Toshitaka Gamo

Geochemical and microbiological evidence for a hydrogen-based, hyperthermophilic subsurface lithoautotrophic microbial ecosystem (HyperSLiME) beneath an active deep-sea hydrothermal field

Subsurface microbial communities supported by geologically and abiologically derived hydrogen and carbon dioxide from the Earth’s interior are of great interest, not only with regard to the nature of primitive life on Earth, but as potential analogs for extraterrestrial life. Here, for the first time, we present geochemical and microbiological evidence pointing to the existence of hyperthermophilic subsurface lithoautotrophic microbial ecosystem (HyperSLiME) dominated by hyperthermophilic methanogens beneath an active deep-sea hydrothermal field in the Central Indian Ridge. Geochemical and isotopic analyses of gaseous components in the hydrothermal fluids revealed heterogeneity of both concentration and carbon isotopic compositions of methane between the main hydrothermal vent (0.08xa0mM and −13.8‰ PDB, respectively) and the adjacent divergent vent site (0.2xa0mM and −18.5‰ PDB, respectively), representing potential subsurface microbial methanogenesis, at least in the divergent vent emitting more 13C-depleted methane. Extremely high abundance of magmatic energy sources such as hydrogen (2.5xa0mM) in the fluids also encourages a hydrogen-based, lithoautotrophic microbial activity. Both cultivation and cultivation-independent molecular analyses suggested the predominance of Methanococcales members in the superheated hydrothermal emissions and chimney interiors along with the other major microbial components of Thermococcales members. These results imply that a HyperSLiME, consisting of methanogens and fermenters, occurs in this tectonically active subsurface zone, strongly supporting the existence of hydrogen-driven subsurface microbial communities.

Chemical characteristics of newly discovered black smoker fluids and associated hydrothermal plumes at the Rodriguez Triple Junction, Central Indian Ridge

Abstract The chemical characteristics of hydrothermal fluids in the Indian Ocean have been revealed for the first time. A hydrothermal field (called the Kairei field), including active black smoker chimneys, was discovered by ROV Kaiko dives at 25°19.17′S, 70°02.40′E (∼2450 m depth) on the southwestern flank of an off-axis knoll located ∼15 miles north of the Rodriguez Triple Junction, Central Indian Ridge, after detailed tow-yo surveys of the hydrothermal plume distribution. The temperature of the fluid expelled from the most active chimney was almost stable (359–360°C) throughout three successive days of fluid sampling. The endmember fluid has a chemical composition similar to the hydrothermal fluids sampled from sediment-starved mid-ocean ridges in the Pacific and the Atlantic oceans, suggesting typical interactions between hot fluid and mid-ocean ridge basalts in the subseafloor reaction zone.

First Hydrothermal Vent Communities from the Indian Ocean Discovered

Abstract Thriving chemosynthetic communities were located for the first time in the Indian Ocean between 2420 and 2450 m, on a volcanic knoll at the eastern crest of an axial valley, approximately 22 km north of the Rodriguez Triple Junction. The communities were distributed in a 40m by 80m field around the knoll. At least seven active vent sites, including black smoker complexes that were emitting superheated water at 360°C, were observed at the field. The faunal composition of the Indian Ocean hydrothermal vent communities had links to both Pacific and Atlantic vent assemblages. This discovery supports the hypothesis that there is significant communication between vent faunas in the Pacific and Atlantic Oceans via active ridges in the Indian Ocean.

Stable isotopic compositions and fractionations of carbon monoxide at coastal and open ocean stations in the Pacific

[1]xa0Included in this report are the results of the first isotopic studies of seawater-dissolved carbon monoxide (CO). Large variations in both carbon and oxygen isotopic compositions (δ13C: −44.7 ∼ −21.1‰PDB, and δ18O: +8.7 ∼ +32.9‰SMOW) were observed in seawater-dissolved CO due to the combination of isotopically light CO production in seawater and the enrichment of heavy isotopes during the microbial consumption of CO. Compared with the total δ13C value of dissolved organic matter (DOM), the isotopic compositions of the photochemically produced CO in seawater are depleted in 13C by more than 20‰, probably due to large fractionation processes during the photochemical production of CO from DOM. In addition, the isotopic fractionation factors resulting from the microbial oxidation of CO in seawater were estimated to be 1.005 ± 0.002 and 1.006 ± 0.002 for carbon (αc) and oxygen (αo) based on the incubation experiments. By calculating the weighted mean of the isotopic composition of CO according to the CO concentration observed in surface seawater, the mean δ13C and δ18O for CO emitted from the oceans were estimated to be −40‰ PDB and +15‰ SMOW, respectively. Oceanic CO is a unique source of 13C and 18O-depleted CO relative to that of fossil fuel combustion and biomass burning, which will help us create a better isotopic mass balance for both global and local CO budget.

Stable isotope evidence for a putative endosymbiont-based lithotrophic Bathymodiolus sp. mussel community atop a serpentine seamount

A putative endosymbiont-based benthic animal community composed of at least two kinds of bivalves has been found atop the South Chamorro serpentine seamount in the Mariana fore-arc, western Pacific. Multiple stable isotopic analyses (hydrogen, carbon, nitrogen, and sulfur) were carried out on the soft tissues of an undescribed mussel species belonging to the genus Bathymodiolus . Markedly higher stable carbon ( i 13 C: m 21.4 to m 18.9 vs. PDB) and lower sulfur ( i 34 S: +10.2 to +10.6 vs. CDT) isotopic compositions of the mussel tissues suggested that they utilized both methane and sulfide as nutrient sources of carbon and sulfur. Analyses of in situ shimmering water and clayey sediment under the mussel bed supported these findings. These results strongly suggest that the mussels harbored both methanotrophic and thioautotrophic bacterial symbionts in their gills. This is the first stable isotopic evidence of a dual symbiotic Bathymodiolus sp. in the western Pacific. It is proposed that the major substrates for energy acquisition--methane and hydrogen sulfide--may be responsible for results from serpentinization in the lower crust. This abiotic process would be followed by abiotic or archaeal methane production and bacterial sulfate-reduction as evidenced by high i 13 C value ( m 14.6) of methane in the shimmering water and low i 34 S value ( m 32.3) of sulfides in the immediate sediments, respectively. Due to the very low organic matter content (0.5 mg C/g dry sediment) of the immediate sediment, it is further proposed that sulfate-reduction occurred using hydrogen (or possibly methane) as an electron donor. Thus, the mussel community living independently of magmatism and sedimentary organic matter is a lithotrophic animal community.

9 - Submarine hydrothermal activity in coastal zones

This chapter discusses the submarine hydrothermal activity in coastal zones. Coastal hydrothermal acitivity is observed at several sites in the Mediterranean Sea and western Pacific and is almost always associated with arc volcanism at subduction zones. While deep-sea hydrothermal fluids are mainly derived from the circulation of seawater beneath the seafloor, coastal hydrothermal fluids are derived from a complex mixture of seawater, meteoric water (groundwater), and magmatic fluids. In addition, tidal forcing, sea level change, and earthquake activity may significantly affect the rates of fluid venting and dispersion of hydrothermal plumes. The chemical composition of coastal hydrothermal fluids is therefore variable because it depends not only on fluid–rock interaction at high temperatures but also on the rate of subduction of the slabmaterial at the convergent plate margin and the decomposition of organic matter within the coastal sediments through which the fluids pass.

In Situ Measurement of Dissolvable Mn in Bottom Seawater in Combination with a Deep-Sea Cable off Hatsushima Island, Western Sagami Bay, Japan

We report the first success of a long-term (81 days) measurement using an in situ flow-through chemical analyzer, which was connected with a submarine cable for power supply and real-time data acquisition. The experiment was conducted at a plate boundary site in Sagami Bay, south of Japan, where a cable-connected submarine observatory (Hatsushima Underwater Observatory) has been available for geophysical and ecological monitoring studies. This study demonstrates a new possibility of application of submarine cables for advancing geochemical researches.