Submarine Hot Springs Research Articles

Submarine hot spring discharges along the coast of Beppu Bay as observed by radon towing survey

Submarine hot spring discharges along the coast of Beppu Bay as observed by radon towing survey

Great Mining Camps of Canada 7. The Bathurst Mining Camp, New Brunswick, Part 1: Geology and Exploration History

The Bathurst Mining Camp of northern New Brunswick is approximately 3800 km2 in area, encompassed by a circle of radius 35 km. It is known worldwide for its volcanogenic massive sulphide deposits, especially for the Brunswick No. 12 Mine, which was in production from 1964 to 2013. The camp was born in October of 1952, with the discovery of the Brunswick No. 6 deposit, and this sparked a staking rush with more hectares claimed in the province than at any time since. In 1952, little was known about the geology of the Bathurst Mining Camp or the depositional settings of its mineral deposits, because access was poor and the area was largely forest covered. We have learned a lot since that time. The camp was glaciated during the last ice age and various ice-flow directions are reflected on the physiographic map of the area. Despite abundant glacial deposits, we now know that the camp comprises several groups of Ordovician predominantly volcanic rocks, belonging to the Dunnage Zone, which overlie older sedimentary rocks belonging to the Gander Zone. The volcanic rocks formed during rifting of a submarine volcanic arc on the continental margin of Ganderia, ultimately leading to the formation of a Sea of Japan-style basin that is referred to as the Tetagouche-Exploits back-arc basin. The massive sulphide deposits are mostly associated with early-stage, felsic volcanic rocks and formed during the Middle Ordovician upon or near the sea floor by precipitation from metalliferous fluids escaping from submarine hot springs. The history of mineral exploration in the Bathurst Mining Camp can be divided into six periods: a) pre-1952, b) 1952-1958, c) 1959-1973, d) 1974-1988, and e) 1989-2000, over which time 45 massive sulphide deposits were discovered. Prior to 1952, only one deposit was known, but the efforts of three men, Patrick (Paddy) W. Meahan, Dr. William J. Wright, and Dr. Graham S. MacKenzie, focused attention on the mineral potential of northern New Brunswick, which led to the discovery of the Brunswick No. 6 deposit in October 1952. In the 1950s, 29 deposits were discovered, largely resulting from the application of airborne surveys, followed by ground geophysical methods. From 1959 to 1973, six deposits were discovered, mostly satellite bodies to known deposits. From 1974 to 1988, five deposits were found, largely because of the application of new low-cost analytical and geophysical techniques. From 1989 to 2000, four more deposits were discovered; three were deep drilling targets but one was at surface.

Prospecting for life.

Books with titles like 'The Call of the Wild' seemed to set a path for a life. Thus, I would be an explorer-a plan that did not work out so well, at least at first. On leaving school I got a job as a 'Works Chemist Improver', testing Ni catalysts for the hydrogenation of phenol to cyclohexanol. Taking night classes I passed enough exams to study geology at Queen Mary College, London. Armed thus I travelled to the Solomon Islands where geology is a 'happening'! Next was Canada to visit a mine sunk into a 1.5 billion year old Pb-Zn orebody precipitated from submarine hot springs. At last I reached the Yukon to prospect for silver. Thence to Ireland researching what I also took to be 'exhalative' (i.e. hot spring-related) Pb-Zn orebodies. While there in 1979, the discovery of 350°C metal-bearing acidic waters issuing from submarine Black Smoker chimneys in the Pacific sent us searching for fossil examples in the Irish mines. However, the chimneys we found were more like chemical gardens than Black Smokers, a finding that made us think about the emergence of life. After all, what better for life's emergence than to have a membrane comprising Fe minerals dosed with Ni in our chimneys to mediate the 'hydrogenation' of CO2-life's job anyway. Indeed, such a membrane would keep redox and pH disequilibria at bay, just like biological membranes. At the same time, my field research among Alpine ophiolites-ocean floor mafic rocks obducted to the Alps-indicated that alkaline waters bearing H2 and CH4 were a result of serpentinization, a process that must have operated in all ocean floors over all time. Thus it was that we could predict the Lost City hydrothermal field 10 years before its discovery in the North Atlantic in the year 2000. Lost City comprises a number of alkaline springs at up to 90°C that produce carbonate and brucite (Mg[OH]2) chimneys. We had surmised that Ni-enriched FeS chimneys would have precipitated at comparable alkaline springs issuing into a metal-rich carbonic ocean on the very early Earth (inducing membrane potentials comparable to those capable of succouring all life, and presumably, sufficient to drive life into being). However, our laboratory precipitates also revealed green rust, thought to be the precursor to the magnetite now comprising the Archaean Banded Iron Formations. We now look upon green rust, also known as fougèrite, as the tangible, base fractal of life.

Recent Mn-Ag deposits in coastal hydrothermal springs in the Baja California Peninsula, Mexico

Hot springs with associated Mn-Ag mineralization were identified in the intertidal zone of the Bahia Concepcion Bay of the central-eastern Baja California Peninsula. Hot spring activity is related to a system of NW-SE faults that are associated with the opening of the Gulf of California. The hot springs are hosted by Miocene volcanic and volcaniclastic units of the Comondu Group. The maximum discharge temperature recorded is 72 °C, with the pH ranging from 6.2 to 6.5 and salinity values reaching up to 27 g/kg. Veins, stockworks, breccias, crusts, and organosedimentary stromatolites of silica-carbonate and Mn oxides are associated with the hot springs. The Mn oxide and silica deposits show an association with Ag, As, Ba, Ca, Cu, Mg, Pb, Sb, Sr, Tl, V, W, and Zn. Acanthite and native silver occur along with pyrite in a mineral assemblage rich in opal-A, todorokite, romanechite, aragonite, high-Mg calcite, and barite. Three distinct mineral associations characterized by sulfides, sulfates, and oxides are recognized. The silver minerals formed late in the paragenesis. Textural evidence suggests a microbial mediation for the Mn mineral deposition. Pourbaix diagrams for Mn and Ag species were constructed for the physicochemical conditions of the coastal hot springs. These diagrams show that both Mn and Ag minerals are stable at low temperature (65 °C), and near neutral pH, under slightly reducing or oxidizing conditions. The characteristics of the subaerial to shallow submarine hot springs and the results of the geochemical modeling suggest that the hydrothermal system in the Bahia Conception Bay is formed through convection of meteoric waters, intermixed with some saline fluids or seawater.

Formation of gas discharging from Taketomi submarine hot spring off Ishigaki Island in the southern Ryukyu Islands, Japan

Taketomi submarine hot spring lies off Ishigaki Island in the southern Ryukyu Islands and vents hot spring waters at temperatures up to ~50°C from the seafloor at a depth of 20m. We investigated the chemical and isotopic composition of gases discharging from Taketomi hot spring. The gases were composed mainly of methane, with secondary nitrogen at higher than atmospheric concentration. Carbon and hydrogen isotope data suggest that the methane in the discharging gases was derived mainly from thermal decomposition of organic matter. Helium isotopes were enriched in 3He relative to the atmosphere, suggesting a supply of mantle-derived helium to the discharging gases. The mantle-derived gases transfer the deep-originated thermal energy to the hot spring and thermogenesis of organic matter. The hydrocarbons in the venting gas could be sourced from sedimentary rocks of the Yaeyama or Shimajiri Groups, or Yaeyama metamorphic rocks, and added to the ascending gases as they pass through those source rocks on their way to the surface. Because the Pleistocene rocks of the Ryukyu Group beneath the hot spring have been altered by the spring activity, the Taketomi hot spring began venting after the Pleistocene.

Identification of sulfur sources and isotopic equilibria in submarine hot-springs using multiple sulfur isotopes

Multiple sulfur isotopes were measured in metal sulfide deposits, elemental sulfur, and aqueous hydrogen sulfide to constrain sulfur sources and the isotopic systematics of precipitation in seafloor hydrothermal vents. Areas studied include the Eastern Manus Basin and Lau Basin back-arc spreading centers and the unsedimented basalt-hosted Southern East Pacific Rise (SEPR) and sediment-hosted Guaymas Basin mid-ocean ridge spreading centers. Chalcopyrite and dissolved hydrogen sulfide (H2S) δ34S values range from −5.5‰ to +5.6‰ in Manus Basin samples, +2.4‰ to +6.1‰ in Lau Basin samples, and +3.7‰ to +5.7‰ in SEPR samples. Values of δ34S for cubic cubanite and H2S range from −1.4‰ to +4.7‰ in Guaymas Basin samples.Multiple sulfur isotope systematics in fluid-mineral pairs from the SEPR and Lau Basin show that crustal host rock and thermochemical reduction of seawater-derived dissolved sulfate (SO4) are the primary sources of sulfur in mid-ocean ridge and some back-arc systems. At PACMANUS and SuSu Knolls hydrothermal systems in the Eastern Manus Basin, a significant contribution of sulfur is derived from disproportionation of magmatic sulfur dioxide (SO2), while the remaining sulfur is derived from crustal host rocks and SO4 reduction. At the sedimented Guaymas Basin hydrothermal system, sulfur sources include crustal host rock, reduced seawater SO4, and biogenic sulfide. Vent fluid flow through fresher, less-mature sediment supplies an increased quantity of reactant organic compounds that may reduce 34S-enriched SO4, while fluid interaction with more highly-altered sediments results in H2S characterized by a small, but isotopically-significant input of 34S-depleted biogenic sulfides.Near-zero Δ33S values in all samples implicate the abiotic processes of SO4 reduction and leaching of host rock as the major contributors to sulfur content at a high temperature unsedimented mid-ocean ridge and at a back-arc system. Δ33S values indicate that SO2 disproportionation is an additional process that contributes sulfur to a different back-arc system and to acid spring-type hydrothermal fluid circulation. At the sedimented Guaymus Basin, near-zero Δ33S values are also observed, despite negative δ34S values that indicate inputs of biogenic pyrite for some samples.In contrast with previous studies reporting isotope disequilibrium between H2S and chalcopyrite, the δ34S values of chalcopyrite sampled from the inner 1–2mm of a chimney wall are within ±1‰ of δ34S values for H2S in the paired vent fluid, suggesting equilibrium fluid-mineral sulfur isotope exchange at 300–400°C. Isotopic equilibrium between hydrothermal fluid H2S and precipitating chalcopyrite implies that sulfur isotopes in the chalcopyrite lining across a chimney wall may accurately record past hydrothermal activity.

Isolation and Characterization of a Thermophilic, Obligately Anaerobic and Heterotrophic Marine <i>Chloroflexi</i> Bacterium from a <i>Chloroflexi</i>-dominated Microbial Community Associated with a Japanese Shallow Hydrothermal System, and Proposal for <i>Thermomarinilinea lacunofontalis</i> gen. nov., sp. nov.

A novel marine thermophilic and heterotrophic Anaerolineae bacterium in the phylum Chloroflexi, strain SW7T, was isolated from an in situ colonization system deployed in the main hydrothermal vent of the Taketomi submarine hot spring field located on the southern part of Yaeyama Archipelago, Japan. The microbial community associated with the hydrothermal vent was predominated by thermophilic heterotrophs such as Thermococcaceae and Anaerolineae, and the next dominant population was thermophilic sulfur oxidizers. Both aerobic and anaerobic hydrogenotrophs including methanogens were detected as minor populations. During the culture-dependent viable count analysis in this study, an Anaerolineae strain SW7T was isolated from an enrichment culture at a high dilution rate. Strain SW7T was an obligately anaerobic heterotroph that grew with fermentation and had non-motile thin rods 3.5–16.5 μm in length and 0.2 μm in width constituting multicellular filaments. Growth was observed between 37–65°C (optimum 60°C), pH 5.5–7.3 (optimum pH 6.0), and 0.5–3.5% (w/v) NaCl concentration (optimum 1.0%). Based on the physiological and phylogenetic features of a new isolate, we propose a new species representing a novel genus Thermomarinilinea: the type strain of Thermomarinilinea lacunofontalis sp. nov., is SW7T (=JCM15506T=KCTC5908T).

Iron-Sulfide-Bearing Chimneys as Potential Catalytic Energy Traps at Life's Emergence

The concept that life emerged where alkaline hydrogen-bearing submarine hot springs exhaled into the most ancient acidulous ocean was used as a working hypothesis to investigate the nature of precipitate membranes. Alkaline solutions at 25-70°C and pH between 8 and 12, bearing HS(-)±silicate, were injected slowly into visi-jars containing ferrous chloride to partially simulate the early ocean on this or any other wet and icy, geologically active rocky world. Dependent on pH and sulfide content, fine tubular chimneys and geodal bubbles were generated with semipermeable walls 4-100 μm thick that comprised radial platelets of nanometric mackinawite [FeS]±ferrous hydroxide [∼Fe(OH)(2)], accompanied by silica and, at the higher temperature, greigite [Fe(3)S(4)]. Within the chimney walls, these platelets define a myriad of micropores. The interior walls of the chimneys host iron sulfide framboids, while, in cases where the alkaline solution has a pH>11 or relatively low sulfide content, their exteriors exhibit radial flanges with a spacing of ∼4 μm that comprise microdendrites of ferrous hydroxide. We speculate that this pattern results from outward and inward radial flow through the chimney walls. The outer Fe(OH)(2) flanges perhaps precipitate where the highly alkaline flow meets the ambient ferrous iron-bearing fluid, while the intervening troughs signal where the acidulous iron-bearing solutions could gain access to the sulfidic and alkaline interior of the chimneys, thereby leading to the precipitation of the framboids. Addition of soluble pentameric peptides enhances membrane durability and accentuates the crenulations on the chimney exteriors. These dynamic patterns may have implications for acid-base catalysis and the natural proton motive force acting through the matrix of the porous inorganic membrane. Thus, within such membranes, steep redox and pH gradients would bear across the nanometric platelets and separate the two counter-flowing solutions, a condition that may have led to the onset of an autotrophic metabolism through the reduction of carbon dioxide.

Shallow submarine and subaerial, low-enthalpy hydrothermal manifestations in Punta Banda, Baja California, Mexico: Geophysical and geochemical characterization

The low-enthalpy geothermal system at Punta Banda (NW Baja California Peninsula, Mexico) has been studied because it might provide heat to future desalination plants in the city of Ensenada. Utilization of subaerial, intertidal and submarine hot springs is evaluated based on geochemical and geophysical data. The results of the geochemical studies show that the geothermal fluids have a major meteoric water component because seawater is not present at the subaerial springs and hot wells. The highest estimated reservoir temperature (140 °C) calculated using a silica geothermometer corresponds to the Agua Caliente intertidal manifestation, a promising area also identified by geophysics. Geothermometric calculations applied to the computed composition of the thermal end member yield a reservoir temperature of 137 °C. Cl/B ratios indicate that the thermal fluids discharged by the intertidal vents and subaerial springs are similar, but they differ from those of submarine vents. Geoelectrical models depict an anomalous conductive trend from the La Jolla well to the Agua Caliente manifestation, suggesting the presence of a fault that allows upflow of hot water from depth. Lastly, integration of geochemical and geophysical data identified the best site for future exploration drilling at Punta Banda.

A microfluidic in situ analyzer for ATP quantification in ocean environments

We have developed and tested a functionally integrated in situ analyzer, the IISA-ATP system, for microbial activity assays based on a quantitative determination of the total (particulate and dissolved) ATP in ocean environments. The IISA-ATP utilizes a PDMS-glass hybrid microfluidic device as its core functional element, which can perform cell lysis and total ATP quantification by a luciferin-luciferase bioluminescence assay in situ. Transparent heaters and a temperature sensor fabricated on a glass substrate provide temperature control. As a result of the evaluation using the microfluidic device with ATP standard solutions, the bioluminescence intensity was linearly correlated with 2 × 10(-12) to 2 × 10(-8) M of ATP. A detection limit of 1.1 × 10(-11) M was determined using the completed IISA-ATP system, which includes a miniature pumping module and a control module. As a result of the evaluation using the environmental seawater sample collected from Tokyo Bay, Japan, 2.7 × 10(-10) M of total ATP was successfully determined in the laboratory by the IISA-ATP. The system was operated at a shallow submarine hot spring area in Okinawa, Japan for an in situ trial. The result shows the system was successfully operated in situ and the total ATP was determined to be 3.4 × 10(-10) M.

Chemistry of hot springs along the Eastern Lau Spreading Center

The Eastern Lau Spreading Center (ELSC) is the southernmost part of the back-arc spreading axis in the Lau Basin, west of the Tonga trench and the active Tofua volcanic arc. Over its 397-km length it exhibits large and systematic changes in spreading rate, magmatic/tectonic processes, and proximity to the volcanic arc. In 2005, we collected 81 samples of vent water from six hydrothermal fields along the ELSC. The chemistry of these waters varies both within and between vent fields, in response to changes in substrate composition, temperature and pressure, pH, water/rock ratio, and input from magmatic gases and subducted sediment. Hot-spring temperatures range from 229° to 363 °C at the five northernmost fields, with a general decrease to the south that is reversed at the Mariner field. The southernmost field, Vai Lili, emitted water at up to 334 °C in 1989 but had a maximum venting temperature of only 121 °C in 2005, due to waning activity and admixture of bottom seawater into the subseafloor plumbing system. Chloride varies both within fields and from one field to another, from a low of 528 mmol/kg to a high of 656 mmol/kg, and may be enriched by phase separation and/or leaching of Cl from the rock. Concentrations of the soluble elements K, Rb, Cs, and B likewise increase southward as the volcanic substrate becomes more silica-rich, especially on the Valu Fa Ridge. Iodine and δ 7Li increase southward, and δ 11B decreases as B increases, apparently in response to increased input from subducted sediment as the arc is approached. Species that decrease southward as temperature falls are Si, H 2S, Li, Na/Cl, Fe, Mn, and 87Sr/ 86Sr, whereas pH, alkalinity, Ca, and Sr increase. Oxygen isotopes indicate a higher water/rock ratio in the three systems on Valu Fa Ridge, consistent with higher porosity in more felsic volcanic rocks. Vent waters at the Mariner vent field on the Valu Fa Ridge are significantly hotter, more acid and metal-rich, less saline, and richer in dissolved gases and other volatiles, including H 2S, CO 2, and F, than the other vent fields, consistent with input of magmatic gases. The large variations in geologic and geophysical parameters produced by back-arc spreading along the ELSC, which exceed those along mid-ocean ridge spreading axes, produce similar large variations in the composition of vent waters, and thus provide new insights into the processes that control the chemistry of submarine hot springs.

Kosmotoga arenicorallina sp. nov. a thermophilic and obligately anaerobic heterotroph isolated from a shallow hydrothermal system occurring within a coral reef, southern part of the Yaeyama Archipelago, Japan, reclassification of Thermococcoides shengliensis as Kosmotoga shengliensis comb. nov., and emended description of the genus Kosmotoga

A novel thermophilic and sulfur-reducing bacterium, strain S304(T), was isolated from the Taketomi submarine hot spring shallow hydrothermal field located at southern part of the Yaeyama Archipelago, Japan. The cells were non-motile short thick rods or oval cocci 1.1-2.7 μm in length and 1.1-1.9 μm in width. Strain S304(T) was an obligately anaerobic heterotroph and sulfur reduction stimulates growth. Growth was observed between 50-65°C (optimum 60°C), pH 6.2-8.0 (optimum pH 7.1), 1.0-6.0% NaCl concentration (optimum 3.0%). The fatty acid composition was C(16:0) (71.4%), C(18:0) (20.9%) and C(18:1) (7.7%). The G + C content of genomic DNA was 40.8 mol%. The 16S rRNA gene sequence analysis indicated that strain S304(T) belonged to the genus Kosmotoga. Based on physiological and phylogenetic features of a new isolate, we propose new species in the genus Kosmotoga: the type strain of Kosmotoga arenicorallina sp. nov is S304(T) (=JCM 15790(T) = DSM22549(T)). Thermococcoides shengliensis 2SM-2(T) is phylogenetically associated with Kosmotoga olearia 14.5.1(T). Based on the phylogenetic relationship between Thermococcoides shengliensis 2SM-2(T) and Kosmotoga olearia 14.5.1(T), we propose the reclassification of Thermococcoides shengliensis as Kosmotoga shengliensis comb. nov. (type strain 2SM-2(T)). In addition, an emended description of the genus Kosmotoga is proposed.

A novel trigger-based method for hydrothermal vents prospecting using an autonomous underwater robot

In this paper we address the problem of localizing active hydrothermal vents on the seafloor using an Autonomous Underwater Vehicle (AUV). The plumes emitted by hydrothermal vents are the result of thermal and chemical inputs from submarine hot spring systems into the overlying ocean. The Woods Hole Oceanographic Institution’s Autonomous Benthic Explorer (ABE) AUV has successfully localized previously undiscovered hydrothermal vent fields in several recent vent prospecting expeditions. These expeditions utilized the AUV for a three-stage, nested survey strategy approach (German et al. in Deep Sea Res. I 55:203–219, 2008). Each stage consists of a survey flown at successively deeper depths through easier to detect but spatially more constrained vent fluids. Ideally this sequence of surveys culminates in photographic evidence of the vent fields themselves. In this work we introduce a new adaptive strategy for an AUV’s movement during the first, highest-altitude survey: the AUV initially moves along pre-designed tracklines but certain conditions can trigger an adaptive movement that is likely to acquire additional high value data for vent localization. The trigger threshold is changed during the mission, adapting the method to the different survey profiles the robot may find. The proposed algorithm is vetted on data from previous ABE missions and measures of efficiency presented.

Periodic Behavior of the Bubble Jet (Geyser) in the Taketomi Submarine Hot Springs of the Southern Part of Yaeyama Archipelago, Japan

AbstractThe periodicity of the bubble jet that spouts intermittently from the Taketomi submarine hot spring in Yaeyama archipelago, Japan, was measured for the first time using an acoustic current meter. The time series analysis of the upward velocity for the data, without a spiky signal, indicates that the cycle fluctuates between 38 and 85 s. Focusing on the period of high and low tide, the dominant time cycles were 66 and 41 s, respectively. These results show that the fluctuation of pressure with tide affected the eruption period of the bubble jet. In accordance with the vertical tube theory, estimations of thermal source and recharge water temperatures were carried out by taking into account the boiling point change due to the tidal variation in hydrostatic pressure. The result indicated that if the heat source temperature was higher than 200.0 °C and recharge water temperature was preheated to 117.96 °C, the observed eruption time cycles at high and low tide were stable.

Marinamoeba thermophila, a new marine heterolobosean amoeba growing at 50 °C

Two amoeba strains were isolated from marine sediment taken at the same place with 18 months interval from a region of the sea floor heated by extended submarine hot springs and fumaroles. These thermophilic amoebae grow at temperatures up to 50 °C. Sequences of the internal transcribed spacer demonstrated that the two strains belong to the same species and are different from any genus for which sequences are known. Phylogeny using small subunit ribosomal RNA places the amoeba in the Heterolobosea. Their closest relatives are the hypersaline flagellate Pleurostomum flabellatum and the hypersaline amoeba Tulamoeba peronaphora. The freshwater amoeboflagellate genera Naegleria and Willaertia belong to the same phylogenetic clade in the Vahlkampfiidae. The new marine species does not transform into flagellates. It forms cysts, which are round to ellipsoidal with few pores. Because of their unique place in the molecular phylogenetic tree, and because there is no morphologically identical species found in the literature, these isolates are considered to be a new species and a new genus, Marinamoeba thermophila.

Geology, ore deposits and hydrothermal venting in Bahía Concepción, Baja California Sur, Mexico

Abstract Bahía Concepción is located in the eastern coast of the Baja California peninsula and it is shaped by northwestern–southeastern normal faults. These are associated with a 12–6 Ma rifting episode, although some have been reactivated since the Pliocene. The most abundant rocks correspond to the arc related Comondú Group, Oligocene to Miocene, which forms a mainly calc‐alkaline volcanic and volcaniclastic sequence. There are less extensive outcrops of sedimentary rocks, lava flows, domes and pyroclastic rocks of Pliocene to Quaternary ages. The Neogene volcanism in the area indicates a shift from a subduction regime to an intraplate volcanism related to continental extension and the opening of an oceanic basin. The Bahía Concepción area contains numerous Mn ore deposits, being the biggest at El Gavilán and Guadalupe. The Mn deposits occur as veins, breccias and stockworks, and are composed by Mn oxides (pyrolusite, coronadite, romanechite), dolomite, quartz and barite. The deposits are hosted in volcanic rocks of the Comondú Group and, locally, in Pliocene sedimentary rocks. Thus, the Mn deposits formed between the Middle Miocene and the Pliocene. The mineralized structures are associated with Miocene northwestern–southeastern fault systems, which are analogous to those associated with the Cu‐Co‐Zn‐Mn deposits of El Boleo. The Bahía Concepción area also bears subaerial and submarine hot springs, which are associated with the same fault systems and host rocks. The submarine and subaerial geothermal manifestations south of the bay are possibly related with recent volcanism. The geothermal manifestations within the bay are intertidal hot springs and shallow submarine diffuse venting areas. Around the submarine vents (5–15 m deep, 87°C), Fe‐oxyhydroxide crusts with pyrite and cinnabar precipitate. In the intertidal vents (62°C), aggregates of opal, calcite, barite and Ba‐rich Mn oxides occur covered by silica‐carbonate stromatolitic sinters. Some 10–30 cm thick crustiform veins formed by chalcedony, calcite and barite are also found close to the vents. The hydrothermal fluids exhibit mixed isotopic compositions between δ18O‐enriched meteoric and local marine water. The precipitation of Ba‐rich Mn oxides around the vent sites could be an active analog for the processes that produced Miocene to Pliocene hydrothermal Mn‐deposits.

Distribution, speciation and bioavailability of arsenic in a shallow-water submarine hydrothermal system, Tutum Bay, Ambitle Island, PNG

Shallow-water hydrothermal vent systems can introduce large amounts of potentially toxic elements, such as arsenic (As), into coastal marine environments. The first step in understanding and describing the potential impact of these elements throughout hydrothermally influenced coastal ecosystems is to determine the element's distribution and speciation, which in turn influences the availability of the toxin for biological uptake. Shallow submarine hot springs near Ambitle Island, Papua New Guinea, are discharging as much as 1.5 kg per day of arsenic directly into a coral-reef ecosystem. We have investigated the bioavailability of the As throughout Tutum Bay by studying vent fluid, seawater, pore water, precipitates, and sediments. In addition to measuring As abundance, As speciation (As(III), As(V), and the methylated species DMA and MMA) was determined in various waters. The As concentration for discrete mineral phases in vent precipitates and sediments was determined by sequentially extracting arsenic from the easily extractable, carbonate, Fe-oxyhydroxide or hydrous ferric oxide (HFO), and residual fractions, each of which have a different bioavailability. Diffuse venting seems to play a critical role on the distribution of As throughout Tutum Bay surface sediments, which have a mean As concentration of 527 ppm while excluding the vent precipitates (range = 1483 to 52 ppm). Up to 54 ppm As were extracted from the easily extractable fraction of surface sediments (mean = 19.7 ppm), using a K 2HPO 4/KH 2PO 4 buffer at pH = 7.2. Arsenic from this fraction is considered to be the most available for biological processes, and therefore the most dangerous for biota. However, sequential extraction shows that 98.6% of the As in vent precipitates, and a mean of 93.3% in surface sediments (range = 88.2% to 96.3%), is coprecipitated with the hydrous ferric oxide (HFO) fraction. Thus, the bulk of the As being discharged into Tutum Bay is scavenged by the HFO, and should remain stable unless the physicochemical conditions surrounding the oxides change. In surface seawaters of Tutum bay, we found as much as four times the average seawater concentration of As (8.4 μg/L compared to ∼2 μg/L). The abundance of As in seawater just above the sediment/water interface is near normal, although As(III) in both surface and bottom seawater throughout Tutum Bay is substantially enriched compared to average seawater. Hydrothermal venting therefore provides bioavailable As by two major pathways throughout Tutum Bay: 1) easily-exchangeable As from hydrothermally influenced sediments to as far away as 200 m from focused venting, and 2) in surface seawaters, which may allow for biological uptake by phytoplankton and transfer up the food web.

Methane-related carbonates formed at submarine hydrothermal springs: a new setting for microbially-derived carbonates?

Numerous small calcite mounds, up to 2.5 m in diameter and 0.75 m in height, accompanied by Ba, Hg and Tl mineralisation, occur in shallow submarine hydrothermal vents on the sea bottom, at 10 m depth, near Punta Mita, on the western coast of Mexico. The hydrothermal activity consists in water and gas (mainly nitrogen and methane) venting at 85°C, through a 100-m-long fissure hosted in basaltic rocks and partially covered by a thin layer of unconsolidated detrital sediments. The mounds consist of travertine-like calcite aggregates that develop around the main submarine hot springs amidst a hydrothermally altered basaltic host rock. Two main calcite generations are texturally recognisable: the first generation shows a radial-fibrous texture; the second is fine-grained calcite, which cements detrital grains and fills the pore spaces. The δ 13C analyses of calcite reveal a strong depletion in 13C, with values as low as −39.2‰ (Vienna PeeDee Belemnite), which suggest that microbial communities may have induced calcite precipitation through microbial methane oxidation. Barite, sulphides (mainly pyrite and cinnabar) and phosphates (carbonate–hydroxylapatite) are also present in the mounds in lower concentrations and form by direct precipitation from the hydrothermal fluid. The Punta Mita hydrothermal carbonate mounds represent a potentially novel environment for microbially induced carbonate mineralisation, which is characterised by high temperatures not encountered in areas of cold seep carbonate formation. Stable isotope results suggest that microorganisms responsible for the oxidation of methane may be present and active at temperatures near 85°C at the Punta Mita vents.

Sulfur isotope geochemistry of the submarine hydrothermalcoastal vents of Punta Mita, Mexico

Coastal hydrothermal submarine vents occur near Punta Mita (Mexico) through a seafloor fissure hosted by basaltic rocks and partially covered by recent sediments. Hydrothermal venting produces calcareous tufa mounds, with minor sulfides, barite and apatite. Pyrite is the most abundant sulfide mineral that precipitates around the submarine hot springs. It occurs as framboids, euhedral crystals, thin botryoidal coatings interbedded with calcite, and as replacement of detrital magnetite grains. Vent fluids have temperature below 100 °C, and methane is abundant. Sulfur isotopic composition of pyrite predominantly has δ 34S values from − 10.7 to +4.9 suggesting that the source of sulfur is microbially reduced sulfate seawater.

Comments on the paper: “Geochemistry of fluids from submarine hot springs at Punta de Mita, Nayarit, Mexico” by Y.A. Taran, S. Inguaggiato, M. Marin, and L.M. Yurova

Comments on the paper: “Geochemistry of fluids from submarine hot springs at Punta de Mita, Nayarit, Mexico” by Y.A. Taran, S. Inguaggiato, M. Marin, and L.M. Yurova