Improved air-sea CO₂ flux estimates from sailboat measurements

Despite their importance in the climate system, remote ocean regions and their ability to absorb anthropogenic carbon dioxide (CO₂) remain highly uncertain. To address this issue, citizen science initiatives, including sailboats, expand the observational network. Using observing system simulations and novel sailboat tracks, we demonstrate how integrating sailboat data improves estimates of ocean carbon uptake. While we underestimate the ocean carbon sink when mimicking real-world sampling, adding available sailboat data does not substantially improve reconstructions. Nevertheless, increased sampling reveals a stronger carbon sink, particularly between 40°S and 60°S. The improvement persists with hypothetical measurement uncertainties, but substantial differences arise depending on whether positive or negative biases are applied to the race track data. While we show that two additional circumnavigations already improve the ocean mean sink estimate, we further highlight the finding that the additional data remain insufficient to correct the overestimated CO₂ sink trend, calling for continuation of the ongoing data collection.