The submarine groundwater discharge as a carbon source to the Baltic Sea

Submarine Groundwater Discharge (SGD) is an important, yet poorly recognized pathway of material transport to the marine environment. This work reports on the results of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations in the groundwater seeping to the Bay of Puck. The loads of carbon via SGD were quantified for the Baltic Sea sub-basins and the entire Baltic Sea. The annual averages of DIC and DOC concentrations in the groundwater were equal to 64.5 ± 10.0 mg C L 1 and 5.8 ± 0.9 mg C L 1. The DIC and DOC fluxes via SGD to the Baltic Sea were estimated at 283.6 ± 66.7 kt yr 1 and 25.5 ± 4.2 kt yr 1. The SGD derived carbon load to the Baltic Sea is an important component of carbon budget, which turns the status of the sea into firmly heterotrophic. The carbon load to the World Ocean, which was calculated basing on few reports on groundwater discharges and the measured carbon concentrations, amounts to- (142–155) × 103 kt yr 1 (DIC), and (13–14) × 103 kt yr 1 (DOC). The carbon flux via SGD amounts to some 25% of the riverine carbon load, and should be included into the World Ocean carbon budget.