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

Regional processes play a key role in the global carbon budget. Major ocean CO 2 uptake at mid-latitudes counteracts CO 2 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 2 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 2 uptake and release areas. Average air-sea CO 2 flux density changes from persistent marine heatwaves are strongest in the Pacific Ocean with a 40 ± 9% reduction in CO 2 release in the tropics linked to ENSO, and a reduction in CO 2 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. Ocean CO 2 uptake at mid-latitudes counteracts CO 2 release in the tropics, but we know little about the effects of marine heatwaves that modulate this process. Here, the authors use joint analysis of satellite measurements, in situ observation, reconstructions derived from machine learning algorithms, numerical model of the global ocean, and find that areas where PMHWs most frequently occur coincide with the regions that are the most critical for the oceanic carbon cycle.