Carbon dioxide emissions from coastal waters and mangrove sediments in a microtidal bay under tropical monsoon climate (Martinique, Lesser Antilles)

We report seasonal data of carbonate chemistry, partial pressure of CO₂ and air-sea CO₂ fluxes in coastal waters of the bay of Fort-de-France, where tidal amplitude was 20 cm. Sampling included the open bay, two small river mouths, a mangrove margin, and a mangrove channel and creek. To achieve a more complete carbon budget of the bay, CO₂ sediment-air fluxes were also measured with static chambers inside the mangrove at low tide. All water masses and sediments were a net source of CO₂ to the atmosphere. Microtidal conditions apparently resulted in little enrichment of bay's waters with dissolved CO₂, except in channels and creeks within the mangrove itself, where high concentrations of alkalinity were also recorded. Monsoonal climate caused a more significant, but still modest, export of dissolved CO₂ from the mangrove to the bay of Fort-de-France during the wet season, preferentially through small river mouths. We observed a fivefold increase of CO₂ emissions during the wet season compared to the dry season, with 73 % of this seasonal increase attributed to the mouths of small rivers draining the mangrove channels networks. Our data highlight that, because of the very low tidal amplitude, carbon export and emissions from the mangrove mainly varied according to the monsoonal regime, increasing during the wet season.