Surface-water carbon exchange from mangroves and responses to global warming.

Mangroves are carbon-rich coastal ecosystems that contribute to climate change mitigation. However, a major component of their carbon budget - lateral export - remains poorly constrained. Here, we (1) quantify surface water lateral carbon exchange (SWLCE) from mangroves across local to global scales; (2) estimate its response to key environmental factors; and (3) forecast its changes under warming scenarios as defined by the Shared Socioeconomic Pathways (SSPs). The SWLCE from global mangroves averages at 101 mmol m-2 d-1 [95% confidence intervals: 72-284], dominated (62.6-93.6%) by dissolved inorganic carbon (DIC) export. Further, organic carbon degradation and carbonate dissolution dominate the processes generating DIC in estuarine and coastal mangroves. Under intermediate-to-high SSPs, SWLCE is projected to increase by up to 305%, reaching the plateau at temperature threshold of ~2.5 ⁰C warming, beyond which it declines. Our findings underscore that SWLCE results in significant carbon sequestration in coastal oceans, and therefore should be incorporated into mangrove carbon accounting.