Mangrove ecosystems are our most carbon-rich forests. They play a vital role in regulating carbon fluxes to the ocean (outwelling). These ecosystems are increasingly threatened by degradation. Here we present a 5-year-long timeseries from 2014 to 2019 of dissolved organic and inorganic carbon outwelling from the Everglades National Park (Florida, US). The data includes a category 3-4 hurricane in 2017. Our results reveal a substantial and sustained decrease in both organic and inorganic carbon outwelling. Both remain low for up to two years following the hurricane. The mangrove estuarine contribution decreases compared to that of the marsh upstream. The proposed mechanisms are increased outwelling during the hurricane and extreme tree mortality, limiting root respiration. With more intense hurricanes in the future, carbon outwelling risks being permanently lowered, which could alter the buffering capacity of coastal ocean acidification depending on the ratio of carbon dioxide within dissolved inorganic carbon.
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