南海北部甲烷渗漏活动存在的证据:近底层海水甲烷高浓度异常

用吹扫-捕集法对东沙群岛西南和西沙海槽附近海域5个站位水柱中的甲烷浓度进行了测定,在其中的3个站位发现了甲烷高浓度异常。在东沙群岛西南海域的E105A和E106两站位近底层海水中甲烷浓度均出现异常增加,其值分别为4.25和10.64 nmol/dm3。在西沙海槽附近的E413站位甲烷异常出现在1 750,1 900和2 050 m深的近底层水中,浓度分别达5.17,8.48和8.70 nmol/dm3。在近底层海水中出现的甲烷高浓度异常是由于沉积物下部甲烷渗漏活动造成的,结合前人在这两个海域沉积物的地球物理和化学调查资料,认为可能是与冷泉渗漏或天然气水合物分解有关。2007年5月在探测到甲烷高浓度明显异常的东沙群岛西南神弧海域,获得了天然气水合物的实物样品,但是西沙海槽附近海域近底层水的甲烷高浓度异常是来源于天然气水合物还是来源于冷泉需要进一步加以确认。

The evidence for the existence of methane seepages in the northern South China Sea:abnormal high methane concentration in bottom waters

The methane concentration of water samples at five stations collected by the CTD rosette water sampler in the area of southwestern Dongsha Islands and the Xisha Trough,respectively,was analyzed by the gas-stripping method on aboard ship.It shows abnormal high methane concentrations in near bottom water samples at three stations.In the southwestern Dongsha Islands area,the methane concentrations of 4.25 and 10.64 nmol/dm3 occur in near bottom water samples at Stas E105A and E106,respectively.In the Xisha Trough area,the high methane concentrations of 5.17,8.48 and 8.70 nmol/dm3 in water depths of 1 750,1 900 and 2 050 m,respectively,have been observed at Sta E413.It is believed that the abnormal high methane concentrations are generated from the leakage of methane from sediments.Combining with previous geophysical and geochemical data from these two areas,this was probably related to the submarine gas hydrate decomposition and cold seep system.In May 2007,gas hydrate samples were successfully obtained by the drilling in Shenhu sea area located in the southwestern Dongsha Islands area.It is called for further drilling surveys to confirm the existence of gas hydrate and cold seep system in the Xisha Trough as early as possible.