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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., (© 2022. The Author(s).)

Ocean warming, acidification, deoxygenation and reduced productivity are widely considered to be the major stressors to ocean ecosystems induced by emissions of CO 2 . However, an overlooked stressor is the change in ocean circulation in response to climate change. Strong changes in the intensity and position of the western boundary currents have already been observed, and the consequences of such changes for ecosystems are beginning to emerge. In this study, we address climatically induced changes in ocean circulation on a global scale but relevant to propagule dispersal for species inhabiting global shelf ecosystems, using a high-resolution global ocean model run under the IPCC RCP 8.5 scenario. The ¼ degree model resolution allows improved regional realism of the ocean circulation beyond that of available CMIP5-class models. We use a Lagrangian approach forced by modelled ocean circulation to simulate the circulation pathways that disperse planktonic life stages. Based on trajectory backtracking, we identify present-day coastal retention, dominant flow and dispersal range for coastal regions at the global scale. Projecting into the future, we identify areas of the strongest projected circulation change and present regional examples with the most significant modifications in their dominant pathways. Climatically induced changes in ocean circulation should be considered as an additional stressor of marine ecosystems in a similar way to ocean warming or acidification., (© 2017 John Wiley & Sons Ltd.)