南海西沙西南海底广泛发育规模巨大的海底麻坑,麻坑内GC14柱样5.7 m到6.7 m深度孔隙水中Cl-浓度降低,同时伴随δ18O值升高,显示有天然气水合物的发育.同时,孔隙水中的Cl-,Na+和K+浓度主要沿着海水稀释线分布,排除了黏土矿物脱水引起Cl-浓度降低和δ18O值升高的可能性.根据Cl-浓度和δ18O值异常估算的水合物饱和度分别为6％～10％和7％～15％.由此可以推断,西沙西南麻坑区可能是具有良好水合物勘探前景的海域.%Mega-pockmarks are widely scattered throughout the southwestern Xisha Uplift,northern South China Sea (SCS).Pore water collected from a gravity-core inside of a mega-pockmark exhibited a decrease in the Cl-concentration concomitant with an increase in the δ18O value at the interval of 5.7～6.7 m below the seafloor,suggesting a possible gas hydrate occurrence.The Cl-,Na+,and K+ concentrations cluster mainly along the seawater freshening line without a distinct Na+ enrichment and K+ depletion.The gas hydrate contents were estimated to be between 6％～10％,and 7％～15％,respectively,according to the C1-concentration offsets and the δ18O values obtained from the baselines.The southwestern Xisha Uplift pockmark field is likely to be a good prospective area for the occurrence of gas hydrates in the shallow sediments.
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