Mangroves cover <0.03% of the Earth’s surface yet account for ~14% of oceanic carbon burial. Mangroves also export alkalinity to the coastal ocean, and act as sources/sinks of methane and nitrous oxide. The effect of these fluxes on climate may exceed carbon burial by several-fold, but are unaccounted for in blue carbon budgets. This proposal aims to constrain the magnitude and drivers of alkalinity and greenhouse gas fluxes in mangroves. Innovatively this study will bridge the terrestrial-aquatic divide by coupling high resolution radionuclide geochronology of soil carbon cycling with autonomous measurements of aquatic exports and greenhouse gas fluxes. This study will provide the detailed data required to refine the blue carbon paradigm.