CO2 outgassing south of 50°S  underestimated by up to 40% in previous studies

Southern Ocean surrounds Antarctica [image credit: theozonehole.com]

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‘Substantially underestimated winter CO2 sources of the Southern Ocean’ – is the title of this study at Science Advances. Researchers note that ‘previous observational gaps significantly bias’ understanding of the carbon cycle in this region, with ‘profound consequences’ of rectifying this. They conclude that: ‘By underestimating winter outgassing, previous analyses have not only miscalculated the net annual sink but also obscured the true seasonal dynamics. This introduces systematic errors into Earth system models.’ The IPCC is directly impacted by this, they say.
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From the abstract: ‘The size and control mechanism of the Southern Ocean’s carbon fluxes remain highly uncertain due to sparse winter observations. Here, we integrate satellite light detection and ranging (LIDAR) measurements with machine learning to assess the Southern Ocean air-sea CO2 fluxes between 2007 and 2020. We reveal that CO2 outgassing south of 50°S was underestimated by up to 40% in previous studies.’

‘While the midlatitude Southern Ocean (30° to 50°S) strengthens as a carbon sink, the high-latitude region (50° to 90°S) shows Southern Annular Mode (SAM)–modulated alternation between uptake and outgassing.[…] The findings underscore the winter processes’ critical role and necessitate year-round observations to understand Southern Ocean’s global carbon cycle impact.’
. . .
Further on in the study:
‘In conclusion, while the Southern Ocean CO2 sink has intensified over the past 14 years, our analysis, which integrates LIDAR’s unique winter observational capability, reveals contrasting seasonal mechanisms across latitudes and demonstrates that accurately capturing the magnitude of winter CO2 outgassing is essential. The ~40% underestimation of this high-latitude winter source due to previous observational gaps significantly biases our understanding of the high-latitude region’s carbon dynamics and its overall role in the global carbon budget.’
. . .
As a parting shot:
‘The consequences of rectifying the winter observational gap are profound. A weaker or more variable Southern Ocean carbon sink directly affects the global carbon budget assessments maintained by bodies like the Intergovernmental Panel on Climate Change (IPCC), potentially requiring adjustments to climate projections and national emission targets. By underestimating winter outgassing, previous analyses have not only miscalculated the net annual sink but also obscured the true seasonal dynamics. This introduces systematic errors into Earth system models, which rely on observational data for calibration and validation, thereby compromising their ability to accurately project future carbon-climate feedbacks.’

Full article here.