Submarine groundwater discharge (SGD) into the Yellow Sea revealed by ²²⁸Ra and ²²⁶Ra isotopes: Implications for global silicate fluxes

We estimated the magnitude of submarine groundwater discharge (SGD) into the Yellow Sea, which is one of the largest continental shelves in the world, using ²²⁶Ra and ²²⁸Ra isotopes. On the basis of ²²⁸Ra and ²²⁶Ra mass-balance models, we estimated the advective flux of ²²⁶Ra through SGD to be ∼270 × 10¹² dpm yr^-1 in the Yellow Sea. Using this ²²⁶Ra flux and the measured ²²⁶Ra activity in coastal groundwater, the submarine discharge of groundwater (mostly brackish groundwater) was calculated to be at least 40% of the river-water input (∼2.3 × 10¹¹ m³ yr^-1). Then, on the basis of the SGD and the concentration of Si in coastal groundwater, we estimated the flux of Si through SGD to be 20-100% of that associated with river discharge (∼23 × 10⁹ mol yr^-1). This large SGD is likely to be due to the high tidal range (up to 10 m) and the wide distribution of sandy sediments in the Yellow Sea, favorable for the recirculation of seawater through bottom sediments and rocks. This result from such a large area implies that the Si flux through SGD may be significant on a global scale.