| Summary: | Owing to its cool temperatures and vigorous water mass formation, the strongly eddying Southern Ocean is a key region of ocean CO 2 uptake. In this study we assess the role of 1) wind stress and buoyancy forcing and 2) the representation of mesoscale eddies, in affecting the mean and temporal variations of the Southern Ocean carbon uptake in the past 60 years. We analyze global ocean biogeochemistry simulations based on the NEMO-MOPS and FESOM-REcoM models and ranging from 1° and 0.5° resolutions (where eddies are parameterized) to eddy-rich 0.25° and 0.1° resolutions. The 0.25° model is also used to perform sensitivity experiments to unravel the relative role of wind stress and of buoyancy forcing for the carbon uptake variations. We find that eddy-rich models have steeper isopycnals across the Antarctic Circumpolar Current, which results in higher anthropogenic carbon uptake and storage than in models where eddies are parameterized. This, in combination with a somewhat lower outgassing of natural CO 2 , gives rise to a steeper trend of the Southern Ocean carbon uptake in the eddy-rich than in the eddy-parameterized models. Wind stress and buoyancy forcing are the main drivers of an increased outgassing of natural CO 2 over the past decades and drive most of its interannual and decadal variability, with wind stress dominating at subpolar latitudes, and buoyancy forcing in water mass formation regions. However, our experiments indicate that the stalling of the Southern Ocean carbon uptake in the 1990s was mostly driven by a reduction of its anthropogenic carbon uptake.
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