Widespread seepage of methane from seafloor sediments on continental margins are released into seawater, a portion of which may escape to the atmosphere. To assess the water column distribution characteristics of methane and its input to the atmosphere, we investigated methane emissions from the shelf and west slope of the back-arc Okinawa Trough (OT), East China Sea. Our results showed a heterogeneity distribution of methane within the water column. The highest value, which was more than 10 times of the background concentration, occurred near a cold seep in the north of the study area which was discovered by a remotely operated underwater vehicle (ROV). Other sources of methane to the water column of the OT, besides cold seepage input, probably also include in situ aerobic methane production, advective transport from the continental shelf, and/or hydrothermal venting. Furthermore, the sea-to-air flux of methane throughout the study area was up to 116 μmol m^–2d^–1, noticeably higher than that in many other continental shelf waters and seep sites globally, indicating that this region is an active CH₄ emission area. Our findings demonstrate that methane discharged from both cold seeps and hydrothermal vents have a significant influence on the methane cycle in the OT, providing a new insight for the methane budget of back-arc basins.

大陆边缘海底沉积物中甲烷的广泛渗漏被释放到海水中，其中一部分可能逃逸到大气中。为了评估甲烷在水柱中的分布特征及其向大气中的输入，我们调查了东海后冲绳海槽（OT）的陆架和西坡的甲烷排放量。我们的结果表明水柱内甲烷的非均质性分布。最高值超过背景浓度的10倍，出现在研究区北部的一个冷渗漏附近，该渗漏是由遥控水下航行器（ROV）发现的。除冷渗流输入外，加湿器水柱中的其他甲烷来源可能还包括原位有氧甲烷生产，来自大陆架的平流运输和/或热液排放。此外，整个研究区域的甲烷海对空气通量高达116μmolm ^–2 d ^–1，明显高于全球许多其他大陆架水和渗漏点，表明该区域是活跃的CH _4个发射区。我们的发现表明，从冷渗漏孔和热液喷口排放的甲烷对OT中的甲烷循环有重大影响，这为后弧盆地的甲烷收支提供了新的见解。