Variations of pore water sulfate gradients in sediments as indicator for underlying gas hydrate in Shenhu Area, the South China Sea

Abstract

Shenhu Area is one of the most promising areas for gas hydrate exploration in the northern South China Sea (SCS). Pore water sulfate gradient, sulfate-methane interface (SMI) depth, and sulfate flux were analyzed at 53 sites in this area. SO4 −2 gradient ranges between 0.33 and 4.43 mmol L−1 m−1. SMI depths are from 7.7 to 87.9 mbsf. Sulfate flux varies between 2.0 and 26.9 mmol m−2 yr−1, with a mean of 11.7 mmol m−2 yr−1. Correlation coefficient between SMI depth and methane flux for the 53 sites is −0.80, implying that methane flux regulates the rate of anaerobic methane oxidation (AMO), SMI depth, and sulfate flux. Twelve anomalous fields with high methane flux and steep sulfate gradients were recognized. Bottom simulating reflector (BSR) is distributed mainly in areas where SMI depth is less than 50 mbsf or places with sulfate flux larger than 3.5 mmol m−2 yr−1. It is suggested that the Baiyun Sag and the Southern Uplift are potential areas for gas hydrate exploration.