Decrease in air-sea CO₂ fluxes caused by persistent marine heatwaves

Regional processes play a key role in the global carbon budget. Major ocean CO₂ uptake at mid-latitudes counteracts CO₂ 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 CO₂ 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 CO₂ uptake and release areas. Average air-sea CO₂ flux density changes from persistent marine heatwaves are strongest in the Pacific Ocean with a 40 ± 9% reduction in CO₂ release in the tropics linked to ENSO, and a reduction in CO₂ 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.