Water column imaging with multibeam echo-sounding in the mid-Okinawa Trough: Implications for distribution of deep-sea hydrothermal vent sites and the cause of acoustic water column anomaly
Water column imaging with multibeam echo-sounding in the mid-Okinawa Trough: Implications for distribution of deep-sea hydrothermal vent sites and the cause of acoustic water column anomaly
复制标题
DOI：
10.2343/geochemj.2.0387
复制
发表时间：
2015-01-01
影响因子：
0.8
通讯作者：
Okino, Kyoko
中科院分区：
文献类型：
--
作者：
Nakamura, Kentaro;Kawagucci, Shinsuke;Okino, Kyoko
沉积在海底热液喷口中的多金属硫化物最近引起了人们的注意，因为它们是铜、锌、铅、铟、镓、锗、Au和银等贱金属、稀有金属和贵金属的潜在深海矿产资源。为今后开发这类深海矿物资源，开发有效的海底热液活动勘探方法是提供最有希望的领域清单的关键。然而，传统的勘探方法可能既费力又耗时，需要进一步开发更有效的海底热液喷口勘探方法。在过去十年中，使用多波束回声测深系统进行的水柱观测已成功地应用于海底热液喷口的勘探。2013年和2014年，我们在冲绳海槽中部使用MBES系统进行了广泛的水柱调查。在调查期间，我们发现了10个热液喷口地点，包括以前已知的地点，属于四个相对较大的热液喷口区，分别位于Izena Hole、Iheya North Knoll、Iheya Small Ridge和Izena Hole西北15公里处的一座海山。所有热液喷口点都是2-3个喷口点一组，属于一个热液区。声学水柱异常的形态特征（垂直上升至距海底1 000米左右，宽度无明显变化）表明，声学水柱异常不是热液喷口流体流动直接造成的。声学水柱异常的顶部的深度（类似于500米）对应的深度相当不错的CO2相变从液体/笼形水合物蒸汽。这表明，声学水柱异常归因于水团，包括致密的液态CO2液滴与笼形水合物结壳，这是最初来自海底热液流体排放。
Polymetallic sulfides deposited in seafloor hydrothermal vents have recently attracted attention as potential deep-sea mineral resources for base, rare, and precious metals such as Cu, Zn, Pb, In, Ga, Ge, Au, and Ag. For future exploitation of this type of deep-sea mineral resources, development of effective methods for exploring seafloor hydrothermal activity is a key to provide the most promising list of fields. However, conventional exploration methods are likely laborious and time-consuming, and a more efficient methods for exploration of seafloor hydrothermal vents are to be further developed. In the last decade, water column observation using multibeam echo souder (MBES) systems have become successfully applied to exploration of seafloor hydrothermal vents. In 2013 and 2014, we conducted extensive water column surveys using MBES systems in the mid-Okinawa Trough. During the surveys, we detected 10 hydrothermal vent sites, including previously known sites, belonging to four relatively large hydrothermal vent fields, located at the Izena Hole, Iheya North Knoll, Iheya Small Ridge, and a seamount 15 km northwest of the Izena Hole. All of the hydrothermal vent sites are in groups of 2-3 vent sites belonging to a hydrothermal field. Morphological features of the acoustic water column anomalies (rising vertically up to similar to 1000 m from the seafloor without a significant change of width) implied that the acoustic water column anomalies were not caused directly by hydrothermal vent fluid flows. The depth of the top of the acoustic water column anomalies (similar to 500 m) corresponded rather well to the depth of the CO2 phase transition from liquid/clathratehydrate to vapor. This suggests that the acoustic water column anomalies are attributed to water mass including dense liquid CO2 droplets with clathrate-hydrate crusts, which are originally derived from the seafloor hydrothermal fluid discharges.