Black Smoker Vents Research Articles

Trophic diversity of chemosymbiont hosts in deep-sea hydrothermal vents using amino acid nitrogen isotopes

Chemosymbiotic species inhabiting deep-sea hydrothermal vents are known to rely on microbial symbionts for nutrition. However, the relative contributions of heterotrophic energy sources to their diets remain poorly understood. In this study, we investigate the trophic positions (TP) of symbiont-bearing taxa, including vent mussels, snails, and shrimps, and examine the contribution of copepods and detrital organic matter (OM) to the food chain. Amino acid nitrogen isotopic compositions (δ15NAA) were used to investigate the TP of vent mussels (Bathymodiolus septemdierum and Gigantidas vrijenhoeki), snails (Alviniconcha spp.), and shrimps (Alvinocaris sp. and Rimicaris kairei) from two different vent environments. δ15NAA values in copepods and OM were also measured. Microbial resynthesis index (ΣV) was calculated to predict the contribution of reworked OM as an energy source to the hydrothermal vent ecosystem. Variations in TP were observed among vent mussels and snails from different vent environments, with higher TP in species from diffusing vents than in those from black smoker vents. Shrimps dwelling in a single diffusing vent exhibited distinct TP, suggesting that microhabitat and phylogeny may influence their energy acquisition. Notably, copepods occupied higher TPs than expected, possibly owing to the consumption of detrital OM. Our findings provide new insights into the trophic diversity of chemosymbiotic species in deep-sea hydrothermal vents and demonstrate the utility of δ15NAA analysis as a tool for unraveling food web dynamics and ecosystem functioning in these unique environments.

Characterization of hydrothermal fluids that alter the upper oceanic crust to spilite and epidosite: Fluid inclusion evidence from the Semail (Oman) and Troodos (Cyprus) ophiolites

Pervasive alteration of basaltic oceanic crust by heated seawater at greenschist facies conditions produces two contrasting hydrothermal rocks. “Spilites”, consisting of chlorite + albite + quartz ± actinolite ± epidote, occur typically with regional extents. Locally spilites are metasomatically transformed to “epidosites” consisting of epidote + quartz + titanite + hematite or magnetite. Both alteration types have been proposed as markers of deep hydrothermal upflow in sub-seafloor convection cells, and as sources of the ore metals in basalt-hosted seafloor massive sulfide deposits. Little direct evidence is available for the chemical compositions of these fluids in their states deep in the upflow zones prior to their discharge at the seafloor. To better characterize them we have conducted a field, petrographic and fluid inclusion study of the lavas, sheeted dikes and plagiogranites in the Semail ophiolite, with supporting samples from the Troodos ophiolite. Our results show that both the spilite- and epidosite-forming fluids were single-phase aqueous liquids during the hydrothermal alteration. At some sites their salinity is 3.1–3.2 wt.% NaCleq, which we take to represent the chlorinity of Cenomanian seawater in the Semail realm. At other sites salinities are as low as 2.4 wt.% NaCleq or as high as 5.7 wt.% NaCleq, attributable to liquid–vapor separation and partial remixing deep in the crust along the dew curve of seawater, prior to ascent of the fluids to the sites of fluid inclusion trapping. Hypersaline brines, often accompanied by vapor, are restricted to plagiogranites in both the Semail and Troodos ophiolites and they represent magmatic–hydrothermal fluids that pre-date and are genetically unrelated to the spilite and epidosite alteration. The volcanostratigraphic locations of the samples constrain their maximum depths to 1470–3600 m below seafloor during alteration. The range of possible fluid trapping pressures for all samples is 31–68 MPa. Trapping temperatures vary between sites from 145 to 440 °C for spilite fluids and 255 to 435 °C for epidosite fluids. Quantitative analyses of 12 elements in individual fluid inclusions by LA-ICP-MS define the chemical characters of the two alteration fluids. The Br/Cl ratio in the spilite fluid is the same as in modern seawater and the other elements fit expectations from seawater–basalt experiments at elevated temperature. Accordingly, concentrations of Li, B, Na, Cl, K, Br and Sr in the spilite fluid match those in modern black-smoker vent fluids in basaltic crust. Exceptions are Ca and Fe, which are enriched in the spilite fluid. As these elements may precipitate below or at the seafloor prior to vent sampling, we conclude that the spilite fluids are plausible feeders of basalt-hosted black-smoker vents. The epidosite fluid has broadly similar elemental concentrations to the spilite fluid, but vastly lower Fe, reflecting the highly oxidized state of epidosites. This suggests that epidosite fluids are incapabable of forming basalt-hosted seafloor massive sulfide deposits.

Exploring brain diversity in crustaceans: sensory systems of deep vent shrimps

Abstract The current report focuses on shrimps from deep hydrothermal vents of the Mid-Atlantic Ridge that live in an environment characterized by high hydrostatic pressure, lack of sunlight, and with hot and potentially toxic emissions of black smoker vents. Malacostracan crustaceans display a large diversity of lifestyles and life histories and a rich repertoire of complex behavioral patterns including sophisticated social interactions. These aspects promote this taxon as an interesting group of organisms for those neurobiologists interested in evolutionary transformation of brain structures and evolutionary diversification of neuronal circuits. Here, we explore how analyzing the nervous system of crustacean species from extreme habitats can provide deeper insights into the functional adaptations that drive the diversification of crustacean brain structure.

Geoelectrodes and Fuel Cells for Simulating Hydrothermal Vent Environments.

Gradients generated in hydrothermal systems provide a significant source of free energy for chemosynthetic life and may play a role in present-day habitability on ocean worlds. Electron/proton/ion gradients, particularly in the context of hydrothermal chimney structures, may also be relevant to the origins of life on Earth. Hydrothermal vents are similar in some ways to typical fuel cell devices: redox/pH gradients between seawater and hydrothermal fluid are analogous to the fuel cell oxidant and fuel reservoirs; the porous chimney wall is analogous to a separator or ion-exchange membrane and is also a conductive path for electrons; and the hydrothermal minerals are analogous to electrode catalysts. The modular and scalable characteristics of fuel cell systems make for a convenient planetary geology test bed in which geologically relevant components may be assembled and investigated in a controlled simulation environment. We have performed fuel cell experiments and electrochemical studies to better understand the catalytic potential of seafloor minerals and vent chimneys, using samples from a black smoker vent chimney as an initial demonstration. In a fuel cell with Na+-conducting Nafion® membranes and liquid fuel/oxidant reservoirs (simulating the vent environment), the black smoker mineral catalyst in the membrane electrode assembly was effective in reducing O2 and oxidizing sulfide. In a H2/O2 polymer electrolyte membrane (PEM) fuel cell with H+-conducting Nafion membranes, the black smoker catalyst was effective in reducing O2 but not in oxidizing H2. These fuel cell experiments accurately simulated the redox reactions that could occur in a geological setting with this particular catalyst, and also tested whether the minerals are sufficiently active to replace a commercial fuel cell catalyst. Similar experiments with other geocatalysts could be utilized to test which redox reactions could be driven in other hydrothermal systems, including hypothesized vent systems on other worlds.

Geochemistry of fluids from Earth’s deepest ridge-crest hot-springs: Piccard hydrothermal field, Mid-Cayman Rise

Hosted in basaltic substrate on the ultra-slow spreading Mid-Cayman Rise, the Piccard hydrothermal field is the deepest currently known seafloor hot-spring (4957–4987 m). Due to its great depth, the Piccard site is an excellent natural system for investigating the influence of extreme pressure on the formation of submarine vent fluids. To investigate the role of rock composition and deep circulation conditions on fluid chemistry, the abundance and isotopic composition of organic, inorganic, and dissolved volatile species in high temperature vent fluids at Piccard were examined in samples collected in 2012 and 2013.Fluids from the Beebe Vents and Beebe Woods black smokers vent at a maximum temperature of 398 °C at the seafloor, however several lines of evidence derived from inorganic chemistry (Cl, SiO2, Ca, Br, Fe, Cu, Mn) support fluid formation at much higher temperatures in the subsurface. These high temperatures, potentially in excess of 500 °C, are attainable due to the great depth of the system. Our data indicate that a single deep-rooted source fluid feeds high temperature vents across the entire Piccard field. High temperature Piccard fluid H2 abundances (19.9 mM) are even higher than those observed in many ultramafic-influenced systems, such as the Rainbow (16 mM) and the Von Damm hydrothermal fields (18.2 mM). In the case of Piccard, however, these extremely high H2 abundances can be generated from fluid-basalt reaction occurring at very high temperatures.Magmatic and thermogenic sources of carbon in the high temperature black smoker vents are described. Dissolved ΣCO2 is likely of magmatic origin, CH4 may originate from a combination of thermogenic sources and leaching of abiotic CH4 from mineral-hosted fluid inclusions, and CO abundances are at equilibrium with the water–gas shift reaction. Longer-chained n-alkanes (C2H6, C3H8, n-C4H10, i-C4H10) may derive from thermal alteration of dissolved and particulate organic carbon sourced from the original seawater source, entrainment of microbial ecosystems peripheral to high temperature venting, and/or abiotic mantle sources. Dissolved ΣHCOOH in the Beebe Woods fluid is consistent with thermodynamic equilibrium for abiotic production via ΣCO2 reduction with H2 at 354 °C measured temperature. A lack of ΣHCOOH in the relatively higher temperature 398 °C Beebe Vent fluids demonstrates the temperature sensitivity of this equilibrium.Abundant basaltic seafloor outcrops and the axial location of the vent field, along with multiple lines of geochemical evidence, support extremely high temperature fluid-rock reaction with mafic substrate as the dominant control on Piccard fluid chemistry. These results expand the known diversity of vent fluid composition, with implications for supporting microbiological life in both the modern and ancient ocean.

Boiling-induced formation of colloidal gold in black smoker hydrothermal fluids

Gold colloids occur in black smoker fluids from the Niua South hydrothermal vent field, Lau Basin (South Pacific Ocean), confirming the long-standing hypothesis that gold may undergo colloidal transport in hydrothermal fluids. Six black smoker vents, varying in temperature from 250 °C to 325 °C, were sampled; the 325 °C vent was boiling at the time of sampling and the 250 °C fluids were diffusely venting. Native gold particles ranging from <50 nm to 2 μm were identified in 4 of the fluid samples and were also observed to precipitate on the sampler during collection from the boiling vent. Total gold concentrations (dissolved and particulate) in the fluid samples range from 1.6 to 5.4 nM in the high-temperature, focused flow vents. Although the gold concentrations in the focused flow fluids are relatively high, they are lower than potential solubilities prior to boiling and indicate that precipitation was boiling induced, with sulfide lost upon boiling to exsolution and metal sulfide formation. Gold concentrations reach 26.7 nM in the 250 °C diffuse flow sample, and abundant native gold particles were also found in the fluids and associated sulfide chimney and are interpreted to be a product of colloid accumulation and growth following initial precipitation upon boiling. These results indicate that colloid-driven precipitation as a result of boiling, the persistence of colloids after boiling, and the accumulation of colloids in diffuse flow fluids are important mechanisms for the enrichment of gold in seafloor hydrothermal systems.

Archaea S-layer nanotube from a "black smoker" in complex with cyclo-octasulfur (S8 ) rings.

Elemental sulfur exists primarily as an S80 ring and serves as terminal electron acceptor for a variety of sulfur-fermenting bacteria. Hyperthermophilic archaea from black smoker vents are an exciting research tool to advance our knowledge of sulfur respiration under extreme conditions. Here, we use a hybrid method approach to demonstrate that the proteinaceous cavities of the S-layer nanotube of the hyperthermophilic archaeon Staphylothermus marinus act as a storage reservoir for cyclo-octasulfur S8. Fully atomistic molecular dynamics (MD) simulations were performed and the method of multiconfigurational thermodynamic integration was employed to compute the absolute free energy for transferring a ring of elemental sulfur S8 from an aqueous bath into the largest hydrophobic cavity of a fragment of archaeal tetrabrachion. Comparisons with earlier MD studies of the free energy of hydration as a function of water occupancy in the same cavity of archaeal tetrabrachion show that the sulfur ring is energetically favored over water.

Long-term, quantitative observations of seafloor hydrothermal venting using an imaging sonar

While connected to the NEPTUNE observatory operated by Ocean Networks Canada (ONC) at the Endeavour Segment of the Juan de Fuca Ridge (http://www.oceannetworks.ca/observatories/pacific), the Cabled Observatory Vent Imaging Sonar (COVIS) recorded an unprecedented long-term (&amp;gt;4 years) acoustic dataset capturing local hydrothermal venting. Processing of the acoustic backscatter data yields three-dimensional (3-D) images of plumes rising tens of meters from black smoker vents on a sulfide structure named Grotto. More importantly, analysis of the Doppler frequency shift in acoustic backscatter yields estimates of the flow rates of those plumes and their volume fluxes. Subsequent calculations based on the vertical variation in volume flux and a theoretical heat-to-volume-flux relationship for buoyancy-driven plumes give estimates of plume heat flux, which are essential for studying the temporal evolution of a hydrothermal system and its coupling with geological, oceanic, and biological processes. In addition to black-smoker plume observations, the ping-to-ping decorrelation of seafloor backscatter recorded by COVIS provides an acoustic indicator of diffuse-flow (i.e., low- temperature, clear hydrothermal discharge) distribution over Grotto and its surrounding areas. Furthermore, acoustic techniques for quantifying the temperature fluctuations, and ultimately, heat flux of diffuse-flow venting are currently under development. [Work supported by NSF.]

Cutting through the smoke: the diversity of microorganisms in deep-sea hydrothermal plumes.

There are still notable gaps regarding the detailed distribution of microorganisms between and within insular habitats such as deep-sea hydrothermal vents. This study investigates the community composition of black smoker vent microorganisms in the Southern Hemisphere, and changes thereof along a spatial and chemical gradient ranging from the vent plume to surrounding waters. We sampled two hydrothermal vent fields, one at the South West Indian Ridge (SWIR), the other at the East Scotia Ridge (ESR). Samples were collected across vent fields at varying vertical distances from the origin of the plumes. The microbial data were sequenced on an Illumina MiSeq platform for the 16SrRNA gene. A substantial amount of vent-specific putative chemosynthetic microorganisms were found, particularly in samples from focused hydrothermal venting. Common vent-specific organisms from both vent fields were the genera Arcobacter, Caminibacter and Sulfurimonas from the Epsilonproteobacteria and the SUP05 group from the Gammaproteobacteria. There were no major differences in microbial composition between SWIR and ESR for focused plume samples. However, within the ESR the diffuse flow and focused samples differed significantly in microbial community composition and relative abundance. For Epsilonproteobacteria, we found evidence of niche-specificity to hydrothermal vent environments. This taxon decreased in abundance by three orders of magnitude from the vent orifice to background water. Epsilonproteobacteria distribution followed a distance–decay relationship as vent-effluents mixed with the surrounding seawater. This study demonstrates strong habitat affinity of vent microorganisms on a metre scale with distinct environmental selection.

Subaqueous cryptodome eruption, hydrothermal activity and related seafloor morphologies on the andesitic North Su volcano

North Su is a double-peaked active andesite submarine volcano located in the eastern Manus Basin of the Bismarck Sea that reaches a depth of 1154m. It hosts a vigorous and varied hydrothermal system with black and white smoker vents along with several areas of diffuse venting and deposits of native sulfur. Geologic mapping based on ROV observations from 2006 and 2011 combined with morphologic features identified from repeated bathymetric surveys in 2002 and 2011 documents the emplacement of a volcanic cryptodome between 2006 and 2011. We use our observations and rock analyses to interpret an eruption scenario where highly viscous, crystal-rich andesitic magma erupted slowly into the water-saturated, gravel-dominated slope of North Su. An intense fragmentation process produced abundant blocky clasts of a heterogeneous magma (olivine crystals within a rhyolitic groundmass) that only rarely breached through the clastic cover onto the seafloor. Phreatic and phreatomagmatic explosions beneath the seafloor cause mixing of juvenile and pre-existing lithic clasts and produce a volcaniclastic deposit. This volcaniclastic deposit consists of blocky, non-altered clasts next, variably (1–100%) altered clasts, hydrothermal precipitates and crystal fragments. The usually applied parameters to identify juvenile subaqueous lava fragments, i.e. fluidal shape or chilled margin, were not applicable to distinguish between pre-existing non-altered clasts and juvenile clasts. This deposit is updomed during further injection of magma and mechanical disruption. Gas-propelled turbulent clast-recycling causes clasts to develop variably rounded shapes. An abundance of blocky clasts and the lack of clasts typical for the contact of liquid lava with water is interpreted to be the result of a cooled, high-viscosity, crystal-rich magma that failed as a brittle solid upon stress. The high viscosity allows the lava to form blocky and short lobes. The pervasive volcaniclastic cover on North Su is partly cemented by hydrothermal precipitates. These hydrothermally-cemented breccias, crusts and single pillars show that hydrothermal circulation through a thick layer of volcaniclastic deposits can temporarily increase slope stability through precipitation and cementation.

Microbial iron mats at the Mid-Atlantic Ridge and evidence that Zetaproteobacteria may be restricted to iron-oxidizing marine systems.

Chemolithoautotrophic iron-oxidizing bacteria play an essential role in the global iron cycle. Thus far, the majority of marine iron-oxidizing bacteria have been identified as Zetaproteobacteria, a novel class within the phylum Proteobacteria. Marine iron-oxidizing microbial communities have been found associated with volcanically active seamounts, crustal spreading centers, and coastal waters. However, little is known about the presence and diversity of iron-oxidizing communities at hydrothermal systems along the slow crustal spreading center of the Mid-Atlantic Ridge. From October to November 2012, samples were collected from rust-colored mats at three well-known hydrothermal vent systems on the Mid-Atlantic Ridge (Rainbow, Trans-Atlantic Geotraverse, and Snake Pit) using the ROV Jason II. The goal of these efforts was to determine if iron-oxidizing Zetaproteobacteria were present at sites proximal to black smoker vent fields. Small, diffuse flow venting areas with high iron(II) concentrations and rust-colored microbial mats were observed at all three sites proximal to black smoker chimneys. A novel, syringe-based precision sampler was used to collect discrete microbial iron mat samples at the three sites. The presence of Zetaproteobacteria was confirmed using a combination of 16S rRNA pyrosequencing and single-cell sorting, while light micros-copy revealed a variety of iron-oxyhydroxide structures, indicating that active iron-oxidizing communities exist along the Mid-Atlantic Ridge. Sequencing analysis suggests that these iron mats contain cosmopolitan representatives of Zetaproteobacteria, but also exhibit diversity that may be uncommon at other iron-rich marine sites studied to date. A meta-analysis of publically available data encompassing a variety of aquatic habitats indicates that Zetaproteobacteria are rare if an iron source is not readily available. This work adds to the growing understanding of Zetaproteobacteria ecology and suggests that this organism is likely locally restricted to iron-rich marine environments but may exhibit wide-scale geographic distribution, further underscoring the importance of Zetaproteobacteria in global iron cycling.

Rapid generation of reaction permeability in the roots of black smoker systems, Troodos ophiolite, Cyprus

AbstractThe deep levels of former black smoker hydrothermal systems are widespread in the Troodos ophiolite in Cyprus. They are marked by zones of hydrothermal reaction in the sheeted dyke unit close to the underlying gabbros. These zones are characterized by the presence of epidosite (epidote–quartz rock). In the reaction zones, the dykes are altered to a range of greenschist facies mineral assemblages, from a low degree of alteration with a five to seven phase metabasaltic assemblage to a high degree of alteration with a two to three phase epidosite assemblage. Individual dykes may contain the full range, with the epidosites forming yellow–green stripes within a darker background, often extending for more than several metres, parallel to the dyke margins. Field relations show that the alteration took place on a dyke‐by‐dyke basis and was not a regional process. SEM petrography reveals that the epidosites contain millimetre scale pores. The minerals surrounding the pores show euhedral overgrowths into the free pore space, indicating a former transient porosity of up to 20%. We conclude that the epidosites formed by reaction between newly intruded basaltic dykes and actively circulating black smoker fluid leading to extensive dissolution of primary dyke minerals. This reaction generated the porosity in the stripes and transiently led to a much increased permeability, allowing the rapid penetration of the black smoker fluid into the dykes and flow along them in fingers. As the system evolved, the same flow regime allowed mineral precipitation and partial infilling of the porosity. This mechanism allows rapid recrystallization of the rock with release of metals and other components into the fluid. This explains the depletion of these components in epidosites and their enrichment in black smoker vent fluids and the relatively constant composition of vent fluids as fresh rock is continually mined.

Geomorphological variations at hydrothermal sites in the southern Mariana Trough: Relationship between hydrothermal activity and topographic characteristics

This study presents the first detailed geomorphological characterization of field-scale geological features associated with hydrothermal systems in the southern Mariana Trough, using near-bottom swath mapping data collected by the autonomous underwater vehicle (AUV) Urashima during cruise YK09-08 and dive observation data acquired by the submersible Shinkai6500 during cruise YK10-11. The motivation of this study is to examine the relationship between geomorphological characteristics and hydrothermal activity, and to examine the nature of tectonic and volcanic controls on the hydrothermal system in this area. Two of the hydrothermal sites in the study area (near 12°57′N, 143°37′E) are located on the active backarc spreading axis (the Snail and Yamanaka sites), one is located at the eastern foot of the axial high (the Archean site), and two are located on an off-axis knoll about 5km from the spreading axis (the Pika and Urashima sites). The on-axis area is divided into tectonically dominant and volcanically dominant zones; volcanically dominant zones are characterized by mounds (height, 5–30m; diameter, 250–320m) cut by fissures. The Snail and Yamanaka sites are located adjacent to these fissures, and are possibly represented local activity associated with a 4th order segment-scale diking event (on the basis of comparisons with previously studied cases on the East Pacific Rise with similar on-axis geological characteristics). In contrast to the on-axis sites, the off-axis sites show no evidence of faulting. The Archean site at the foot of the axial high is characterized by a single mound (height, 50–100; diameter, 250–300m), pronounced off-axis lava flows, and the presence of high-amplitude rugged seafloor features; the site is located at the top of the mound. Numerous ridge lines (height, mainly 2–6m) extend radially from the top of the mound, and several chimney-like structures (up to approximately 6m high) occur on the top and slopes of the mound. The Pika site is located on the western peak of an off-axis knoll, and the newly discovered Urashima site is located at the northern foot of the western peak of the same knoll. The western peak is characterized by bumpy seabed textures formed by numerous smaller-scale mounds and ridge lines; however, the eastern peak has a very smooth top and slope, and shows no signs of hydrothermal activity. Numerous mounds (heights, 5–75m; diameters, 50–350m) are developed on the comparatively gentle slope of the knoll, in contrast to the numerous ridge lines (height, mainly 1–6m) developed on the relatively steep slopes of the knoll. On the basis of the associated geomorphological features, the three off-axis sites (Archean, Pika, and Urashima) were identified as localities created by relatively long-term large-scale hydrothermal activity, as compared with sites in the on-axis area. The sustained activity at off-axis sites appears closely related to an off-axis upwelling magma system. The three off-axis hydrothermal sites are composed mainly of breccia assemblages that probably originated from hydrothermal activity with black smoker venting. These areas are characterized by numerous ridge lines, conical mounds, and bumpy seabed texture, whereas the on-axis sites are characterized by the absence of ridge lines, and the presence of white smoker and shimmering observed on dome-shaped pillow mounds. Hence, the distribution of ridge lines, mound morphology, and bumpy seabed texture is likely to correlate with hydrothermal activity.

Nicomache (Loxochona) lokii sp. nov. (Annelida: Polychaeta: Maldanidae) from the Loki’s Castle vent field: an important structure builder in an Arctic vent system

The discovery of the Loki’s Castle vent field at 2,350 m depth on the Arctic mid-ocean ridge in 2008 represents the first known black smoker vent system in the Arctic region. Preliminary results on the benthic invertebrates collected at Loki’s Castle indicate the presence of an endemic fauna dominated by tube-building polychaetes, melitid amphipods and gastropods. Here, we formally describe and investigate the ecological role of a new maldanid species, Nicomache (Loxochona) lokii sp. nov., a species found to be particularly common and regarded as a keystone species in this vent system. The description of the new species is supplemented with a DNA barcode. The subgenus N. (Loxochona) includes at present six nominal species, and the new species described herein is the fourth species associated with reducing habitats. A table with diagnostic characters for all species referred to the subgenus is provided. The new species builds tubes up to a length of 20 cm or more, tightly fastened to the substratum. Together with other tube-building species, N. (L.) lokii sp. nov. form a complex three-dimensional habitat for a number of free-living invertebrates. Based on the morphology of the foregut, the microbial community in the gut and the stable isotope values found for this species, it is concluded that it acts as a grazer in this vent system.

Sonar images hydrothermal vents in seafloor observatory

Hydrothermal plumes venting from black smokers and diffuse flow discharging from the surrounding area of the seafloor are important as agents of transfer of heat, chemicals, and biological material from the crust into the ocean in quantitatively significant amounts [Elderfield and Schultz, 1996]. An unprecedented time series of three‐dimensional (3‐D) volume images of plumes rising tens of meters from black smoker vents and of concurrent 2‐D maps of diffuse flow discharging from surrounding areas of the seafloor illuminates the turbulent behavior of hydrothermal fluid transfer into the ocean (seeFigure 1).

Direct observation of a fossil high-temperature, fault-hosted, hydrothermal upflow zone in crust formed at the East Pacific Rise

Fault zones in the ocean crust are commonly hypothesized to act as high-permeability conduits that focus fl uid fl ow in oceanic hydrothermal systems. However, there has been little direct study of faults in crust formed at fast-spreading ridges. Here we describe the geology and geochemistry of an ~40-m-wide fault zone within the uppermost sheeted dike complex exposed at Pito Deep (northeastern Easter microplate). Titanium in quartz thermometry gives temperatures of 392 ± 33 °C for quartz precipitation, indicating that this fault zone focused upwelling fl uids at temperatures similar to those of black-smoker vent fl uids. Correlated enrichment in 87 Sr/ 86 Sr and MgO in fault breccias, along with 87 Sr/ 86 Sr ratios higher than in average vent fl uids, provide evidence for mixing between high-temperature upwelling fl uids and a seawater-like fl uid within the fault zone. Large high-temperature fl uid fl uxes are required to maintain high temperatures during mixing. If this fault zone is representative of upfl ow zones beneath hydrothermal vents on the East Pacifi c Rise, then it is possible that vent fl uids evolve thermally and chemically during their ascent and may not record the precise conditions at the base of the hydrothermal system.

Flow rate perturbations in a black smoker hydrothermal vent in response to a mid‐ocean ridge earthquake swarm

Although there is indirect evidence for strong connections between tectonic processes and mid‐ocean ridge hydrothermal flow, there are no direct observations of these links, primarily because measuring flow in these systems is difficult. Here we use an optical analysis technique to obtain a 44 day record of flow rate changes in a black smoker vent in the Main Endeavour field of the Juan de Fuca Ridge. We show that variations in the flow rate coincide with an earthquake swarm observed using an ocean bottom seismometer array. These observations indicate that connections between tectonics and flow are indeed strong, that hydraulic connections within this hydrothermal system are long ranging, and that enhanced tidal pumping of fluids may be initiated by earthquake activity. Because the effects of the swarm cross over an intervening vent field, we infer that the upflow zones feeding this field are narrow. Using the time lag between the swarm onset and the flow rate changes we estimate that the bulk permeability of the crust on the Endeavour segment ranges from 3.0 × 10−13 m2 to 6.0 × 10−12 m2.

Metals in deep liquid of the Reykjanes geothermal system, southwest Iceland: Implications for the composition of seafloor black smoker fluids

Seafloor hydrothermal systems precipitate Cu, Zn, and Fe sulfides at and below black smoker vents on the seafloor; as a result, the metal concentrations in the vent fluids are minimum values. We sampled deep, unboiled liquids from the Reykjanes geothermal reservoir, Iceland, and measured the metal concentrations. This active, seawater-dominated system, situated on the Mid-Atlantic Ridge, is the subaerial equivalent to mid-ocean-ridge hydro thermal systems. The liquids, collected at 1350–1500 m depth and 284–295 °C, contain 154–2431 μ M Fe (9–140 ppm), 207–261 μ M Cu (14–17 ppm), 79–393 μ M Zn (5–27 ppm), 0.6–1.4 μ M Pb (120–290 ppb), 6–31 n M Au (1–6 ppb), and 250–960 n M Ag (28–107 ppb). Fluids discharged at surface from the same wells have orders of magnitude lower metal concentrations due to precipitation caused by boiling and vapor loss during depressurization. The concentrations of Cu, Zn, and Pb in the high-temperature reservoir liquids at Reykjanes are similar to those in the highest-temperature black smoker discharges, whereas Au and Ag concentrations are one to two orders of magnitude higher at Reykjanes; lower-temperature seafloor fluids have lower metal contents, suggesting subseafloor deposition before discharge. The Reykjanes heat flux of 130 MW requires a liquid flux of ~100 kg/s; over 104 yr, the minimum life of the system, 0.5 Mt each of Cu and Zn may have precipitated at depth.

The role of magma injection in localizing black-smoker activity

The mechanisms for localization of black-smoker systems at mid-ocean ridges remain to be fully understood. Seismic data for a segment of the Juan de Fuca ridge with long-lived black-smoker vents reveal ongoing magma recharge into the crustal magma chamber, thereby providing an explanation for the localization.

First evidence for high-temperature off-axis venting of deep crustal/mantle heat: The Nibelungen hydrothermal field, southern Mid-Atlantic Ridge

During segment-scale studies of the southern Mid-Atlantic Ridge (MAR), 7–12° S, we found evidence in the water column for high-temperature hydrothermal activity, off-axis, east of Ascension Island. Extensive water column and seafloor work using both standard CTD and deep submergence AUV and ROV deployments led to the discovery and sampling of the “Drachenschlund” (“Dragon Throat”) black smoker vent at 8°17.87′ S/13°30.45′ W in 2915 m water depth. The vent is flanked by several inactive chimney structures in a field we have named “Nibelungen”. The site is located 6 km south of a non-transform offset between two adjacent 2nd-order ridge-segments and 9 km east of the presently-active, northward-propagating A2 ridge-segment, on a prominent outward-facing fault scarp. Both vent-fluid compositions and host-rock analyses show this site to be an ultramafic-hosted system, the first of its kind to be found on the southern MAR. The thermal output of this single vent, based on plume rise-height information, is estimated to be 60 ± 15 MW. This value is high for a single “black smoker” vent but small for an entire field. The tectonic setting and low He content of the vent fluids imply that high-temperature off-axis venting at “Drachenschlund” is driven not by magmatic processes, as at the majority of on-axis hydrothermal systems, but by residual heat “mined” from the deeper lithosphere. Whether this heat is being extracted from high-temperature mantle peridotites or deep crustal cumulates formed at the “duelling” non-transfrom offset is unclear, in either case the Drachenschlund vent provides the first direct observations of how cooling of deeper parts of the lithosphere, at least at slow-spreading ridges, may be occurring.