Deepest and hottest hydrothermal activity in the Okinawa Trough: the Yokosuka site at Yaeyama Knoll

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.

Population history of deep-sea vent and seepProvannasnails (Mollusca: Abyssochrysoidea) in the northwestern Pacific

“…subglabra was formed earlier than that for P. clathrata during the geological history of the Okinawa Trough. Provanna clathrata appears to have adapted to deeper depths and only occurs below 1400 m deep, whereas P. subglabra appears to occur throughout a wide depth range ( Table 1 ; also see Miyazaki et al, 2017 ). This agrees with the fact that depth of the back-arc basin spreading centre increases with time, meaning the deeper sites suitable for P. clathrata came into existence later than the shallower sites suitable for P. subglabra.…”

“…The northwestern Pacific is an excellent model system for examining such evolutionary processes, since there are back-arc vents (e.g., Okinawa Trough, Manus Basin) and hydrocarbon seeps (e.g., Sagami Bay, Nankai Trough) in close proximity. The Okinawa Trough is a back-arc basin with more than 10 known hydrothermal vent fields, and more continue to be discovered ( Ishibashi et al, 2015 ; Nakamura et al, 2015 ; Chen et al, 2017 ; Miyazaki et al, 2017 ). As these vents appeared only two million years ago at the southern end of the back-arc basin, the historical evidence of animals invading these habitats can still be recovered genetically, along with ongoing evolutionary and ecological processes.…”

Metagenomic Insights Into the Cycling of Dimethylsulfoniopropionate and Related Molecules in the Eastern China Marginal Seas

“…MeSH can be produced from the methylation of H 2 S (Drotar et al, 1987) or degradation of Met and S-methylcysteine (Bremner and Steele, 1978;Ferchichi et al, 1985;Taylor and Kiene, 1989). Okinawa Trough hydrothermal vents have been reported to be rich in H 2 S (Miyazaki et al, 2017a), additionally, Kawagucci et al (2013) found that H 2 S content reached 4.5 mM kg −1 in hydrothermal sediments in the northern Iheya. Therefore, we propose that much of the MeSH in the Okinawa hydrothermal field is likely to be produced from H 2 S methylation.…”

Distribution and Discharge of Dissolved Methane in the Middle Okinawa Trough, East China Sea

“…However, given that a variety of mud volcanoes, pockmarks, and cold seeps have been discovered in recent decades in the OT (Yin et al, 2003;Li et al, 2015;Sun et al, 2015;Xu et al, 2018), it is reasonable to infer that they may contribute a substantial amount of CH 4 to seawater. In addition, as a universal extreme system within the OT, modern hydrothermal activity is pervasive and vigorous from north to south, which can also discharge a large amount of CH 4 along with hydrothermal fluids (Sakai et al, 1990;Ishibashi et al, 1995Ishibashi et al, , 2014Inagaki et al, 2006;Miyazaki et al, 2017). Previous studies found that the distance between the site of the newly discovered cold seeps (Li et al, 2015;Xu et al, 2018) and the hydrothermal vents found in the past (Inagaki et al, 2006;Ishibashi et al, 2014) are less than several tens of kilometers apart.…”