Resumen
Mangroves are carbon-rich ecosystems that store large quantities of carbon, mostly in soils. Early carbon (C) budgets indicated that >50% of mangrove C fixation was unaccounted for. This ?missing C? has now been discovered to be a large release (423 Tg C a-1) of porewater dissolved DIC (dissolved inorganic carbon), dissolved organic carbon (DOC), and total alkalinity (17 TMOL a-1) via lateral export derived from bacterial decomposition of soil organic matter. This large export originates from DIC produced over at least a 1.0?1.5 m soil profile (280?420 Tg C a-1) via decomposition of autochthonous and allochthonous inputs and/or likely mineralization in deep (=1 m) ancient soils. DOC and DIC export from mangroves equate to 41% and ?100% of export from the world?s tropical rivers, respectively. A newly revised blue carbon budget for the world?s mangroves indicates a mean ecosystem gross primary production (GPPE) to ecosystem respiration (RE) ratio of 1.35 and a net ecosystem production (NEP) of 794 g C m-2 a-1 (= global NEP of 117 Tg C a-1), reflecting net autotrophy. CORG burial is 5% and 9% of GPPE and NEPE, respectively. Mean RE/GPPE is 0.74 and carbon use efficiency averages 0.57, higher than for tropical humid forests (0.35).