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.