Up in the air Understanding ocean-atmospheric carbon dioxide (CO ₂ ) fluxes in the Southern Ocean is necessary for quantifying the global CO ₂ budget, but measurements in the harsh conditions there make collecting good data difficult, so a quantitative picture still is out of reach. Long et al . present measurements of atmospheric CO ₂ concentrations made by aircraft and show that the annual net flux of carbon into the ocean south of 45°S is large, with stronger summertime uptake and less wintertime outgassing than other recent observations have indicated. —HJS