Alex Mignot, Karina Von Schuckmann, Florent Gasparin, Simon van Gennip, Peter Landschützer, Coralie Perruche, Julien Lamouroux, Tristan Amm

Regional processes play a key role in the global carbon budget. Major ocean carbon uptake at mid-latitudes counteracts carbon release in the tropics, which is modulated by episodes of marine heatwaves (MHWs). Yet, we lack essential knowledge on persistent MHWs (PMHWs), and their effect on the carbon sensitive areas. Here, based on a 1985-2017 joint analysis of reconstructions, ocean reanalysis, in situ and satellite data, we show that PMHWs occur in major carbon uptake and release areas. Air-sea CO2 flux changes from PMHWs are strongest in the Pacific Ocean with a 35 +/- 2 % reduction in CO2 release in the tropics linked to ENSO, and a reduction in CO2 uptake of 28 +/- 9 % in the North Pacific. 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.