the uptake trend in the 2000s. After also adjusting for surface boundary layer temperature effects, we find a 2004-2018 mean sink of −0.16 ± 0.07 PgC yr −1 south of the Polar Front and −1.27 ± 0.23 PgC yr −1 south of 35°S, consistent with independent estimates from atmospheric data.