Post‐drilling changes in fluid discharge pattern, mineral deposition, and fluid chemistry in the Iheya North hydrothermal field, Okinawa Trough

[1] The Integrated Ocean Drilling Program (IODP) Expedition 331 investigated the Iheya North hydrothermal field in the Okinawa Trough. Several post-drilling underwater vehicle investigations were conducted over 2 years to identify post-drilling changes in fluid discharge pattern, mineral deposition, and fluid chemistry. Drilling-induced high-temperature hydrothermal fluid vents were identified at deep holes not only near the naturally occurring NBC hydrothermal fluid vent (Site C0016) but also at the seafloor ∼450 m distal to the NBC vent (Site C0014), where no hydrothermal fluid discharge was observed prior to drilling. A chimney structure at Hole C0016A grew rapidly at the NBC mound crest, where only small chimneys had been found before drilling. A drilling-induced diffuse hydrothermal flow region spread at Site C0014, and this area was newly colonized by the galatheid crab. From a fluid chemistry perspective, the post-drilling hydrothermal fluids were enriched in Cl relative to seawater, although this fluid chemistry was not observed during the 12 years prior to drilling. The Cl-enriched fluid reservoir underlying the subseafloor impermeable layers, observed by IODP Expedition 331, is likely source for the Cl-enriched fluids discharging from the post-drilling vents. The drilling-induced physical disturbance of subseafloor hydrogeological structures would release such fluids to the seafloor. In turn, the rapid chimney growth at the NBC mound crest may also be attributed to highly turbulent fluid flow with the enlarged artificial vent of Hole C0016A, which can contribute to the retention of the fluid-seawater mixture for a sufficiently long period to precipitate sulfide/sulfate minerals on the seafloor.

[1]  K. Takai,et al.  Cell-Specific Thioautotrophic Productivity of Epsilon-Proteobacterial Epibionts Associated with Shinkaia crosnieri , 2012, PloS one.

[2]  Ko-ichi Nakamura,et al.  Liquid CO2 venting on the seafloor: Yonaguni Knoll IV hydrothermal system, Okinawa Trough , 2006 .

[3]  N. Yoshida,et al.  Geochemical origin of hydrothermal fluid methane in sediment-associated fields and its relevance to the geographical distribution of whole hydrothermal circulation , 2013 .

[4]  Satoshi Nakagawa,et al.  Hydrothermal fluid geochemistry at the Iheya North field in the mid-Okinawa trough: Implication for origin of methane in subseafloor fluid circulation systems , 2011 .

[5]  B. Popp,et al.  Determination of Concentration and Carbon Isotopic Composition of Dissolved Methane in Sediments and Nearshore Waters , 1995 .

[6]  Tatsuo Aono,et al.  Dispersion of artificial caesium-134 and -137 in the western North Pacific one month after the Fukushima accident , 2012, GEOCHEMICAL JOURNAL.

[7]  Ken Takai,et al.  Geochemical and microbiological evidence for a hydrogen-based, hyperthermophilic subsurface lithoautotrophic microbial ecosystem (HyperSLiME) beneath an active deep-sea hydrothermal field , 2004, Extremophiles.

[8]  T. Umezawa,et al.  A High-precision Measurement System for Carbon and Hydrogen Isotopic Ratios of Atmospheric Methane and Its Application to Air Samples Collected in the Western Pacific Region , 2009 .

[9]  Miho Hirai,et al.  Microbial Diversity in Deep-sea Methane Seep Sediments Presented by SSU rRNA Gene Tag Sequencing , 2012, Microbes and environments.

[10]  Satoshi Tsukioka,et al.  Hydrothermal plumes imaged by high‐resolution side‐scan sonar on a cruising AUV, Urashima , 2010 .

[11]  Fabien Kenig,et al.  Fluids from Aging Ocean Crust That Support Microbial Life , 2003, Science.

[12]  A. Schultz,et al.  Temporal variations in diffuse hydrothermal flow at TAG , 1996 .

[13]  W. Goodfellow,et al.  Geochemistry of fluid phases and sediments: Relevance to hydrothermal circulation in Middle Valley, ODP Legs 139 and 169 , 2002 .

[14]  Y. Takano,et al.  Mineralogy and Isotope Geochemistry of Active Submarine Hydrothermal Field at Suiyo Seamount, Izu–Bonin Arc, West Pacific Ocean , 2008 .

[15]  K. V. Damm,et al.  Chemistry of submarine hydrothermal solutions at Guaymas Basin, Gulf of California , 1985 .

[16]  Fumiko Nakagawa,et al.  Development of a multibottle gas‐tight fluid sampler WHATS II for Japanese submersibles/ROVs , 2006 .

[17]  Y. Sako,et al.  Variability in microbial community and venting chemistry in a sediment-hosted backarc hydrothermal system: Impacts of subseafloor phase-separation. , 2005, FEMS microbiology ecology.

[18]  Ken Takai,et al.  Isotopic variation of molecular hydrogen in 20°-375°C hydrothermal fluids as detected by a new analytical method , 2010 .

[19]  Y. Nakaguchi,et al.  Dissolved selenium species in the Sulu Sea, the South China Sea and the Celebes Sea , 2004 .

[20]  Hydrothermal fluid flow system around the Iheya North Knoll in the mid-Okinawa trough based on seismic reflection data , 2012 .

[21]  Kentaro Nakamura,et al.  Iron-Based Microbial Ecosystem on and Below the Seafloor: A Case Study of Hydrothermal Fields of the Southern Mariana Trough , 2012, Front. Microbio..

[22]  U. Tsunogai,et al.  An analytical system for determining delta17O in CO2 using continuous flow-isotope ratio MS. , 2005, Analytical Chemistry.

[23]  Y. Kato,et al.  Major and trace element geochemistry and Os isotopic composition of metalliferous umbers from the Late Cretaceous Japanese accretionary complex , 2005 .