Abstract
AbstractLateral fluxes (i.e., outwelling) of dissolved organic (DOC) and inorganic (DIC) carbon and total alkalinity were estimated using radium isotopes at the groundwater, mangrove creek, and continental shelf scales in the Amazon region. Observations of salinity and radium isotopes in the creek indicated tidally driven groundwater exchange as the main source of carbon. Radium‐derived transport rates indicate that mangrove carbon is exported out of the continental shelf on timescales of 22 ± 7 d. Bicarbonate was the main form (82% ± 11%) of total dissolved carbon in all samples, followed by DOC (13% ± 12%) and CO2 (5% ± 4%). DIC (18.7 ± 15.7 mmol m−2 d−1) exceeded DOC (3.0 ± 4.1 mmol m−2 d−1) outwelling at all spatial scales. The interpretation of outwelling across the mangrove‐ocean continuum is related to the spatial and temporal scales investigated. At all scales, outwelling represented a major coastal carbon pathway driving bicarbonate storage in the ocean.
Highlights
Groundwater had the highest concentrations of radium isotopes, carbon, and total alkalinity (TA)
Radium isotopes Carbon outwelling in mangroves is triggered by the exchange of intertidal groundwater enriched in carbon through crab burrows (Taillardat et al 2018; Taniguchi et al 2019)
The daily variability of depth, salinity, and radium isotopes (Fig. 2) indicates that groundwater exchange in the mangrove creek is driven by tidal pumping
Summary
Outwelling estimates at the shelf scale integrate carbon fluxes from multiple sources including rivers and mangroves (Dittmar et al 2006). We compare total alkalinity (TA), dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC) outwelling at multiple scales (groundwater, mangrove creek, and continental shelf), and discuss if outwelling can drive long-term carbon sequestration in the ocean.
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