| Summary: | 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.
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