Sailing through the southern seas of air-sea CO2 flux uncertainty

The Southern Ocean is among the largest contemporary sinks of atmospheric carbon dioxide on our planet; however, remoteness, harsh weather and other circumstances have led to an undersampling of the ocean basin, compared with its northern hemispheric counterparts. While novel data interpolation methods can in part compensate for such data sparsity, recent studies raised awareness that we have hit a wall of unavoidable uncertainties in air-sea CO2 flux reconstructions. Here, we present results from autonomous observing campaigns using a novel platform to observe remote ocean regions: sailboats. Sailboats are at present a free of charge environmentally friendly platform that recurrently pass remote ocean regions during round-the-globe racing events. During the past 5 years, we collected >350 000 measurements of the sea surface partial pressure of CO2 (pCO(2)) around the globe including the Southern Ocean throughout an Antarctic circumnavigation during the Vendee Globe racing event. Our analysis demonstrates that the sailboat tracks pass regions where large uncertainty in the air-sea CO2 flux reconstruction prevails, with regional oversaturation or undersaturation of the sea surface pCO(2). Sailboat races provide an independent cross-calibration platform for autonomous measurement devices, such as Argo floats, ultimately strengthening the entire Southern Ocean observing system.This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.