Exchangeable dissolved organic carbon (EDOC) makes up a significant proportion (30–67%) of the oceanic dissolved organic carbon (DOC) pool, yet the sources of EDOC to the ocean are poorly constrained. We measured the exchange of EDOC and concentrations of EDOC and DOC over a 26º latitudinal gradient. A clear latitudinal trend was observed, with the highest EDOC concentrations in the tropics. EDOC exports to the coastal ocean were 4.7 ± 1.9 mmol m2 d-1, equivalent to 11% of DOC exports (42.1 ± 6.7 mmol m2 d-1). EDOC concentrations were equal to 13 ± 4% of DOC concentrations. Based on previous global DOC exports, and the EDOC:DOC ratios found here, mangroves may outwell 3.1 Tg C yr-1 as EDOC. This is equivalent to ~60% of the estimated global EDOC flux from the ocean to the atmosphere and ~2% of the modelled atmospheric EDOC deposition to the ocean.
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