Hydrothermal systems are ubiquitous in various tectonic settings and are important in transferring internal mass and energy sources from the crust and mantle to the oceans. However, the biogeochemical processes involved in subseafloor hydrothermal circulation are not fully understood. This study investigated the compositional and isotopic properties of the high-temperature fluids collected from three hydrothermal vents of the Izena Hole in the middle Okinawa Trough in 2016 with Remotely Operated Vehicle (ROV) named Faxian. The results confirm that the latest geochemical parameters of the high-temperature hydrothermal fluids are similar to the previously reported parameters and indicate the origin of methane in the hydrothermal fluid. The nearly identical geochemistry of the three fluids indicate that they likely shared a common fluid reservoir. The endmember hydrothermal fluid contained isotopically ¹³C-moderate methane (− 30.4‰ to − 32.1‰), suggesting the predominance of thermogenic methane over biogenic methane incorporation in the hydrothermal fluids. The differences in the concentrations of ethane (C₁/C₂₊ = 11,600, 5600, 970 for Faxian-1, Faxian-2, and Faxian-3, respectively) and molecular hydrogen (0.11, 0.67, and 2.4 mM for Faxian-1, Faxian-2, and Faxian-3, respectively) suggest significantly different thermal fluid-sediment interaction during the discharge stage between two hydrothermal fields. The relatively low contents of biogenic methane in all the fluids here indicated limited biogenic methane incorporation during the recharge stage due to the horizontal restriction of hydrothermal fluid circulation. The geochemical origins of methane in hydrothermal fluid and their relevance to hydrothermal fluid circulation revealed herein shed light on the different degrees of sediment influence in various geological/geographical settings in the Okinawa Trough.

热液系统在各种构造环境中无处不在，在将内部质量和能源从地壳和地幔转移到海洋方面很重要。然而，海底热液循环所涉及的生物地球化学过程尚不完全清楚。本研究于 2016 年使用名为Faxian 的遥控飞行器 (ROV) 从冲绳海槽中部 Izena Hole 的三个热液喷口收集的高温流体的成分和同位素性质进行了研究。. 结果证实，高温热液流体的最新地球化学参数与先前报道的参数相似，表明了热液流体中甲烷的来源。这三种流体几乎相同的地球化学表明它们可能共享一个共同的流体储层。端元热液流体含有同位素¹³ C-中度甲烷（- 30.4‰至- 32.1‰），表明热液中产热甲烷的优势超过生物甲烷的掺入。乙烷浓度的差异（C ₁ /C ₂₊= 11,600、5600、970 分别为 Faxian-1、Faxian-2 和 Faxian-3）和分子氢（分别为 Faxian-1、Faxian-2 和 Faxian-3 的 0.11、0.67 和 2.4 mM）建议在两个热液场之间的排放阶段，热流体-沉积物相互作用显着不同。这里所有流体中生物甲烷含量相对较低，表明由于热液流体循环的水平限制，在补给阶段生物甲烷掺入有限。热液中甲烷的地球化学起源及其与热液循环的相关性揭示了冲绳海槽不同地质/地理环境中沉积物的不同程度影响。