Abstract
Since the initial discovery of hydrothermal vents in 1977, these ‘extreme’ chemosynthetic systems have been a focus of interdisciplinary research. The Okinawa Trough (OT), located in the semi-enclosed East China Sea between the Eurasian continent and the Ryukyu arc, hosts more than 20 known vent sites but all within a relatively narrow depth range (600–1880 m). Depth is a significant factor in determining fluid temperature and chemistry, as well as biological composition. However, due to the narrow depth range of known sites, the actual influence of depth here has been poorly resolved. Here, the Yokosuka site (2190 m), the first OT vent exceeding 2000 m depth is reported. A highly active hydrothermal vent site centred around four active vent chimneys reaching 364°C in temperature, it is the hottest in the OT. Notable Cl depletion (130 mM) and both high H2 and CH4 concentrations (approx. 10 mM) probably result from subcritical phase separation and thermal decomposition of sedimentary organic matter. Microbiota and fauna were generally similar to other sites in the OT, although with some different characteristics. In terms of microbiota, the H2-rich vent fluids in Neuschwanstein chimney resulted in the dominance of hydrogenotrophic chemolithoautotrophs such as Thioreductor and Desulfobacterium. For fauna, the dominance of the deep-sea mussel Bathymodiolus aduloides is surprising given other nearby vent sites are usually dominated by B. platifrons and/or B. japonicus, and a sponge field in the periphery dominated by Poecilosclerida is unusual for OT vents. Our insights from the Yokosuka site implies that although the distribution of animal species may be linked to depth, the constraint is perhaps not water pressure and resulting chemical properties of the vent fluid but instead physical properties of the surrounding seawater. The potential significance of these preliminary results and prospect for future research on this unique site are discussed.
Highlights
The discovery of deep-sea hydrothermal vent [1,2] brought to light various unique processes occurring under the vast seawater mass
The dominance of the deep-sea mussel Bathymodiolus aduloides is surprising given other nearby vent sites are usually dominated by B. platifrons and/or B. japonicus, and a sponge field in the periphery dominated by Poecilosclerida is unusual for Okinawa Trough (OT) vents
During Remotely Operated Vehicle (ROV) KAIKO dive no. 668, the southern slope of the southern minor ridge was surveyed for hydrothermal signatures such as increases in water column turbidity and benthic animal density, but none was detected
Summary
The discovery of deep-sea hydrothermal vent [1,2] brought to light various unique processes occurring under the vast seawater mass. Four decades of cruise observations, in addition to theoretical and experimental approaches, led to the accumulation of a large dataset and knowledge with regards to global distribution of vent sites [3,4], heat and elemental flux between solid earth and ocean [5,6] including sulfide ore generation [7,8], physiological and phylogenetic characteristics of (hyper)thermophilic chemolithotrophic microbes [9,10] and vent-endemic fauna [11,12], as well as biogeography [13] Based on this knowledge and from the primal perspective of energetics that bridges them [14], a generalized model predicting the relationships between underlying geology, fluid chemistry and microbial chemosynthetic primary production [15], applicable to presume habitability of ancient Earth [16,17] and extraterrestrial bodies [18,19], has been built. The ECS opens to the Pacific Ocean only via several straits shallower than 1100 m while its internal basin in the south, the southern
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