A detectable change in the air-sea CO₂ flux estimate from sailboat measurements

The sailboat Seaexplorer collected underway sea surface partial pressure of CO₂ (pCO₂) data for 129 days (2018-2021), including an Antarctic circumnavigation. By comparing ensembles of data-driven air-sea CO₂ fluxes computed with and without sailboat data and applying a detection algorithm, we show that these sailboat observations significantly increase the regional carbon uptake in the North Atlantic and decrease it in the Southern Ocean. While compensating changes in both basins limit the global effect, the Southern Ocean-particularly frontal regions (40°S-60°S) during summertime-exhibited the largest air-sea CO₂ flux changes, averaging 20% of the regional mean. Assessing the sensitivity of the air-sea CO₂ flux to measurement uncertainty, the results stay robust within the expected random measurement uncertainty (± 5 μatm) but remain undetectable with a measurement offset of 5 µatm. We thus conclude that sailboats fill essential measurement gaps in remote ocean regions.