Katsumi Marumo

Hydrothermal plume particles and dissolved phosphate over the superfast-spreading southern East Pacific Rise

Abstract The distribution and elemental composition of hydrothermal plume particles were mapped along the superfast spreading southern East Pacific Rise from the Garret Transform Fault to ∼19°S. Hydrographic and optical data were obtained using a series of seven tow-yos and thirty vertical casts employing a rosette sampler with 19-L PVC bottles for collecting discrete samples of various dissolved and particulate hydrothermal species. The extent of hydrothermal plume coverage over the southern East Pacific Rise between 13°33′ and 18°40′S is significantly greater than in other ridgecrest systems. The region south of 17°20′S is characterized by significant enrichments of volatile gases resulting from magmatic input of fresh lava at the seafloor. Between 17°20′ and 18°40′S, the ratio of S Fe in the plume particles is highly correlated with the dissolved gases in the neutrally-buoyant hydrothermal plumes. Plume inventories of Fe and S over this portion of the southern East Pacific Rise are 6–150 times higher than what has been observed over other vent fields because the total abundance of plumes is much greater. In addition, significant depletions (> 100 nmol/L) of dissolved phosphate over the ridge axis were observed at the depth of the hydrothermal plumes. These results provide clear evidence that this section of the southern East Pacific Rise maintains the most extensive complex of hydrothermal plumes observed thus far on the global ridgecrest system.

Biogeography and biodiversity in sulfide structures of active and inactive vents at deep-sea hydrothermal fields of the Southern Mariana Trough.

ABSTRACT The abundance, diversity, activity, and composition of microbial communities in sulfide structures both of active and inactive vents were investigated by culture-independent methods. These sulfide structures were collected at four hydrothermal fields, both on- and off-axis of the back-arc spreading center of the Southern Mariana Trough. The microbial abundance and activity in the samples were determined by analyzing total organic content, enzymatic activity, and copy number of the 16S rRNA gene. To assess the diversity and composition of the microbial communities, 16S rRNA gene clone libraries including bacterial and archaeal phylotypes were constructed from the sulfide structures. Despite the differences in the geological settings among the sampling points, phylotypes related to the Epsilonproteobacteria and cultured hyperthermophilic archaea were abundant in the libraries from the samples of active vents. In contrast, the relative abundance of these phylotypes was extremely low in the libraries from the samples of inactive vents. These results suggest that the composition of microbial communities within sulfide structures dramatically changes depending on the degree of hydrothermal activity, which was supported by statistical analyses. Comparative analyses suggest that the abundance, activity and diversity of microbial communities within sulfide structures of inactive vents are likely to be comparable to or higher than those in active vent structures, even though the microbial community composition is different between these two types of vents. The microbial community compositions in the sulfide structures of inactive vents were similar to those in seafloor basaltic rocks rather than those in marine sediments or the sulfide structures of active vents, suggesting that the microbial community compositions on the seafloor may be constrained by the available energy sources. Our findings provide helpful information for understanding the biogeography, biodiversity and microbial ecosystems in marine environments.

Abundance of Zetaproteobacteria within crustal fluids in back-arc hydrothermal fields of the Southern Mariana Trough

To extend knowledge of subseafloor microbial communities within the oceanic crust, the abundance, diversity and composition of microbial communities in crustal fluids at back-arc hydrothermal fields of the Southern Mariana Trough (SMT) were investigated using culture-independent molecular techniques based on 16S rRNA gene sequences. Seafloor drilling was carried out at two hydrothermal fields, on- and off-ridge of the back-arc spreading centre of the SMT. 16S rRNA gene clone libraries for bacterial and archaeal communities were constructed from the fluid samples collected from the boreholes. Phylotypes related to Thiomicrospira in the Gammaproteobacteria (putative sulfide-oxidizers) and Mariprofundus in the Zetaproteobacteria (putative iron-oxidizers) were recovered from the fluid samples. A number of unique archaeal phylotypes were also recovered. Fluorescence in situ hybridization (FISH) analysis indicated the presence of active bacterial and archaeal populations in the fluids. The Zetaproteobacteria accounted for up to 32% of the total prokaryotic cell number as shown by FISH analysis using a specific probe designed in this study. Our results lead to the hypothesis that the Zetaproteobacteria play a role in iron oxidation within the oceanic crust.

Distribution and diversity of thermophilic sulfate-reducing bacteria within a Cu-Pb-Zn mine (Toyoha, Japan)

The distribution and diversity of thermophilic sulfate-reducing bacteria at the Cu-Pb-Zn Toyoha underground mine, Japan, were investigated using denaturing gradient gel electrophoresis analysis based on the 16S rRNA gene, and sequence analysis of the dissimilatory sulfite reductase gene. Hydrothermal waters from different boreholes penetrating the Cu-Pb-Zn sulfide veins were collected and concentrated with a sterile filter (pore size: 0.2 mum) at sites A (64 degrees C), B (71 degrees C), and C (48 degrees C). Microbial mats developed at sites A (53 degrees C), B (66 degrees C), and D (73 degrees C) were harvested. The denaturing gel electrophoresis analysis showed 17 bacterial and three archaeal bands including two of spore-forming, Gram-positive sulfate-reducing bacteria, Desulfotomaculum-like 16S rDNA sequences from site B. The phylogenetic analysis of 16 clone families of dissimilatory sulfite reductase genes indicated that they are Desulfotomaculum-, Thermodesulforhabdus-like sequences, and unresolved sequences. We obtained evidence of the diversity and distribution of microbes related to thermophilic sulfate-reducing bacteria within effluent-hydrothermal groundwater and microbial mats in the thermophilic subsurface environment of the Toyoha Mine.

Seafloor hydrothermal clay alteration at Jade in the back-arc Okinawa Trough: mineralogy, geochemistry and isotope characteristics

Seafloor hydrothermal activity at Jade has resulted in extensive alteration of the host epiclastic sediments and pumiceous tuffs, forming mica, kaolins (kaolinite and halloysite), Mg-rich chlorite, talc, montmorillonite, and a mixed-layer mineral of dioctahedral chlorite and montmorillonite (Chl/Mont). Clay mineral assemblages show a vertical variation, which reflects variable amounts of cold seawater incorporated into hot hydrothermal fluids in subsurface sediments and tuff. However, mixing alone cannot explain the occurrence of abundant kaolin minerals at Jade. The formation of kaolin minerals requires much more acidic fluid than expected from simple mixing of hydrothermal fluids and cold seawater. Low pH values are likely attained by oxidation of H2S either dissolved in the hydrothermal fluid or released from the fluid during decompression. The fluid reaching the seafloor is discharged into cold seawater, which caused precipitation of sulfides close to vents and native sulfur and barite at the margins of the vent areas. Halloysite, barite and anhydrite show Sr isotope compositions similar to marine Sr, indicating the derivation of marine Sr directly from seawater or by the dissolution of calcareous nannoplanktons. The isotopic compositions of kaolinite (δ18O = +7.4‰, δD = −23‰), Chl/Mont (δ18O = +7.0‰, δD = −32‰), and mica (δ18O = +5.4 to +9.9‰, δD = −30 to −26‰) suggest fluids of a heated seawater origin. The O isotopic data yielded formation temperatures of 170°C for kaolinite, 61 to 110°C for halloysite, and 145 to 238°C for mica. Barite δ34S values (+21.0 to +22.5‰) are very similar to the marine sulfate value, confirming that the barite formation took place due to mixing of Ba-bearing hydrothermal fluids and sulfate-rich seawater. Native sulfur shows a large variation in δ34S in one hand specimen probably because of rapid disequilibrium precipitation of S during fluid exhalation on the seafloor. Sulfur in hydrothermal fluids is usually consumed to form metal sulfides. Therefore, abundant native sulfur at Jade suggests high H2S/metals ratios of the hydrothermal fluids. The alteration assemblages and isotopic data of hydrothermal minerals from Jade are very similar to those of Kuroko-type barite deposits of middle Miocene age, which formed from fluids of high S/metals ratios at less than 200°C. At Jade, there is only one black smoker actively discharging high temperature (∼320°C) fluid, but there are many fossil sulfide chimneys and mounds in the area. The mineralogy and high Au and Cu in these precipitates suggest highly metalliferous hydrothermal activity in the past. These activities likely resulted in discharge of hydrothermal plumes and fall-outs of sulfides and sulfates on the seafloor. These fall-outs were incorporated in sediments far from the vent areas. They are now recorded as high metal contents in sediments with no petrographic and mineralogical evidence of in-situ hydrothermal activity. Some are high as 8,100 ppm for Cu, 12,500 ppm for Zn, 1,000 ppm for As, 100 ppm for Ag and 21,000 ppm for Pb. Detrital grains of montmorillonite in such sediments are coated with Fe-oxyhydroxides during the suspension in seawater before settling on the seafloor. The depths of such metal anomalies in sediments suggest high levels of metalliferous hydrothermal activities from 1,800 to 300 ybp.

Hydrothermal methane and manganese variation in the plume over the superfast-spreading southern East Pacific Rise

Abstract Onboard analyses of dissolved CH4 and Mn were conducted on the water column along the southern East Pacific Rise between 13 ° 50′ and 18°40′S during the 1993 RIDGE FLUX Cruise. Many hydrothermal plumes were identified by chemical anomalies which overlie more than half of the surveyed ridge crest. The CH 4 /Mn ratio in the plumes shows wide variability ranges from about 0.05 to 3.9 due to wide range of CH 4 concentration. The CH 4 -rich plumes were detected in the region of 16°00′—18°40′S where vigorous magmatic budget was confirmed by previous studies. Moreover, the CH 4 /Mn ratio of the plumes is highly correlated with other volatile/metal parameters such as the S/Fe ratio in plume particulate. These results strongly suggest that volatile input caused by magmatic perturbation to hydrothermal systems is responsible for the CH 4 /Mn variability in the southern EPR plumes, based on analogy of the case at the EPR 9°50′N site. The detection of several volatile-rich plumes and the extensive hydrothermal flux of volatile species are attributed to frequent magmatic events in the superfast spreading southern EPR.

Methylocaldum marinum sp. nov., a thermotolerant, methane-oxidizing bacterium isolated from marine sediments, and emended description of the genus Methylocaldum.

An aerobic, methane-oxidizing bacterium (strain S8(T)) was isolated from marine sediments in Kagoshima Bay, Japan. Phylogenetic analysis based on 16S rRNA gene sequences indicated that this strain is closely related to members of the genus Methylocaldum (97.6-97.9 % similarity) within the class Gammaproteobacteria. Strain S8(T) was a Gram-staining-negative, non-motile, coccoid or short rod-shaped organism. The temperature range for growth of strain S8(T) was 20-47 °C (optimum growth at 36 °C). It required NaCl (>0.5 %), tolerated up to 5 % NaCl and utilized methane and methanol. The major cellular fatty acid and major respiratory quinone were C16 : 0 and 18-methylene ubiquinone 8, respectively. The DNA G+C content was 59.7 mol%. Strain S8(T) possessed mmoX, which encodes soluble methane monooxygenase, as well as pmoA, which encodes the particulate methane monooxygenase. On the basis of this morphological, physiological, biochemical and genetic information, the first marine species in the genus Methylocaldum is proposed, with the name Methylocaldum marinum sp. nov. The type strain is S8(T) ( = NBRC 109686(T) = DSM 27392(T)). An emended description of the genus Methylocaldum is also provided.

Amino acids in the 308°C deep-sea hydrothermal system of the Suiyo Seamount, Izu-Bonin Arc, Pacific Ocean

Abstract Deep-sea hydrothermal systems are of significant interest as a new scientific frontier in a number of fields. This report analyzes data obtained in ocean-drilling surveys at submarine hydrothermal vents on the Suiyo Seamount in the Izu-Bonin Arc, Pacific Ocean. These surveys obtained direct data regarding subjacent extreme environments under extreme conditions of 308°C and greater than 14 MPa. Evaluation of the vertical distribution and stereochemistry of amino acids in such a vigorous hydrothermal system leads to a model of deep-sea subterranean chemistry and biology that describes a lack of evidence of abiotically synthesized amino acids. Large enantiomeric excesses of L -form amino acids supported the existence of a vigorous subjacent microbial oasis in a hydrothermal system.

Thermanaeromonas toyohensis gen. nov., sp. nov., a novel thermophilic anaerobe isolated from a subterranean vein in the Toyoha Mines

A novel thermophilic, strictly anaerobic, thiosulfate-reducing bacterium, designated strain ToBE(T), was isolated from a geothermal aquifer at a depth of 550 m in the Toyoha Mines (Hokkaido, Japan). The cells of this bacterium were rod-shaped (0.6 x 2.6 microm), non-motile and sporulating. Strain ToBE(T) was able to grow on formate, lactate, pyruvate or various sugars in the presence of thiosulfate as an electron acceptor. The strain could grow at 55-73 degrees C and pH 5.5-8.5. The optimum temperature and pH for the growth were 70 degrees C and pH 6.5. The G+C content of the DNA was 49.6 mol %. The major quinone and cellular fatty acids were respectively menaquinone-7 and iso-C15:0 and iso-C17:0. Analysis of the 16S rDNA revealed that the isolate was a member of the gram-positive bacteria and was related to the genus Thermoanaerobacter. However, the phylogenetic tree showed that the strain was distant from any other known bacteria, with sequence similarities of less than 90%. On the basis of phenotypic features and phylogenetic analysis, the name Thermanaeromonas toyohensis gen. nov., sp. nov., is proposed for the isolate, with strain ToBE(T) (= DSM 14490T = JCM 11376T) as the type strain.

Experimental verification of photostability for free- and bound-amino acids exposed to γ-rays and UV irradiation

The photo-stability of simulated free and bound amino acids exposed to photon sources of 1.2–1.3 MeV γ-rays from a 60C° source and ultra-violet (UV) irradiation from a 10 eV deuterium lamp was examined. The free amino acids in aqueous solution were drastically decreased while the bound amino acids in aqueous solution were slightly decreased with the duration of γ-rays and UV irradiation. The apparent half-lives (t1/2) of bound serine and threonine under γ-rays irradiation were more than 10.6 and 27.9 times as stable as the free amino acids, respectively. The photo-stability of bound amino acids was greater than that of free amino acids under irradiation by high-energy photons. These results strongly suggest that bound, but not free, amino acids could be found in extraterrestrial environments. Radio- or photo-alteration processes are mainly decomposition pathways, with the production of secondary amino acids via decomposition of the α-carboxylic group; β-alanine and γ-aminobutyric acids, α-decarboxylation products of aspartic acid and glutamic acid, respectively, were detected.