Change of Gas Hydrate Reservoir and Its Effect on the Environment in Xisha Trough since the Last Glacial Maximum

Abstract

In this article, Milkov and Sassen's model is selected to calculate the thickness of the gas hydrate stable zone (GHSZ) and the amount of gas hydrate in the Xisha () Trough at present and at the last glacial maximum (LGM), respectively, and the effects of the changes in the bottom water temperature and the sea level on these were also discussed. The average thickness of the GHSZ in Xisha Trough is estimated to be 287 in and 299 m based on the relationship between the GHSZ thickness and the water depth established in this study at present and at LGM, respectively. Then, by assuming that the distributed area of gas hydrates is 8 000 km(2) and that the gas hydrate saturation is 1.2% of the sediment volume, the amounts of gas hydrate are estimated to be similar to 2.76x10(10) m(3) and similar to 2.87x10(10) m(3), and the volumes of hydrate-bound gases are similar to 4.52x10(12) m(3) and -4.71x10(12) m(3) at present and at LGM, respectively. The above results show that the thickness of GHSZ decreases with the bottom water temperature increase and increases with the sea level increase, wherein the effect of the former is larger than that of the latter, that the average thickness of GHSZ in Xisha Trough had been reduced by similar to 12 m, and that 1.9X10(11) m(3) of methane is released from approximately 1.1x10(9) m(3) of gas hydrate since LGM. The released methane should have greatly affected the environment.