Eastern Lau Spreading Center Research Articles

Methanocaldococcus lauensis sp. nov., a novel deep-sea hydrothermal vent hyperthermophilic methanogen.

Three hyperthermophilic methanogens, designated strain SG7T, strain SG1 and strain SLH, were isolated from the ABE and Tu’i Malila deep-sea hydrothermal vent fields along the Eastern Lau Spreading Center. Phylogenetic analysis based on 16S rRNA gene sequence indicated that strains SG7T, SG1 and SLH were affiliated with the genus Methanocaldococcus within the family Methanocaldococcaceae , order Methanococcales . They shared 95.5–99.48 % 16S rRNA gene sequence similarity to other Methanocaldococcus species and were most closely related to Methanocaldococcus bathoardescens . Cells of strains SG7T, SG1 and SLH were cocci, with a diameter of 1.0–2.2 µm. The three strains grew between 45 and 93 °C (optimum, 80–85 °C), at pH 5.0–7.1 (optimum pH 6.2) and with 10–50 g l−1 NaCl (optimum 20–25 g l−1). Genome analysis revealed the presence of a 5.1 kbp plasmid in strain SG7T. Based on the results of average nucleotide identity and digital DNA–DNA hybridization analyses, we propose that strains SG1 and SG7T are representatives of a novel species, for which the name Methanocaldococcus lauensis sp. nov. is proposed; the type strain is SG7T (=DSM 109608T=JCM 39049T).

Hydrothermal activity and associated subsurface processes at Niuatahi rear-arc volcano, North East Lau Basin, SW Pacific: Implications from trace elements and stable isotope systematics in vent fluids

Hydrothermal activity is abundant in the area between the North Eastern Lau Spreading Center and the Tofua intra-oceanic island arc with multiple active sites in the rear-arc at the Mata and Niuatahi volcanoes. We report geochemical data for high-temperature vent fluids sampled from within the caldera of Niuatahi volcano. Hydrothermal fluids were sampled from three vent sites: South Central, Southwestern Cone and Northern Cone located in water depths between 1607 and 1699 m. Maximum temperatures of 334 °C were measured and pH values were as low as 2.8. The vent fluids were characterized by depletions in Mg, SO4 and U as well as an enrichment of (trace) metals (e.g., Fe, Mn, K, Li) and dissolved gases (e.g., H2S, CO2, H2) relative to seawater. Water-rock ratios calculated based on concentrations (K, Li, Rb, Cs, REE) and isotope ratios (δ7Li, δ11B, 87Sr/86Sr) suggest fluid-rock interactions under rock-dominated conditions at all three vent sites.The South Central vents lie closest to the site of most recent volcanic activity in the Niuatahi caldera. Vent fluids are characterized by relatively low Cl concentrations (as low as 292 mmol/kg) that are indicative of sub-critical phase separation. These fluids also had the lowest pH values (2.8–3.1), highest H2S and lowest H2, CH4 and CO2 concentrations of the three sites. The δD and δ18O values suggest that H2O and CO2 were added in small amounts by subduction-related volcanic vapors. However, there was no evidence for magmatic SO2 input in the vent fluids at the time of sampling in 2018. Vent fluids from the Northern and Southwestern Cone sites on the caldera ring fault had a similar chemical composition, despite being situated at opposite sides of the caldera. Fluids from these sites had lower Fe/Mn ratios (<1) and H2S concentrations than those from South Central suggesting that they were affected by subsurface cooling and sulfide precipitation. This study indicates variations of the Niuatahi hydrothermal vent sites depending on the location within the caldera with variable effects of fluid-rock interaction and magmatic input on fluid compositions in agreement with previous work on fluid S isotopes and sulfides.

Hydrothermal vent periphery invertebrate community habitat preferences of the Lau Basin

The Eastern Lau Spreading Center (ELSC), located between 19°20′S and 22°45′S, is a back-arc basin containing active hydrothermal vents, and is characterized by gradients of several geological and chemical variables that follow along the north – south axis. The northern section of the ELSC spreads faster than the southern section resulting in farther distance from the Tofua Arc and vent geology and chemistry more akin to mid-oceanic ridges. In the southern section, where distance from the arc is less, substrates are more heavily influenced by water resulting in andesitic substrates as opposed to the basaltic substrates in the north. There are also north to south biological patterns; vent peripheral zone communities in the northern area are dominated by anemones, and in the southern area, by sponges. This project used a replacement type experiment to test whether the anemone and sponge community distributions are due to substrate preferences (basalt or andesite) or location effects. In September 2006, 17 basalt and 18 andesite rock blocks were set out in the peripheral vent zone at three locations in the Lau Basin; 42 months later, in May 2009, the rocks were recovered. After rock block collection, communities that had colonized them were defined by identifying all invertebrates to lowest taxonomic level possible. As expected, basalt rock blocks were smoother than andesite rock blocks, but they were also smaller, though this was ameliorated by even distribution at experimental locations. Rock type did not affect the invertebrate community, but location did; the location specific effect that impacted the invertebrate community may have been sulfide concentration. The seafloor at southern locations was more brecciated, allowing sulfide to distribute farther laterally, which could result in enhanced primary productivity, and thus influence the observed community differences. We conclude that in peripheral vent habitats, energy availability for primary production and food availability are more important in structuring communities than the type of rock substrate.

Trace Element and Isotope Systematics in Vent Fluids and Sulphides From Maka Volcano, North Eastern Lau Spreading Centre: Insights Into Three-Component Fluid Mixing

Back-arc spreading centres and related volcanic structures are known for their intense hydrothermal activity. The axial volcanic edifice of Maka at the North Eastern Lau Spreading Centre is such an example, where fluids of distinct composition are emitted at the Maka hydrothermal field (HF) and at Maka South in 1,525–1,543 m water depth. At Maka HF black smoker-type fluids are actively discharged at temperatures of 329°C and are characterized by low pH values (2.79–3.03) and a depletion in Mg (5.5 mmol/kg) and SO4 (0.5 mmol/L) relative to seawater. High metal (e.g., Fe up to ∼6 mmol/kg) and rare Earth element (REE) contents in the fluids, are indicative for a rock-buffered hydrothermal system at low water/rock ratios (2–3). At Maka South, venting of white smoke with temperatures up to 301°C occurs at chimneys and flanges. Measured pH values range from 4.53 to 5.42 and Mg (31.0 mmol/kg), SO4 (8.2 mmol/L), Cl (309 mmol/kg), Br (0.50 mmol/kg) and Na (230 mmol/kg) are depleted compared to seawater, whereas metals like Li and Mn are typically enriched together with H2S. We propose a three-component mixing model with respect to the fluid composition at Maka South including seawater, a boiling-induced low-Cl vapour and a black smoker-type fluid similar to that of Maka HF, which is also preserved by the trace element signature of hydrothermal pyrite. At Maka South, high As/Co (&amp;gt;10–100) and Sb/Pb (&amp;gt;0.1) in pyrite are suggested to be related to a boiling-induced element fractionation between vapour (As, Sb) and liquid (Co, Pb). By contrast, lower As/Co (&amp;lt;100) and a tendency to higher Co/Ni values in pyrite from Maka HF likely reflect the black smoker-type fluid. The Se/Ge ratio in pyrite provides evidence for fluid-seawater mixing, where lower values (&amp;lt;10) are the result of a seawater contribution at the seafloor or during fluid upflow. Sulphur and Pb isotopes in hydrothermal sulphides indicate a common metal (loid) source at the two vent sites by host rock leaching in the reaction zone, as also reflected by the REE patterns in the vent fluids.

Copepod assemblages along a hydrothermal stress gradient at diffuse flow habitats within the ABE vent site (Eastern Lau Spreading Center, Southwest Pacific)

Copepoda is the most diverse and abundant taxon at deep-sea hydrothermal vents, contributing significantly to the biodiversity and thus is important in maintaining ecosystem functioning. To date we lack knowledge on meiofauna, specifically copepod community dynamics, in the entire region of the Eastern Lau Spreading Center. We explore abundance and diversity of copepods associated with foundation species thriving at distinct physiochemical regimes at the active vent site ABE. Diffuse flow habitats within ABE are dominated by three foundation species: (1) the snail Alviniconcha hessleri, exposed to average vent fluid temperatures of ~24 °C, (2) the snail Ifremeria nautilei at ~12 °C, and (3) the mussel Bathymodiolus septemdierum in average temperatures of ~6 °C. In each habitat, three samples were taken using a quantitative collection device (mussel-pot). Copepod abundance ranged from 1 to 30 ind. per 10 cm2, with no significant differences between the three habitats. A total of 18 copepod species were identified. In the Alviniconcha habitat, the vent endemic dirivultid copepod Stygiopontius lauensis dominated the community, representing >90% of the individuals. Species richness and Shannon diversity were significantly higher in the Bathymodiolus habitat, correlated with lower temperatures, lower hydrogen sulfide concentrations and higher oxygen concentrations. This increase in diversity was driven by a community mostly comprised of habitat generalists including genera reported from shallow coastal waters, shallow vents, and peripheral vent environments. This study provides the first quantification of biodiversity and community structure of copepods along a physiochemical stress gradient at a relatively stable Southwest Pacific vent site prospective for deep-sea mining.

A multi-modal approach to measuring particulate iron speciation in buoyant hydrothermal plumes

Processes active within buoyant hydrothermal plumes are expected to modulate the flux of elements, such as Fe, to the deep ocean; however, they are yet to be described in a comprehensive manner through observations or models. In this study, we compare observed particulate Fe (pFe) speciation with thermodynamic (equilibrium) reaction path modeling for three vent fields in the Eastern Lau Spreading Center (ELSC). At each site, particles were collected from the buoyant rising portion of hydrothermal plumes using in situ filtration with a Remotely Operated Vehicle. Filter bound particles were analyzed by synchrotron micro-probe X-ray fluorescence mapping (XRF), X-ray diffraction (XRD), XRF spectroscopy, and X-ray absorption near edge structure (XANES) spectroscopy at the Fe 1 s edge, as well as XRF-based chemical speciation mapping for Fe. For buoyant plumes of the ELSC, diversity in solid-state chemistry was high, and poorly crystalline, meta-stable phases were common. We demonstrate that to fully describe the crystalline-to-noncrystalline character of plume pFe, a multi-modal XRD-XANES analytical approach is needed. We found that an equilibrium modeling approach worked well for pyrite but performed poorly for important families of meta-stable pFe, namely Fe (oxyhydr)oxides and monosulfides. Based on our findings, we recommend future field expeditions strategically explore sites representing a diversity of site-specific conditions to better capture the full range of processes active in plumes. We also recommend development of kinetic models, as well as expansion of thermodynamic databases to better reflect the solid-state composition of plumes. These steps should allow oceanographers to understand the processes controlling Fe speciation in plumes well enough to create realistic models of hydrothermal fluxes to the ocean.

Uppermost crustal structure across the eastern Lau spreading center from P-to-S converted waves

P and S wave data from the L-SCAN active-source wide-angle reflection/refraction experiment are modelled to investigate upper crustal structure in the Lau backarc basin. A combination of ray tracing and finite difference numerical wavefield simulation is used to identify P and P-to-S converted seismic phases. The phases primarily arise from two shallow interfaces, one at ~ 80 m depth or less, and the other at 500–650 m depth. The shallower interface is deeper than the sediment base, is observed across the study area, and is interpreted as a ‘layer 2Aa’ boundary, proposed to result from a rapid change in crack density. The deeper interface is interpreted as the layer 2A–2B boundary, corresponding to a transition from lavas to sheeted dykes. Layer 2A, on average, is 150 m thicker in crust that formed at the spreading center when spreading was located near the arc ( 70 km away). Layer 2A thickness and Vp/Vs values indicate that a thicker and more porous lava layer, dominated by basalts to basalt-andesites, cap near-arc crust, while a thinner and less-porous, mostly basaltic, volcanic layer caps the far-arc crust. These results are consistent with the waning influence of slab-derived volatiles on crustal formation as seafloor spreading moves away from the active arc.

Hafnium isotope constraints on the nature of the mantle beneath the Southern Lau basin (SW Pacific)

New Hf isotope data provide new insights into the nature of the mantle beneath the southern Lau basin, adding new constraints on the displacement process of the Pacific mid-ocean ridge basalt (MORB)-type mantle by the Indian MORB-type mantle. The Hf isotopic ratios (176Hf/177Hf) of submarine lavas from the eastern Lau spreading center (ELSC) range from 0.283194 (εHf = 14.92) to 0.283212 (εHf = 15.54), with an average value of 0.283199 (εHf = 15.11) whereas those from the Valu Fa ridge (VFR) vary from 0.283221 (εHf = 15.88) to 0.283200 (εHf = 15.14), with an average of 0.283214 (15.61), indicating that ELSC lavas have a slightly more radiogenic Hf isotopic composition than VFR lavas. In contrast to the results from previous studies, the new Hf analyses combined with previous Nd isotope data clearly show that both VFR and ELSC have the distinct Hf–Nd isotope composition of the so-called DUPAL isotopic anomaly in the Indian MORB-type mantle. The DUPAL isotopic signature at VFR demonstrates for the first time that the inflow of the Indian MORB-type mantle has reached the southern tip of tectonic propagation in the southern Lau basin.

Trace element proxies of seafloor hydrothermal fluids based on secondary ion mass spectrometry (SIMS) of black smoker chimney linings

Sampling of paired black smoker chimney linings and seafloor hydrothermal vent fluids supports the development of trace element proxies for sulfide mineral deposition environments by facilitating analyses of trace element partitioning between mineral and fluid phases under well-constrained physiochemical conditions. Here, concentrations of Co, Ni, Ga, Ag, and In in chalcopyrite lining 22 black smoker chimneys (29 for Co, Ag, and In) are measured using secondary ion mass spectrometry (SIMS) calibrated against inductively coupled plasma mass spectrometry (ICP-MS) and NIST-traceable reference solutions. To provide additional data on the trace element concentrations of vent fluid pairs for 19 of the 29 black smoker chimney linings investigated, this paper also presents new ICP-MS data for 33 hydrothermal vent fluids collected from the Tahi Moana-1, ABE, Tu’i Malila, and Mariner vent fields on the Eastern Lau Spreading Center and Valu Fa Ridge.The chalcopyrite black smoker chimney linings investigated represent a variety of temperature (269–395 °C), chemical (e.g., pH (at 25 °C) = 2.3–4.4), and geologic conditions. Electron microprobe results indicate that mineral stoichiometry ranges from stoichiometric chalcopyrite to mol Cu : mol Fe = 0.65. Trace element concentrations obtained by SIMS are: Co (<2 ng/g–760 μg/g), Ni (<17 ng/g–454 μg/g), Ga (<0.9 ng/g–48 μg/g), Ag (60 μg/g–3800 μg/g), In (<0.5 ng/g–270 μg/g). Concentrations of Ag in chalcopyrite strongly correlate with the free ion activity ratio of {Ag+}:{Cu+} in paired vent fluids, with high Ag concentrations in chalcopyrite indicating formation from near neutral vent fluids containing low Cu concentrations or low-pH vent fluids with high Ag concentrations attributable to subsurface Ag remobilization. Chalcopyrite with low Ag precipitates from low-pH Cu-rich fluids unaffected by extensive Ag remobilization. Concentrations of Ga and In in chalcopyrite exhibit a negative trend with vent fluid pH, possibly reflecting the strength of Ga and In OH− complexes. Thus, Ga and In concentrations differentiate Ag-rich chalcopyrite formed from near-neutral Cu-poor vent fluids or that formed from Ag-rich low-pH vent fluids. In contrast, Co and Ni exhibit no trend with fluid data, but correlate with mineral Cu:Fe ratios, possibly reflecting the greater availability of Fe(II) lattice sites or paired substitution of 2+ ions.Overall, this study demonstrates the potential of paired vent fluid and black smoker chimney samples to provide insight into the partitioning of trace elements in sulfide mineral deposition environments and related proxies of important fluid parameters such as pH and metal concentrations. This study also demonstrates the utility of SIMS to precisely analyze trace elements in chalcopyrite at high spatial resolutions and low detection limits.

Deep-sea hydrothermal vent metagenome-assembled genomes provide insight into the phylum Nanoarchaeota.

Ectosymbiotic Nanoarchaeota live on the surface of diverse archaeal hosts. Despite being broadly distributed in global geothermal systems, only three Nanoarchaeota have been successfully co-cultivated with their hosts, and until now no nanoarchaeotal cultures or genomes have been described from deep-sea hydrothermal vents. We recovered three nanoarchaeotal metagenome-assembled genomes (MAGs) from deep-sea hydrothermal vent sites at the Eastern Lau Spreading Center (M10-121), Guaymas Basin (Gua-46) and the Mid-Cayman Rise (MC-1). Based on average amino acid identity analysis, M10-121 is a novel species in the candidate genus Nanoclepta, while the other two MAGs represent novel genera in the Nanoarchaeota. Like previously sequenced Nanoarchaeota, each MAG encodes at least one split protein-coding gene. The MAGs also contain a mosaic of key nanoarchaeotal features, including CRISPR repeat regions and marker genes for gluconeogenesis and archaeal flagella. MC-1 also encodes the pentose bisphosphate pathway, which may allow the nanoarchaeote to bypass several steps in glycolysis and produce ATP.

Marinitoga lauensis sp. nov., a novel deep-sea hydrothermal vent thermophilic anaerobic heterotroph with a prophage

A novel moderately thermophilic, heterotrophic anaerobe, designated strain LG1T, was isolated from the Mariner deep-sea hydrothermal vent field along the Eastern Lau Spreading Center and Valu Fa Ridge. Cells of strain LG1T were motile rods, occurring singly or in pairs, 0.6μm in width and 1.2μm in length. The strain LG1T grew between 40 and 70°C (optimum 50–55°C), at a pH between 5 and 8 (optimum pH 6.5) and with 7.5–50gL−1 NaCl (optimum 30gL−1). Sulfur, cystine and thiosulfate were reduced to sulfide, and cell yield was improved in the presence of cystine. Strain LG1T was an organotroph able to use a variety of organic compounds. Phylogenetic analysis based on 16S rRNA gene sequence comparisons indicated that strain LG1T was affiliated to the genus Marinitoga within the order Petrotogales. It shared 95.34–96.31% 16S rRNA gene sequence similarity with strains of other Marinitoga species, and is most closely related to Marinitoga okinawensis. Genome analysis revealed the presence of a prophage sharing high sequence homology with the viruses MPV1, MCV1 and MCV2 hosted by Marinitoga strains. Based on the data from the phylogenetic analyses and the physiological properties of the novel isolate, we propose that strain LG1T is a representative of a novel species, for which the name Marinitoga lauensis sp. nov. is proposed; the type strain is LG1T (=DSM 106824=JCM 32613).

Geochemistry of diverse lava types from the Lau Basin (South West Pacific): Implications for complex back‐arc mantle dynamics

Lavas from back‐arc basins are generally diverse, and their geochemical compositions indicate that they received variable contributions from subduction components during petrogenesis. Obtaining comprehensive geochemistry characteristics for the entire back‐arc basin are helpful in gaining a better understanding of the complexities of back‐arc evolution. In this study, we systematically reviewed the major and trace element compositions of Lau Basin lavas. This data set covered all of the major tectonic units of the basin, for example, the Eastern Lau spreading center (ELSC), the Valu Fa ridge (VFR), the Central Lau spreading center (CLSC), the Northwestern Lau spreading center (NWLSC), the Northeastern Lau spreading center (NELSC), the Mangatolu Triple Junction (MTJ), and the Fonualei Spreading Center (FSC). The lava types from these locations are diverse, including tholeiitic basalts, alkali basalts, basaltic andesites, andesites, dacites, and rhyolites. In addition, the NELSC and FSC contain boninites. In this study, the geochemical compositions of these diverse rock types are used to investigate the spreading dynamics of the Lau Basin back‐arc. We conclude that (a) the subduction components mainly include hydrous fluids released from the subducted slab, and hydrous melt directly from the melting subducted sediment, and the influence of the subducted components on the mantle wedge and the petrogenesis of the central and southern Lau Basin lavas decreases with increasing distance from the Tonga Trench; (b) during the propagation and spreading of the Samoan mantle into the Lau Basin, lavas from the NELSC, NWLSC, MTJ, and even from the northern part of the FSC may receive variable degrees of influence from the Samoan plume; and (c) the migration of Indian MORB‐like mantle southwards into the Pacific mantle is consistent with the opening of the Lau Basin. With the gradual migration of Indian mantle into the Lau Basin, a series of spreading centers were formed, for example, in order, the NWLSC, CLSC, ELSC, and the propagating VFR.

A graphical tool for the quantitative assessment of gait control performance: Analysis of maturation and dual task effects

This study investigates the morphology, mineralogy, and geochemistry of seafloor massive sulfide (SMS) deposits from six back-arc hydrothermal vent fields along the Eastern Lau Spreading Center (ELSC) and Valu Fa Ridge (VFR) in the context of endmember vent fluid chemistry and proximity to the Tonga Subduction Zone. To complement deposit geochemistry, vent fluid analyses of Cu, Zn, Ba, Pb and H2,(aq) were completed to supplement existing data and enable thermodynamic calculations of mineral saturation states at in situ conditions. Results document southward increases in the abundance of mantle-incompatible elements in hydrothermal fluids (Ba and Pb) and SMS deposits (Ba, Pb, As, and Sb), which is also expressed in the abundance of barite (BaSO4) and galena (PbS) in SMS deposits. These increases correspond to a decrease in distance between the ELSC/VFR and the Tonga Subduction Zone that correlates with a change in crustal lithology from back-arc basin basalt in the north to mixed andesite, rhyolite, and dacite in the south. Barite influences deposit morphology, contributing to the formation of horizontal flanges and squat terraces. Results are also consistent with a regional-scale lowering of hydrothermal reaction zone temperatures from north to south (except at the southernmost Mariner vent field) that leads to lower-temperature, higher-pH vent fluids relative to mid-ocean ridges of similar spreading rates (Mottl et al., 2011). These fluids are Cu- and Zn-poor and the deposits formed from these fluids are Cu-poor but Zn-rich. In contrast, at the Mariner vent field, higher-temperature and lower pH vent fluids are hypothesized to result from higher reaction zone temperatures and the localized addition of acidic magmatic volatiles (Mottl et al., 2011). The Mariner fluids are Cu- and Zn-rich and vent from SMS deposits that are rich in Cu but poor in Zn with moderate amounts of Pb. Thermodynamic calculations indicate that the contrasting metal contents of vent fluids and SMS deposits can be accounted for by vent fluid pH. Wurtzite/sphalerite ((Zn, Fe)S) and galena (PbS) are saturated at higher temperatures in higher-pH, Zn-, Cu-, and Pb-poor ELSC/VFR vent fluids, but are undersaturated at similar temperatures in low-pH, Zn-, Cu-, and Pb-rich vent fluids from the Mariner vent field.Indicators of pH in the ELSC and VFR SMS deposits include the presence of co-precipitated wurtzite and chalcopyrite along conduit linings in deposits formed from higher pH fluids, and different correlations between concentrations of Zn and Ag in bulk geochemical analyses. Significant positive bulk geochemical Zn:Ag correlations occur for deposits at vent fields where hydrothermal fluids have a minimum pH (at 25 °C) < 3.3, while correlations of Zn:Ag are weak or negative for deposits at vent fields where the minimum vent fluid pH (at 25 °C) > 3.6. Data show that the compositions of the mineral linings of open conduit chimneys (minerals present, mol% FeS in (Zn,Fe)S) that precipitate directly from hydrothermal fluids closely reflect the temperature and sulfur fugacity of sampled hydrothermal fluids. These mineral lining compositions thus can be used as indicators of hydrothermal fluid temperature and composition (pH, metal content, sulfur fugacity).

Thermosulfuriphilus ammonigenes gen. nov., sp. nov., a thermophilic, chemolithoautotrophic bacterium capable of respiratory ammonification of nitrate with elemental sulfur.

An extremely thermophilic, anaerobic, chemolithoautotrophic bacterium (strain ST65T) was isolated from a deep-sea hydrothermal vent chimney located on the Eastern Lau Spreading Centre in the south-western Pacific Ocean, at a depth of 1870 m. Cells of strain ST65T were non-motile straight or slightly curved short rods, 0.5-0.6 µm in diameter and 0.8-1.5 µm in length. The temperature range for growth was 47-75 °C, with an optimum at 65 °C. The pH range for growth was 5.5-7.5, with an optimum at pH 6.5. Growth of strain ST65T was observed at NaCl concentrations ranging from 1.5 to 4.5 % (w/v), with an optimum at 2.0-2.5 %. Strain ST65T grew anaerobically with inorganic carbon as a carbon source and with elemental sulfur as an electron donor and nitrate as an electron acceptor producing sulfate and ammonium. It was also able to grow by disproportionation of elemental sulfur, thiosulfate and sulfite. Sulfate was not utilized as an electron acceptor. Analysis of the 16S rRNA gene sequence revealed that the isolate belongs to a deep lineage in the phylum Thermodesulfobacteria. On the basis of its physiological properties and results of phylogenetic analyses, it is proposed that the isolate represents a novel species of a new genus, Thermosulfuriphilus ammonigenes gen. nov., sp. nov. ST65T (=DSM 102941T=VKM B-2855T) is the type strain of the type species.

Influences of the Tonga Subduction Zone on seafloor massive sulfide deposits along the Eastern Lau Spreading Center and Valu Fa Ridge

This study investigates the morphology, mineralogy, and geochemistry of seafloor massive sulfide (SMS) deposits from six back-arc hydrothermal vent fields along the Eastern Lau Spreading Center (ELSC) and Valu Fa Ridge (VFR) in the context of endmember vent fluid chemistry and proximity to the Tonga Subduction Zone. To complement deposit geochemistry, vent fluid analyses of Cu, Zn, Ba, Pb and H2,(aq) were completed to supplement existing data and enable thermodynamic calculations of mineral saturation states at in situ conditions. Results document southward increases in the abundance of mantle-incompatible elements in hydrothermal fluids (Ba and Pb) and SMS deposits (Ba, Pb, As, and Sb), which is also expressed in the abundance of barite (BaSO4) and galena (PbS) in SMS deposits. These increases correspond to a decrease in distance between the ELSC/VFR and the Tonga Subduction Zone that correlates with a change in crustal lithology from back-arc basin basalt in the north to mixed andesite, rhyolite, and dacite in the south. Barite influences deposit morphology, contributing to the formation of horizontal flanges and squat terraces. Results are also consistent with a regional-scale lowering of hydrothermal reaction zone temperatures from north to south (except at the southernmost Mariner vent field) that leads to lower-temperature, higher-pH vent fluids relative to mid-ocean ridges of similar spreading rates (Mottl et al., 2011). These fluids are Cu- and Zn-poor and the deposits formed from these fluids are Cu-poor but Zn-rich. In contrast, at the Mariner vent field, higher-temperature and lower pH vent fluids are hypothesized to result from higher reaction zone temperatures and the localized addition of acidic magmatic volatiles (Mottl et al., 2011). The Mariner fluids are Cu- and Zn-rich and vent from SMS deposits that are rich in Cu but poor in Zn with moderate amounts of Pb. Thermodynamic calculations indicate that the contrasting metal contents of vent fluids and SMS deposits can be accounted for by vent fluid pH. Wurtzite/sphalerite ((Zn, Fe)S) and galena (PbS) are saturated at higher temperatures in higher-pH, Zn-, Cu-, and Pb-poor ELSC/VFR vent fluids, but are undersaturated at similar temperatures in low-pH, Zn-, Cu-, and Pb-rich vent fluids from the Mariner vent field.Indicators of pH in the ELSC and VFR SMS deposits include the presence of co-precipitated wurtzite and chalcopyrite along conduit linings in deposits formed from higher pH fluids, and different correlations between concentrations of Zn and Ag in bulk geochemical analyses. Significant positive bulk geochemical Zn:Ag correlations occur for deposits at vent fields where hydrothermal fluids have a minimum pH (at 25°C)<3.3, while correlations of Zn:Ag are weak or negative for deposits at vent fields where the minimum vent fluid pH (at 25°C)>3.6. Data show that the compositions of the mineral linings of open conduit chimneys (minerals present, mol% FeS in (Zn,Fe)S) that precipitate directly from hydrothermal fluids closely reflect the temperature and sulfur fugacity of sampled hydrothermal fluids. These mineral lining compositions thus can be used as indicators of hydrothermal fluid temperature and composition (pH, metal content, sulfur fugacity).

Mitochondrial DNA Analyses Indicate High Diversity, Expansive Population Growth and High Genetic Connectivity of Vent Copepods (Dirivultidae) across Different Oceans

Communities in spatially fragmented deep-sea hydrothermal vents rich in polymetallic sulfides could soon face major disturbance events due to deep-sea mineral mining, such that unraveling patterns of gene flow between hydrothermal vent populations will be an important step in the development of conservation policies. Indeed, the time required by deep-sea populations to recover following habitat perturbations depends both on the direction of gene flow and the number of migrants available for re-colonization after disturbance. In this study we compare nine dirivultid copepod species across various geological settings. We analyze partial nucleotide sequences of the mtCOI gene and use divergence estimates (FST) and haplotype networks to infer intraspecific population connectivity between vent sites. Furthermore, we evaluate contrasting scenarios of demographic population expansion/decline versus constant population size (using, for example, Tajima’s D). Our results indicate high diversity, population expansion and high connectivity of all copepod populations in all oceans. For example, haplotype diversity values range from 0.89 to 1 and FST values range from 0.001 to 0.11 for Stygiopontius species from the Central Indian Ridge, Mid Atlantic Ridge, East Pacific Rise, and Eastern Lau Spreading Center. We suggest that great abundance and high site occupancy by these species favor high genetic diversity. Two scenarios both showed similarly high connectivity: fast spreading centers with little distance between vent fields and slow spreading centers with greater distance between fields. This unexpected result may be due to some distinct frequency of natural disturbance events, or to aspects of individual life histories that affect realized rates of dispersal. However, our statistical performance analyses showed that at least 100 genomic regions should be sequenced to ensure accurate estimates of migration rate. Our demography parameters demonstrate that dirivultid populations are generally large and continuously undergoing population growth. Benthic and pelagic species abundance data support these findings.

Crustal shear velocity structure in the Southern Lau Basin constrained by seafloor compliance

AbstractSeafloor morphology and crustal structure vary significantly in the Lau back‐arc basin, which contains regions of island arc formation, rifting, and seafloor spreading. We analyze seafloor compliance: deformation under long period ocean wave forcing, at 30 ocean bottom seismometers to constrain crustal shear wave velocity structure along and across the Eastern Lau Spreading Center (ELSC). Velocity models obtained through Monte Carlo inversion of compliance data show systematic variation of crustal structure in the basin. Sediment thicknesses range from zero thickness at the ridge axis to 1400 m near the volcanic arc. Sediment thickness increases faster to the east than to the west of the ELSC, suggesting a more abundant source of sediment near the active arc volcanoes. Along the ELSC, upper crustal velocities increase from the south to the north where the ridge has migrated farther away from the volcanic arc front. Along the axial ELSC, compliance analysis did not detect a crustal low‐velocity body, indicating less melt in the ELSC crustal accretion zone compared to the fast spreading East Pacific Rise. Average upper crust shear velocities for the older ELSC crust produced when the ridge was near the volcanic arc are 0.5–0.8 km/s slower than crust produced at the present‐day northern ELSC, consistent with a more porous extrusive layer. Crust in the western Lau Basin, which although thought to have been produced through extension and rifting of old arc crust, is found to have upper crustal velocities similar to older oceanic crust produced at the ELSC.

Peripheral communities of the Eastern Lau Spreading Center and Valu Fa Ridge: community composition, temporal change and comparison to near‐vent communities

AbstractWestern Pacific hydrothermal vents will soon be subjected to deep‐sea mining and peripheral sites are considered the most practical targets. The limited information on community dynamics and temporal change in these communities makes it difficult to anticipate the impact of mining activities and recovery trajectories. We studied community composition of peripheral communities along a cline in hydrothermal chemistry on the Eastern Lau Spreading Center and Valu Fa Ridge (ELSC‐VFR) and also studied patterns of temporal change. Peripheral communities located in the northern vent fields of the ELSC‐VFR are significantly different from those in the southern vent fields. Higher abundances of zoanthids and anemones were found in northern peripheral sites and the symbiont‐containing mussel Bathymodiolus brevior, brisingid seastars and polynoids were only present in the northern peripheral sites. By contrast, certain faunal groups were seen only in the southern peripheral sites, such as lollipop sponges, pycnogonids and ophiuroids. Taxonomic richness of the peripheral communities was similar to that of active vent communities, due to the presence of non‐vent endemic species that balanced the absence of species found in areas of active venting. The communities present at waning active sites resemble those of peripheral sites, indicating that peripheral species can colonize previously active vent sites in addition to settling in the periphery of areas of venting. Growth and mortality were observed in a number of the normally slow‐growing cladorhizid stick sponges, indicating that these animals may exhibit life history strategies in the vicinity of vents that differ from those previously recorded. A novel facultative association between polynoids and anemones is proposed based on their correlated distributions.

Metagenomic resolution of microbial functions in deep-sea hydrothermal plumes across the Eastern Lau Spreading Center.

Microbial processes within deep-sea hydrothermal plumes affect ocean biogeochemistry on global scales. In rising hydrothermal plumes, a combination of microbial metabolism and particle formation processes initiate the transformation of reduced chemicals like hydrogen sulfide, hydrogen, methane, iron, manganese and ammonia that are abundant in hydrothermal vent fluids. Despite the biogeochemical importance of this rising portion of plumes, it is understudied in comparison to neutrally buoyant plumes. Here we use metagenomics and bioenergetic modeling to describe the abundance and genetic potential of microorganisms in relation to available electron donors in five different hydrothermal plumes and three associated background deep-sea waters from the Eastern Lau Spreading Center located in the Western Pacific Ocean. Three hundred and thirty one distinct genomic 'bins' were identified, comprising an estimated 951 genomes of archaea, bacteria, eukarya and viruses. A significant proportion of these genomes is from novel microorganisms and thus reveals insights into the energy metabolism of heretofore unknown microbial groups. Community-wide analyses of genes encoding enzymes that oxidize inorganic energy sources showed that sulfur oxidation was the most abundant and diverse chemolithotrophic microbial metabolism in the community. Genes for sulfur oxidation were commonly present in genomic bins that also contained genes for oxidation of hydrogen and methane, suggesting metabolic versatility in these microbial groups. The relative diversity and abundance of genes encoding hydrogen oxidation was moderate, whereas that of genes for methane and ammonia oxidation was low in comparison to sulfur oxidation. Bioenergetic-thermodynamic modeling supports the metagenomic analyses, showing that oxidation of elemental sulfur with oxygen is the most dominant catabolic reaction in the hydrothermal plumes. We conclude that the energy metabolism of microbial communities inhabiting rising hydrothermal plumes is dictated by the underlying plume chemistry, with a dominant role for sulfur-based chemolithoautotrophy.

The uptake and excretion of partially oxidized sulfur expands the repertoire of energy resources metabolized by hydrothermal vent symbioses.

Symbiotic associations between animals and chemoautotrophic bacteria crowd around hydrothermal vents. In these associations, symbiotic bacteria use chemical reductants from venting fluid for the energy to support autotrophy, providing primary nutrition for the host. At vents along the Eastern Lau Spreading Center, the partially oxidized sulfur compounds (POSCs) thiosulfate and polysulfide have been detected in and around animal communities but away from venting fluid. The use of POSCs for autotrophy, as an alternative to the chemical substrates in venting fluid, could mitigate competition in these communities. To determine whether ESLC symbioses could use thiosulfate to support carbon fixation or produce POSCs during sulfide oxidation, we used high-pressure, flow-through incubations to assess the productivity of three symbiotic mollusc genera—the snails Alviniconcha spp. and Ifremeria nautilei, and the mussel Bathymodiolus brevior—when oxidizing sulfide and thiosulfate. Via the incorporation of isotopically labelled inorganic carbon, we found that the symbionts of all three genera supported autotrophy while oxidizing both sulfide and thiosulfate, though at different rates. Additionally, by concurrently measuring their effect on sulfur compounds in the aquaria with voltammetric microelectrodes, we showed that these symbioses excreted POSCs under highly sulfidic conditions, illustrating that these symbioses could represent a source for POSCs in their habitat. Furthermore, we revealed spatial disparity in the rates of carbon fixation among the animals in our incubations, which might have implications for the variability of productivity in situ. Together, these results re-shape our thinking about sulfur cycling and productivity by vent symbioses, demonstrating that thiosulfate may be an ecologically important energy source for vent symbioses and that they also likely impact the local geochemical regime through the excretion of POSCs.