Inorganic carbon and alkalinity biogeochemistry and fluxes in an intertidal beach aquifer: Implications for ocean acidification
Abstract
While submarine groundwater discharge (SGD) is well known to release large amounts of dissolved nutrients and organic carbon into the ocean, the contribution of SGD to the marine inorganic carbon cycle remains poorly understood. Here, we investigate the biogeochemistry of inorganic carbon in an intertidal aquifer and related SGD-derived fluxes into Tolo Harbor, Hong Kong over tidal and seasonal time scales. The results reveal production of total alkalinity (TAlk) and dissolved inorganic carbon (DIC) in the intertidal aquifer over the entire salinity range. The produced TAlk and DIC in the intertidal aquifer contributes >50% of the SGD-derived TAlk and DIC fluxes to the ocean. The distribution of TAlk and DIC in the transition (mangrove) and high salinity (bare beach) zones were different due to the distinct hydrogeological and geochemical conditions. In the organic-rich mangrove zone, TAlk and DIC production was driven by aerobic respiration and sulfate reduction. In the organic-poor bare beach zone, TAlk and DIC production was driven by calcite dissolution and dolomite precipitation. pH, temperature, physical mixing, and iron cycling in the intertidal aquifer also significantly influenced the carbonate biogeochemistry. The TAlk inventory in the intertidal aquifer was stable but the SGD-derived TAlk flux was ~60% greater in the wet season (73.3 mol/d per m coastline) than in the dry season (45.6 mol/d per m coastline). The DIC inventory in the intertidal aquifer and SGD-derived fluxes were ~24% and 95% higher in the wet season than in the dry season. Overall, through comparing the TAlk:DIC ratios in the SGD flux and seawater, this study indicates that SGD reduced the CO2 buffering capacity of the receiving ocean, and may serve as a local driver of ocean acidification.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H53I1865L
- Keywords:
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- 1817 Extreme events;
- HYDROLOGY;
- 1830 Groundwater/surface water interaction;
- HYDROLOGY;
- 1890 Wetlands;
- HYDROLOGY;
- 4235 Estuarine processes;
- OCEANOGRAPHY: GENERAL