The Global Contribution of Individual Submarine Groundwater Discharge Components to the Ocean

Abstract Saline submarine groundwater discharge (SSGD) contributes to ocean chemistry through water‐rock interactions as seawater circulates in coastal aquifers. Its components, driven by different mechanisms, exhibit varying residence times and degrees of chemical alteration, so constraining solute fluxes requires quantifying each component. We estimated global density‐driven and tidally driven SSGD and solute fluxes using numerical modeling and geospatial data. The modeled global fluxes of density‐driven circulation, nearshore tidal circulation, and tidal pumping are 23 (3–219) km 3 /yr, 254 (173–275) km 3 /yr, and 388 (179–1,032) km 3 /yr, respectively. Groundwater flow models often underestimate density‐driven circulation because aquifer heterogeneity creates complex salinity distributions that can increase fluxes by orders of magnitude. Accounting for heterogeneity and hydraulic conductivity uncertainty, the revised estimate for density‐driven circulation is 523 (181–1,705) km 3 /yr, comparable to the total tidal‐driven SGD. This water flux delivers ∼3 Tmol/yr Ca 2+ to the ocean, a significant fraction of the global riverine calcium input.