Geochemical characteristics of carbon in core 973-4 from southwestern Taiwan Basin in northern South China Sea

对南海北部台西南盆地天然气水合物潜在区(973-4岩芯)碳的形态、含量和稳定同位素组成进行了分析,并探讨了成岩环境因素和细菌种群与碳地球化学行为的关系。结果显示:(1)TOC含量为0.4%~1.3%,δ~(13)CTOC为–26.7‰~–23.9‰,说明973-4岩芯主要为陆源有机质,能够满足微生物产甲烷的需要;DIC和δ~(13)CIC的垂向变异及其显著负相关,指示:973-4岩芯560~890 cm深度段有SO42–驱动的AOM反应。(2)p H、Eh、沉积物粒径等成岩环境参数与TOC、IC、δ~(13)CTOC、δ~(13)CIC等碳地化参数显著相关。(3)细菌种群与DIC、δ~(13)CIC显著相关。结论认为:(1)973-4岩芯碳的地化行为与天然气水合物成藏存在明显响应关系。(2)成岩环境参数的垂向变异与碳的地球化学特征密切相关。(3)细菌种群对碳的地化参数变异有着显著影响。In the study, we analyze the carbon forms and stable isotope compositions of sediments from core 973-4 in the southwestern Taiwan Basin in the northern South China Sea. We also discuss the effect of diagenetic environmental factors and bacterial communities on the geochemical characteristics of carbon. Our results show that most of the sedimentary organic matter was terrigenous in origin based on δ13CTOC values of –26.7‰ to –23.9‰. The TOC content ranged between 0.4 and 1.3 wt.%, which is sufficient to produce methane. The dissolved inorganic carbon(DIC) was significantly and negatively correlated with the δ13CIC, indicating that the anaerobic oxidation of methane(AOM) driven by SO42– occurred at depths of 560–890 cm in core 973-4. Hence, these carbon geochemical characteristics have obviously responded to the accumulation of gas hydrates. Based on our statistical analysis, variations in the diagenetic environmental factors are closely related to the carbon behaviors. The bacterial communities in the sediments of core 973-4 greatly affected the carbon transformation. These study results are consistent with the theory that gas hydrate formation and microbial communities indicate the presence of marine gas hydrates.国家自然科学基金项目资助(41276046)~