Submarine Hydrothermal Vents Research Articles

Abundance of submarine volcanism in arcs

Explosive submarine arc volcanoes can cause tsunamis, affect climate, and pose hazards to airplanes and ships. Although 70 % of the Earth is submarine, only 15 % of Holocene arc volcanoes in the Smithsonian Global Volcanism database are submarine. Merging locations of active submarine hydrothermal vents in arcs and the above database, we found 71 unlisted submarine arc volcanoes. Using Baker [2017, doi: 10.1016/j.oregeorev.2017.02.006], only 44 % of hydrothermal vents in arcs are known. Only 77 of the vent fields are on volcanoes in the Smithsonian database. Assuming that unknown submarine arc volcanoes are present in the same proportions as unknown vents, there are ~160 as-yet undiscovered Holocene age submarine arc volcanoes. Using geophysical data, we located 291 unsurveyed seamounts <30 km from arc axes, the distance within which active vents occur. We estimate 119±16 have active vents. Because more unknown seamounts exist, this means that >32 % of Holocene arc volcanoes are submarine.

Experimental modelling of the growth of tubular ice brinicles from brine flows under sea ice

Abstract. We present laboratory experiments on the growth of a tubular ice structure surrounding a plume of cold brine that descends under gravity into water with a higher freezing point. Brinicles are geological analogues of these structures found under sea ice in the polar regions on Earth. Brinicles are hypothesized to exist in the oceans of other celestial bodies, and being environments rich in minerals, serve a potentially analogous role as an ecosystem on icy-ocean worlds to that of submarine hydrothermal vents on Earth.

Temperature-controlled Se-S isotope fractionation during seawater mixing and sulfide precipitation in black smoker chimneys

Submarine hydrothermal venting leads to the formation of black smoker chimneys with complex internal zoning. These emerge through mineral precipitation under changing fluid conditions caused by variable degrees of fluid-seawater mixing. This study explores the potential of selenium (Se) isotopes as a novel tool to understand the enrichment processes and identify the sources of chalcophile elements in seafloor hydrothermal systems. In-situ trace element analysis of hydrothermal sulfides combined with high-precision Se and S isotope analysis of micro-domains through the wall of black smoker chimneys from the Nifonea vent field (New Hebrides back-arc, SW Pacific) revealed variations in sulfide chemistry at small spatial resolution. The δ82/76Se values (deviation of 82Se/76Se relative to NIST SRM 3149) of the sulfide micro-domains range from +0.6 to −3.7 ‰ ± 0.2 ‰ (2 s.d.) with a general decrease from the inner chalcopyrite lining towards the outer chimney wall. The highest δ82/76Se values overlap with the mean value of fresh basaltic glass from Nifonea caldera (+0.6 ± 0.4 ‰, n = 4), indicating that Se is primarily leached from the surrounding back-arc basalts. The trace element contents of sulfides revealed systematic variations between vent sites, linked to differences in fluid vapor content induced by sub-seafloor boiling, which did not cause any Se isotope fractionation. Instead, decreasing Se/Tl ratios of pyrite together with decreasing δ82/76Se values of sulfide micro-domains and calculated δ34SH2S fluid values towards the outer chimney wall are indicative of temperature-dependent Se and S isotope fractionation at 370 to <200 °C during fluid-seawater mixing within the chimney wall. This study presents Se isotopes as a new robust instrument to unravel the sources of chalcophile elements and related fluid processes in seawater-diluted hydrothermal systems, enhancing our understanding of their geochemical complexities.

Magnesium silicate chimneys at the Strytan hydrothermal field, Iceland, as analogues for prebiotic chemistry at alkaline submarine hydrothermal vents on the early Earth

The Strytan Hydrothermal Field (SHF) in basaltic terrain in Iceland is one of the extant alkaline submarine hydrothermal vent systems favoured as analogues for where life on Earth may have begun. To test this hypothesis we analyse the composition, structure, and mineralogy of samples from hydrothermal chimneys generated at the SHF. We find that the chimney precipitates are composed of Mg-silicates including clays of the saponite-stevensite group (high Mg and Si, low Fe and Al), Ca-carbonates and Ca-sulfates. The chimneys comprise permeable structures with pores sizes down to 1 µm or less. Their complex interiors as observed with SEM (Scanning Electron Microscopy) and X-ray CT (computed tomography scanning), exhibit high internal surface areas. EDX (energy-dispersive X-ray spectroscopy) analysis reveals an increase in the Mg/Si ratio toward the chimney exteriors. Chemical garden analogue experiments produce similar Mg–silicate chimneys with porous internal structures, indicating that injection-precipitation experiments can be high-fidelity analogues for natural hydrothermal chimneys at the SHF. We conclude that SHF chimneys could have facilitated prebiotic reactions comparable to those proposed for clays and silica gels at putative Hadean to Eoarchean alkaline vents. Analysis of the fluid dynamics shows that these chimneys are intermediate in growth rate compared to faster black smokers though slower than those at Lost City. The SHF is proposed as a prebiotic alkaline vent analogue for basaltic terrains on the early Earth.

Dynamic characteristics of two-vent submarine hydrothermal plumes: A case study of Longqi hydrothermal field

Submarine hydrothermal plumes play an important role in the process of material and energy exchange in the deep sea. Due to the influence of complex environmental factors (multiple vents, deep-sea stratified environment) and the limitation of observation capabilities, the dynamic characteristics of submarine hydrothermal plumes have not been fully understood, and it is urgent to study the diffusion and evolution process of submarine hydrothermal plumes by the computational fluid dynamics (CFD) model. In this paper, a CFD model was established to effectively simulate the diffusion and evolution process of two-vent submarine hydrothermal plumes under the deep-sea stratified environment, obtained the three-dimensional plume flow field structure of two-vent submarine hydrothermal plumes, and obtained the spatial distribution of dynamic characteristics parameters such as velocity, turbulent viscosity, turbulent kinetic energy and turbulence dissipation rate of two-vent submarine hydrothermal plumes. The equations for calculating the maximum plume rise height and the neutrally buoyant plume height of a two-vent submarine hydrothermal plume were deduced and established. In addition, a comparative analysis of the single-vent submarine hydrothermal plume revealed the mechanism of the influence of the key characteristics of the two-vent submarine hydrothermal plumes such as the maximum plume rise height. It was applied to analyze the dynamic characteristics of the plume occurred in Longqi hydrothermal field in the southwest Indian Ocean, and the results were verified by the field observation data. The spatial distribution of mass concentration of hydrothermal plume particles was further analyzed, and the difference of mass concentration in different hydrothermal plume structures was compared to study the exchange mechanism of material and energy between submarine hydrothermal plume and surrounding seawater. The results are of guiding significance for the tracing of submarine hydrothermal vents, the study of marine material exchange and energy transport processes, and the exploration and environmental evaluation of submarine polymetallic sulfide resources.

Sulphate-reducing bacteria-mediated pyrite formation in the Dachang Tongkeng tin polymetallic deposit, Guangxi, China

Mediation by sulphate-reducing bacteria (SRB) is responsible for pyrite (FeS2) formation. The origin of the Dachang tin polymetallic ore field is related to the mineralisation of submarine hydrothermal vent sediments. Here, we investigated SRB in these ores via morphological, chemical, and isotopic analyses. Polarised and scanning electron microscopy indicated that trace SRB fossils in the metal sulphide ore were present in the form of tubular, beaded, and coccoidal bodies comprising FeS2 and were enclosed within a pyrrhotite (FeS) matrix in the vicinity of micro-hydrothermal vents. The carbon (C), nitrogen (N), and oxygen (O) contents in the FeS2 synthesised by SRB were high, and a clear biological Raman signal was detected. No such signals were discerned in the peripheral FeS. This co-occurrence of FeS, FeS2, and the remains of bacteria (probably chemoautotrophic bacteria) was interpreted as the coprecipitation process of SRB-mediated FeS2 formation, which has, to the best of our knowledge, not been reported before. Our study also illustrates that combined energy-dispersive X-ray spectroscopy, Raman spectroscopy, and isotopic analysis can be used as a novel methodology to document microbial-mediated processes of mineral deposition in submarine hydrothermal vent ecology on geological time scales.

Numerical Simulation-Based Analysis of Seafloor Hydrothermal Plumes: A Case Study of the Wocan-1 Hydrothermal Field, Carlsberg Ridge, Northwest Indian Ocean

Understanding the dynamics of deep-sea hydrothermal plumes and the depositional pattern of hydrothermal particles is essential for tracking the submarine hydrothermal venting site, prospecting polymetallic sulfide resources, as well as deciphering biogeochemistry cycling of marine elements. In this paper, a numerical model of the deep-sea hydrothermal plume is established based on the topography and long-term current monitoring data of the Wocan-1 hydrothermal field (WHF-1), Carlsberg Ridge, Northwest Indian Ocean. The model allows for a reconstruction of the hydrothermal plume in terms of its structure, velocity field, and temperature field. The relationships between the maximum height of the rising plume and the background current velocity, and between the height of the neutral-buoyancy layer and the background current velocity are established, respectively. The transport patterns of the hydrothermal particles and their controlling factors are revealed. Using hydrothermal particles with a density of ~5000 kg/m3 (i.e., pyrite grains) as an example, it is found that pyrite larger than 1 mm can only be found near the venting site. Those in the size 0.3–0.5 mm can only be found within 137–240 m from the venting site, while those smaller than 0.2 mm can be transported over long distances of more than 1 km. Using the vertical temperature profiling data of WHF-1 obtained during the Jiaolong submersible diving cruise in March 2017, we reconstruct the past current velocity of 10 cm/s, similar to the current data retrieved from the observational mooring system. Our model and the findings contribute to a better understanding of the hydrothermal system of WHF-1, and provide useful information for tracing the hydrothermal vents, prospecting the submarine polymetallic sulfide resources, designing the long-term observation networks, and relevant studies on element cycling and energy budget.

Linking Catalysis in Biochemical and Geochemical CO2 Fixation at the Emergence of Life

AbstractH2‐producing, submarine hydrothermal vents present a plausible environment for the prebiotic synthesis of the first organic compounds at the emergence of life. Geochemical CO2 reduction at these vent systems harbors similarity to the ancient, biochemical acetyl‐CoA pathway of CO2 fixation in modern autotrophs. Both pathways involve catalytic transformations with transition metals as active centers. This concept article provides some insight about origins of life, mineral‐catalyzed CO2 reduction, and its correlation to the enzymatic pathway by focusing on key studies.

The influence of submarine hydrothermal systems on seawater sulfate

Seawater sulfate is a major carrier of oxidizing capacity and influences the redox budget of the Earth’s surface on geologic timescales. Records of oxygen and sulfur isotopes in seawater sulfate are used to track changes in sulfate cycling through geologic time. Interpretations of these records are typically based on models that describe the seawater sulfate reservoir as a mass balance between microbial, riverine and sedimentary sulfate fluxes. Here, we investigate the influence of hydrothermal sulfate cycling, which remains an unconstrained but potentially significant additional flux in this mass balance. We find that anhydrite (CaSO4) from eight submarine hydrothermal vent fields is consistently offset from seawater sulfate in δ18O but not Δ’17O or δ34S. Experiments at hydrothermal pressure–temperature conditions indicate that this δ18O offset is driven by oxygen isotope exchange between sulfate and hydrothermal H2O at high temperature. An updated isotope mass balance model shows that a flux of hydrothermal sulfate into seawater, derived from retrograde dissolution of hydrothermal anhydrite, could cause high-temperature oxygen isotope exchange to buffer seawater sulfate δ18O and Δ’17O by as much as 25%. Hydrothermal sulfate preserved in the Troodos Ophiolite (Cretaceous) also records a δ18O and Δ’17O signal of high-temperature oxygen isotope exchange, supporting the conclusion that geologic records of seawater sulfate oxygen isotopes may include a hydrothermal component.

2H-2H clumping in molecular hydrogen method and preliminary results

We present a method for measuring the clumped isotope composition of molecular hydrogen (H2) using a high-resolution mass spectrometer, the Thermo 253 Ultra, improved to address subtle artifacts arising from instrument baselines and non-linear responses. We also present methods for purification and concentration of H2 from natural and experimental samples, tailored to this measurement. We document the accuracy of the method through comparison to established methods for the determination of δD values, and through measurements of H2 gases of widely varying D content that were driven to isotopic equilibrium with respect to their distributions of isotopologues by heating in the presence of a catalyst. Experimental reproducibility of δD and ΔDD values over months averages ±0.5 and ± 6.9 ‰, respectively (1σ) — both small fractions of common natural variations. We explore methods of gas purification and handling, and show that preferred methods result in low (0–4 ‰) changes in δD and undetectable changes in ΔDD. Our methods and data processing procedures were further tested by comparing measurements of mixtures of H2 gases that varied widely in δD and ∆DD with a model describing proportions of isotopologues in such mixtures. Application of these methods to H2 that is residual to laboratory consumption by cultured methanogens shows that metabolic ‘back reaction’ (metabolic production of H2 from water-derived protons during net H2 consumption) is responsible for driving the ΔDD value of residual H2 toward equilibrium at environmental temperatures. Finally, we report the first measurements of the clumped isotope composition of molecular hydrogen in natural geological samples collected from high and low temperature submarine hydrothermal vents (Lost city, Rainbow, Ashadze) and an intracontinental natural reservoir in Mali; initial findings suggest that ∆DD of H2 generally records temperatures of fluid venting or long-term storage, even in cases where the δD of H2 has not equilibrated with water at those temperatures. This study establishes the first clumped isotope systematics of molecular hydrogen based on both experimental and natural samples, including key processes in the biogeochemical cycle of H2.

Cyclic tidalites and seismites at a submarine hydrothermal system for a 2450 Ma banded iron formation, Hamersley Basin, Western Australia

The Hamersley Group in the Hamersley Basin, Western Australia, contains major deposits of banded iron formation of Neoarchean–Paleoproterozoic age (2629–2449 Ma). The 2450 Ma Weeli Wolli Formation near the top of the group includes banded iron formation with microbands (≤0.05–0.5 mm to rarely 1 mm thick) of chert and iron oxide lamina couplets that display distinctive cycles. Some adjacent, thin microbands have merged with compaction and the diagenetic removal of chert laminae, and maximum counts of cycle period by different studies is preferred, suggesting a period of ∼28 ± 2 microbands. Associated cyclic iron formation shows soft-sediment plastic deformation and brittle fracturing. Rare earth element geochemistry indicates that much of the iron in late Archean–early Paleoproterozoic banded iron formations was derived from submarine hydrothermal systems. Monitoring of hydrothermal vents on mid-ocean ridges and seamounts has identified tidal modulation of the discharge, temperature and dispersal of deep-sea hydrothermal plumes principally by semidiurnal variations in tidal loading and earth tides. Microearthquake swarms are associated with deep-sea hydrothermal systems at the crests of mid-ocean ridges, and tidal triggering of microearthquake activity is indicated for a hydrothermal system on the East Pacific Rise. The microband cycles in the Weeli Wolli Formation are interpreted as tidalites, comprising ∼28 ± 2 semidiurnal microbands per lunar (synodic) fortnightly cycle, related to the tidally modulated activity of a submarine hydrothermal system. The associated plastically deformed and brittle-fractured sediments are viewed as seismites resulting from microearthquakes also related to the hydrothermal system. The Weeli Wolli microband cycles and seismites may represent a rarely identified instance of iron-formation deposition near a submarine hydrothermal system. KEY POINTS Submarine hydrothermal venting was a major source of iron in late Archean–early Paleoproterozoic banded iron formations. Semidiurnal variations in tidal loading and earth tides commonly modulate present-day deep-sea hydrothermal activity, and microearthquake swarms are associated with deep-sea hydrothermal systems. Early Paleoproterozoic banded iron formation from the Hamersley Basin displays cycles with an estimated period of ∼28 ± 2 microbands and associated plastic deformation and brittle fracturing. The microband cycles are interpreted as tidalites comprising ∼28 ± 2 semidiurnal increments grouped in fortnightly cycles at a tidally modulated submarine hydrothermal system, and the deformed sediments as seismites caused by related microearthquake activity.

Enrichment of mercury in the Lower Cambrian sedimentary successions by submarine hydrothermal venting

• Widespread sedimentary Hg enrichments in the Early Cambrian can be attributed to periodic hydrothermal ventilation. • Prevailing hydrothermal ventilation was an important source of Hg in sediments in the Early Cambrian. • The accumulation of Hg in sediments may be more effective in euxinic environments. Although extremely high Hg contents are known in the Lower Cambrian sedimentary successions, the extent and spatial-temporal distribution of sedimentary Hg anomalies in these successions remain unclear. Here, we report concentrations of Hg, total organic carbon (TOC), total sulfur (TS), and major and rare earth elements of the Lower Cambrian (∼525 Ma) sedimentary rocks at the Dongxihe section in the interior of the Yangtze Platform, South China. We investigated the sedimentary Hg enrichment mechanism and the spatial-temporal fluctuations of Hg in the Lower Cambrian and compiled published Hg (Hg/TOC) data from the Upper Neoproterozoic to the Lower Cambrian to trace the potential Hg sources. Our study verified that hydrothermal vents provide an excess Hg source for the sedimentary Hg enrichment in the Dongxihe section, which is supported by the positive Eu anomaly and major element. The major elements show more Fe and Mn enrichment in the upper part than the lower part, indicating more hydrothermal contribution in the upper part. Additionally, the records of the spatial-temporal distribution of Hg show that most of the sections (including shelf, slope, and basin) in South China show strong sedimentary Hg enrichment, which can be attributed to widespread hydrothermal venting. By reconstructing fluctuations of Hg during the Late Neoproterozoic to the Early Cambrian, we proposed that in the context of the Gondwana continent assembly, the prevalent hydrothermal ventilation event during the Early Cambrian not only induced the abnormal enrichment of sedimentary Hg but also played a crucial role in shaping the marine environment and ecosystem during this period.

Molecular evidence reveals the presence of hydrothermal effect on ultra-deep-preserved organic compounds

Hydrothermal alteration, transformation and synthesis of organic compounds have long been noted in submarine hydrothermal vents, terrestrial hot springs, epithermal deposits and laboratories. However, little is documented about the influence of deep hydrothermal activities on organic compounds at the ultra-deep horizon. It remains unclear to what extent the compounds are hydrothermally (secondarily) affected. Here we report molecular and isotopic level analyses of liquid oils derived from an ultra-deep reservoir in the Tarim Craton, south of the Central Asian Orogenic Belt. The organic compounds had an unexpectedly convoluted molecular and isotopic geochemistry, suggesting that the deep hydrothermal activities impact the organic compounds to varying degrees. In the absence of severe gas washing, in-reservoir mixing and thermochemical sulfate reduction, hydrothermal alteration results in a progressive increase in the relative abundance of organosulfur compounds. The transformation of three compound classes (e.g., phenanthrene ring systems, biphenyl ring systems and dibenzothiophene ring systems) during hydrothermal alteration was observed. As the extent of the hydrothermal effect increases, dibenzothiophene ring systems are favourably formed through the oxidation of phenanthrene ring systems, followed by the incorporation of sulfur from biphenyl ring systems that were less thermally stable. The spatial variation in the hydrothermal effect was decoupled from other thermogenic effects. A new perspective regarding the hydrothermal effect on molecular and isotopic compositions may shed light on the organic–inorganic interactions of deep-sourced organic fluids with their aqueous and mineralogical environments, and the temporal and spatial variation in organic signals and environments at known hydrothermal systems on Earth, Mars and even Titan.

Geochemistry of trace metals and Rare Earth Elements in shallow marine water affected by hydrothermal fluids at Vulcano (Aeolian Islands, Italy)

Trace metals and Rare Earth Element (REE) are amply discharged by submarine hydrothermal vents, sometimes leading to the formation of ore deposits of economic interest. We report on first data on the geochemical processes involving REE and trace metals, at the solid-liquid interface, in the hydrothermal area of Levante Bay at Vulcano Island (Aeolian Archipelago, Italy). Samples were collected from several submarine springs and seeps, a mud pool and one thermal well, and analyzed for Al, Si, Ti, V, Cr, Mn, Fe, Co, As, Rb, Sr, Cs, Ba, U and REE, besides major ions.Within the bay, hydrothermal fluids contaminate seawater and promote the leaching of metals from sediments through the dissolution of CO2 and H2S, while the particulate matter removes several elements from the water. The leaching of the bottom sediments and the contribution of steam-heated water produce an enrichment of some metals and REE in the Levante Bay with respect to the concentrations expected in the ambient seawater. An enrichment up to one order of magnitude is measured for Fe, Al, Ba, Cs and Rb, and up to two orders of magnitude for Mn in the submarine samples. Other transition metals (Ti, V, Co, Cr), U, As and Sr have concentrations similar or slightly lower than the ambient seawater. REE are in concentrations higher than in ambient seawater up to two orders of magnitude. Despite being significantly higher than uncontaminated seawater, the concentrations of some metals (namely Fe, Al, Ti, Cr, V, Co, U) and REE in most samples are lower than expected by the mixing between seawater and the steam-heated water, discharging from submarine springs. Indeed, equilibrium and reaction path modeling indicate the likely precipitation of Fe-oxyhydroxides, able to remove minor elements, such as Ti, Cr, Co, V and As, and REE. The last ones are significantly removed by newly-forming solid phases, due to the presence of a large amount of Fe released by the acidic fluids through the leaching of sediments. The low pH limits the formation of solution complexes of REE with carbonate ions (the main complexing agent for REE in seawater), whereas the sorption onto particles is still effective, even at close distance from the submarine springs and seeps.This study brings new insights on the geochemical processes occurring in submarine hydrothermal systems, in particular, those in subduction-related context.

Submarine hydrothermal vent systems: the relevance of dynamic systems in chemical evolution and prebiotic chemistry experiments

AbstractSince their discovery, submarine hydrothermal vent systems have been pointed out as important places where chemical evolution on Earth could have occurred; and their role in the process has been highlighted. Similarly, some hypotheses have considered these systems in origin of life scenarios. In this way, many experiments have been developed, and the knowledge about these systems has increased. Due to their complexity, many experimental simulations have only included a few of the geochemical variables present in these environments, pressure and temperature. Other main variables have hardly been included, such as mineralogy, thermal and pH gradients, dissolved ions and/or redox reactions. As it has been understood, the dynamism and heterogeneity of these environments are huge, and it comprises different scales, from single vents to full hydrothermal fields. However, the vast majority of experiments focus on a specific part of these systems and do not include salinity, mineralogy and pH gradients. For this reason, in this paper, we pointed out some considerations about how this dynamism can be interpreted, and included in some models, as well their importance in prebiotic chemistry experiments and their extrapolations regarding the hypothesis about the origins of life.

Flow fields and outputs of the hydrothermal plume at the Wocan-1 field based on an &amp;lt;italic&amp;gt;in-situ&amp;lt;/italic&amp;gt; video

<p indent="0mm">Deep-sea hydrothermal plumes are an essential medium for exchanging the heat and elements between the lithosphere and hydrosphere and contribute to elemental cycling and marine chemistry evolution. In this paper, based on field video footage of a black smoker recorded at the Wocan-1 hydrothermal field on the slow-spreading Carlsberg Ridge in the northwestern Indian Ocean, the flow fields of the “Huoyanshan” hydrothermal plume were calculated using a cross-correlation algorithm. In addition, the heat and chemical outputs of the hydrothermal vent are investigated using the estimated source volume flux and fluid properties obtained from <italic>in-situ</italic> measurements. The results reveal that as the plume rises, the vertical velocity along the plume centerline increases, reaching a maximum value of approximately <sc>15.5 cm/s.</sc> This tendency is attributed to the combined effect of initial momentum flux and buoyancy flux. The maximum horizontal velocity along the plume centerline is approximately <sc>10.3 cm/s,</sc> indicating a strong deep ocean current on the Carlsberg Ridge. Due to plume entrainment, the volume flux of the hydrothermal vent linearly increases with increasing plume rise. Furthermore, the heat and iron outputs from the “Huoyanshan” hydrothermal vent were estimated as <sc>1.35±0.11 MW</sc> and <sc>3661±323 kg/a,</sc> respectively. These results provide valuable insights into the plume dynamics of submarine hydrothermal vents and the deep-sea thermal and elements balance.

Interaction of CO2 with well-ordered iron sulfide films on Au(111)

Iron sulfides are important in catalysis because of their abundance on earth and their catalytic activity. In Wächtershäuser’s origin of life theory, Fe/Ni sulfide deposits in and near to submarine hydrothermal vents (’black smokers’) catalyzed the production of first organic matter, and recent studies have indicated that iron sulfides might be able to activate CO2 towards conversion into chemicals such as methanol, formic acids and others. Here, we present a study of the interaction of carbon dioxide with well ordered iron sulfide films grown on Au(111). Since the as-prepared film proved to be rather non-reactive to the molecule, possibly because of the layer’s sulfide termination, we tried to modify the sulfide’s stoichiometry both by exposing it to atomic hydrogen and by adding metallic iron. Hydrogen is able to interact with the sulfur on the surface and to partially remove it, but the resulting surface is still not reactive towards CO2. X-ray photoemission results show that the addition of metallic iron is detrimental for the quality of the sample, giving rise to the admixture of substrate gold to the layer. Insertion of an FeO blocking layer between the sulfide and the gold substrate allowed the sulfide to become Fe-rich, enhancing its reactivity towards CO2, but it was not possible to completely prevent diffusion between the FeO layer and the substrate. However, we found that an increased iron content together with the presence of gold was able to activate the layer towards CO2.

Mechanisms and rates of pyrite formation from hydrothermal fluid revealed by iron isotopes

Critical to interpreting iron isotope signatures in hydrothermal sulfide minerals is the accurate knowledge of Fe isotope fractionation factors, both kinetic and at equilibrium, between the fluid and minerals. Here we report Fe isotope fractionation between pyrite and aqueous saline fluid from in-situ pyrite precipitation experiments performed at 400–450 °C and 400–800 bar in a wide range of pH (2.5–4.8) and salt content (0.05–2.0 mol NaCl/KCl per kg of fluid). Our measurements show that while apparent bulk chemical equilibrium (in terms of total dissolved Fe concentration) between the FeCl2-bearing fluid and crystalline pyrite is attained within a few days, the Fe isotope fractionation values between the fluid and mineral (expressed as Δ57Fefluid-pyrite = δ57Fefluid – δ57Fepyrite) exhibit large variations, from about –0.6 to +1.0‰, depending on the elapsed time (1–30 days) and fluid composition (mostly pH, sulfur solubility, and di- and tri-sulfur radical ion concentration). Yet these values remain significantly higher, by 0.5–2‰, than equilibrium isotope fractionation inferred from β-factors of pyrite and the dominant iron chloride species in solution FeCl2(H2O)20(aq), generated in this study using Density Functional Theory (DFT) modeling (Δ57FeFeCl2(H2O)2-pyrite ≈ –1.25 ± 0.25‰ at 300–450 °C). The lack of isotope equilibrium between fluid and pyrite in this study and other recent work demonstrates that the fluid-pyrite Fe isotope exchange is kinetically controlled even at elevated temperatures (≥300 °C), allowing rate patterns to be identified. Our time-series data, combined with other available measurements at 300–350 °C, provide evidence for two major distinct kinetic regimes of fluid-pyrite Fe isotope exchange: (1) a fast and short (<10–20 days) initial step, likely controlled by Fe (poly)sulfide aqueous precursors that transfer their isotope signature to rapidly precipitating pyrite resulting in apparent isotopic disequilibrium between the FeCl2-dominated fluid and pyrite, (2) followed by a slower and longer second step of pyrite recrystallization, growth, and isotope re-equilibration with the fluid. The derived Fe isotope exchange rate constants suggest that more than 1 year is required to isotopically equilibrate pyrite with hydrothermal fluid at temperatures of 300–450 °C. Our new data provide direct interpretation of the Fe isotope ratios in fluids and sulfide minerals from modern submarine hydrothermal vents, which are characterized by fast (hours to days) pyrite precipitation. Furthermore, our results may enable estimating, using Fe isotope signatures, the dynamics of relatively short (<year-scale) mineralizing events in ancient hydrothermal metal sulfide deposits that cannot be assessed using more traditional dating approaches.

Understanding hydrothermal behavior of the Maneadero geothermal system, Ensenada, Baja California, Mexico

A hydrogeological conceptual model has been developed that describes the geothermal system located at the Maneadero region in Ensenada, Baja California, Mexico. In addition, a two-dimensional steady state simulation of water flow and heat transfer of a model profile using COMSOL Multiphysics software is also presented. The proposed hydrogeological conceptual model considers that the old local anoxic subsurface seawater feeds the system, and a remnant magmatic intrusion in the surface from past volcanism at 2 km of depth works as heat source. The intersection between the south Agua Blanca Fault and the L3 alignment promote the fluids ascent to the submarine hydrothermal vent. The results of the simulation show a reservoir temperature of 164 °C and an affluent temperature of 105 °C, varying between 1 °C and 3 °C, respectively, with previous studies. Moreover, a geothermal potential of 0.48 MW was estimated for the simulated profile. The current policy of exploitation of geothermal resources in Mexico makes the development of these models particularly relevant, serving as a tool for their evaluation and management.

The Role of Meteorite Impacts in the Origin of Life.

The conditions, timing, and setting for the origin of life on Earth and whether life exists elsewhere in our solar system and beyond represent some of the most fundamental scientific questions of our time. Although the bombardment of planets and satellites by asteroids and comets has long been viewed as a destructive process that would have presented a barrier to the emergence of life and frustrated or extinguished life, we provide a comprehensive synthesis of data and observations on the beneficial role of impacts in a wide range of prebiotic and biological processes. In the context of previously proposed environments for the origin of life on Earth, we discuss how meteorite impacts can generate both subaerial and submarine hydrothermal vents, abundant hydrothermal–sedimentary settings, and impact analogues for volcanic pumice rafts and splash pools. Impact events can also deliver and/or generate many of the necessary chemical ingredients for life and catalytic substrates such as clays as well. The role that impact cratering plays in fracturing planetary crusts and its effects on deep subsurface habitats for life are also discussed. In summary, we propose that meteorite impact events are a fundamental geobiological process in planetary evolution that played an important role in the origin of life on Earth. We conclude with the recommendation that impact craters should be considered prime sites in the search for evidence of past life on Mars. Furthermore, unlike other geological processes such as volcanism or plate tectonics, impact cratering is ubiquitous on planetary bodies throughout the Universe and is independent of size, composition, and distance from the host star. Impact events thus provide a mechanism with the potential to generate habitable planets, moons, and asteroids throughout the Solar System and beyond.