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

Abstract

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 Ra-226 and Ra-228 isotopes. On the basis of Ra-228 and Ra-226 mass-balance models, we estimated the advective flux of Ra-226 through SGD to be similar to 270 x 10(12) dpm yr(-1) in the Yellow Sea. Using this Ra-226 flux and the measured 226 Ra activity in coastal groundwater, the submarine discharge of groundwater (mostly brackish groundwater) was calculated to be at least 40% of the river-water input (similar to 2.3 x 10(11) m(3) 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 (similar to 23 x 109 mol yr(-1) 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. (c) 2005 Elsevier B.V. All rights reserved.