Decrease in air-sea CO fluxes caused by persistent marine heatwaves.

Regional processes play a key role in the global carbon budget. Major ocean CO uptake at mid-latitudes counteracts CO release in the tropics, which is modulated by episodes of marine heatwaves. Yet, we lack essential knowledge on persistent marine heatwaves, and their effect on the CO sensitive areas. Here we show, using a 1985-2017 joint analysis of reconstructions, ocean reanalysis and in situ and satellite data, that persistent marine heatwaves occur in major CO uptake and release areas. Average air-sea CO flux density changes from persistent marine heatwaves are strongest in the Pacific Ocean with a 40 ± 9% reduction in CO release in the tropics linked to ENSO, and a reduction in CO uptake of 29 ± 11% in the North Pacific over the study period. These results provide new insights into the interplay of extreme variability and a critical regulating ocean ecosystem service, and pave the way for future investigations on its evolution under climate change.