Superheated Fluids Research Articles

Seafloor spreading and the delivery of sulfur and metals to Earth’s oceans

Abstract Circulating fluids within Earth’s mid-ocean ridge system cool and alter the oceanic crust, contribute distinct chemistry to the ocean, and generate economically and geologically important metal-sulfide deposits at the seafloor. Yet, we have few constraints on the characteristics of these fluids at peak subseafloor pressure and temperature conditions or how the primary variable, seafloor spreading, affects these fluids’ delivery of metals and sulfur to seawater. Here, we develop a new, robust technique for estimating the peak endowment of heat and dissolved sulfur, iron, and copper in subseafloor hydrothermal fluids and determining their fate as these superheated fluids rise to the seafloor. Calculations using this technique indicate that >20%–70% of sulfur, iron, and copper dissolved at peak subseafloor conditions are lost during upflow due to cooling and concomitant decreases in sulfide mineral solubility. The interpretation of these estimates within the geologic context of vent fields allows us to demonstrate a strong inverse relationship between seafloor spreading rate and peak pressure-temperature conditions, subseafloor heat loss, and the magnitude of subseafloor sulfide mineralization. Our results demonstrate the extent to which the secular variation of Earth’s mid-ocean ridge system over geologic time has impacted sulfide deposition rates and hydrothermal fluxes of sulfur and metals to the ocean.

Natural explosion structures in rocks

We have observed, in a few hydrothermal breccia bodies near Hong Kong, many peculiar natural explosion structures that bear a strong resemblance to the fracturing patterns produced by quarry blasting. The structures, occurring in hydrothermally altered late Mesozoic volcanic and sedimentary rocks, range in size from a few cm to about 80 cm in diameter, and exhibit a central cavity, a crushed zone around the central cavity, and a radial-crack zone like those formed by explosive blasting. A damage boundary marking the outer extent of the radial fractures is sometimes present. Some of the structures are affected by pre-existing cracks, with the damage boundary stretched in the direction of the crack. Results from detailed field measurements of the morphology, geometric characteristics, and orientations of over a hundred such explosion structures show a spherical geometry of the structure. These natural explosion structures probably formed when rapidly ascending superheated fluids reached the boiling curve, which led to depressurization of the fluids and expanding vapor explosions. The formation mechanism and thermodynamic implications are discussed in this paper, which is the first report of such naturally formed vapor explosion structures in rocks.

Time‐Lapse Geophysical Investigation of Geyser Dynamics at Spouter Geyser, Yellowstone National Park: Geyser Dynamics II

AbstractGeysers are unique hydrothermal features, requiring specific geometry, fluid, and vapor input, and heat to produce eruptions. In a geyser eruption, the decompression of superheated hydrothermal fluids results in a conversion of thermal to kinetic energy. Recent studies conclude that a laterally offset cavity structure (bubble trap) plays an integral role in the geyser eruption process. In this second study of Spouter Geyser, Yellowstone National Park (YNP), we build on the geyser structure developed in the first publication and explore how structural components, such as the bubble trap, control eruption dynamics. We utilize time‐lapse electrical resistivity tomography (ERT) and transient electromagnetics (TEM) geophysical methods to track changes in the saturation of conductive hydrothermal fluid and resistive vapor through the eruption cycle. Additionally, we use pressure‐temperature transducer data to measure eruption and recharge durations over the past 23 years at Spouter Geyser, identifying long‐period trends in geyser behavior. The geophysics results support the bubble trap model, capturing an increase in resistivity in the bubble trap structure during the recharge phase interpreted as a vapor saturation increase. The TEM also captures a resistivity increase in the 20–30 m depth interval during the eruption phase, interpreted as a vapor‐dominated “flash eruption zone” where the superheated hydrothermal fluids flash into steam and drive fluid out of this zone during the eruption. From the temperature time‐series detailing 23 years of eruption and recharge durations, we find that eruption durations have remained constant at ∼2 hr while recharge durations have decreased linearly at 6.6 min/year.

Cryogenic test bench for the experimental investigation of cryogenic injection in rocket combusters under high-altitude conditions

Due to current and future environmental and safety issues in space propulsion, typical propellants for upper stage or satellite rocket engines such as the toxic hydrazine are going to be replaced by green propellants like the combination of liquid oxygen and hydrogen or methane. The injection of that kind of cryogenic fluid into the vacuum atmosphere of space leads to a superheated state, which results in a sudden and eruptive atomization due to flash boiling. For a detailed experimental investigation of superheated cryogenic fluids the new cryogenic test bench M3.3 with a temperature controlled injection system at high-altitude conditions was built at DLR Lampoldshausen. First run-in tests as well as several measurement campaigns with liquid nitrogen as the test fluid showed the performance and suitability of the new test bench for the systematical investigation of cryogenic flash boiling. Besides new insights into the flash boiling process of cryogenic liquids, the experimental data of cryogenic flash boiling generated with this test bench provide a comprehensive database for the validation of numerical models and further numerical investigations.

Silica scaling and boiling effect on corrosion behaviour of nickel-based alloys associated with superheated hydrothermal fluids containing HCl, H2S and CO2

The effect of amorphous silica (AM-silica) surface deposits on the corrosion behaviour of two nickel-based alloys associated with superheated hydrothermal fluid containing sour gases (HCl, H2S and CO2) was investigated experimentally at 350 °C at 10 barG. The results demonstrate that the AM-silica scales do not promote localized corrosion damage whereas some corrosion products were detected in non-scale samples due to fluid boiling from sub- to superheated conditions. This study contributes to more understanding of the effect of amorphous silica scaling and boiling on corrosion behaviour and the selection of materials for future application in superheated geothermal systems.

Heat transfer enhancement in superheated hydrocarbon fluids due to traces of water

For the specific mode of pulse heating of a wire probe immersed in a test liquid (saturated hydrocarbon), the effect of enhancement of the heat transfer through the probe surface has been revealed. The characteristic heating time is from 10 to 20 ms. The objects of research are n-hexane, n-decane, and n-hexadecane. It is shown that the addition of 0.003% water increases the heat transfer to 10% in the course of approaching the boiling-up temperature of liquid. Simulation of the experimental conditions shows the possibility of microconvection in the most heated boundary layer of a liquid about 10 μm thick.

Droplet velocity and diameter distributions in flash boiling liquid nitrogen jets by means of phase Doppler diagnostics

Due to current and future environmental and safety issues in space propulsion, typical propellants for upper stage or satellite rocket engines such as the toxic hydrazine are going to be replaced by green propellants like the combination of liquid oxygen and hydrogen or methane. The injection of that kind of cryogenic fluids into the vacuum atmosphere of space leads to a superheated state, which results in a sudden and eruptive atomization due to flash boiling. For a detailed experimental investigation of superheated cryogenic fluids, the new cryogenic test bench M3.3 with a temperature controlled injection system was built at DLR Lampoldshausen. After a first test campaign with high-speed shadowgraphy of flash boiling liquid nitrogen sprays, a laser-based Phase Doppler system was set-up to determine the spatial distributions of droplet velocities and diameters in highly superheated sprays. The spatial distributions revealed a core region with high mean velocities close to the injector orifice. With increasing distance from the injector orifice, the sprays develop a more and more monodisperse pattern. These distributions also showed that atomization due to flash boiling generates finer sprays with growing degrees of superheat. In certain spray regions, two droplet populations varying in their direction of motion, velocity and diameter due to possible recirculation zones were observed. The experimental data of flash boiling liquid nitrogen generated within this study provide a comprehensive data base for the validation of numerical models and further numerical investigations.Graphic abstract

The link between hydrothermal nickel mineralization and an iron oxide-copper–gold (IOCG) system: Constraints based on mineral chemistry in the Jatobá deposit, Carajás Province

The Jatobá deposit represents a specific portion of an Archean-Paleoproterozoic iron oxide–copper–gold system, notable due to its hydrothermal nickel-rich zones. Neoarchean mafic and acid volcanic rocks of the Itacaiúnas Supergroup host the mineralized zones. Pre-, syn- and late shearing hydrothermal alteration, associated with the Canaã shear zone development, was pervasive and intense. Early distal hydrothermal alteration encompasses potassic-iron-silica (quartz–biotite–magnetite–apatite), sodic (albite, scapolite), and sodic-calcic (ferro-pargasite) alteration. The main syn-tectonic hydrothermal alteration stage resulted in scapolite–hastingsite–biotite controlled by the mylonitic foliation. Syn-deformation massive magnetite bodies represent proximal envelopes of the mineralized zones. They were intercepted by actinolite-apatite-magnetite and potassic-iron (biotite–magnetite) alteration fronts. Late tectonic hydrothermal alteration comprises chlorite–(epidote–quartz–calcite), fibrous scapolite veins, and green biotite–scapolite–F-Cl-apatite veinlets. The copper–(nickel) mineralized zones in the Jatobá deposit were formed in four stages, coeval to ductile and ductile-brittle deformational events. The mineralization stage (I), spatially related to massive magnetite–(apatite–actinolite) bodies, has the highest nickel content. It is characterized by Ni-pyrrhotite, Ni-pyrite, and subordinately, Co-chalcopyrite, Ce-allanite, Co-pentlandite, and Ce-monazite. The mineralization style evolved from replacement fronts controlled by the mylonitic foliation to hydraulic breccia zones. The mineralization stage (II) was synchronous to the development of syn-tectonic potassic-iron alteration and Co-chalcopyrite (±Ni-pyrite ± Ni-pyrrhotite). The mineralization stage (III), controlled by ductile-brittle and brittle structures, enabled the formation of veins with typical open-space filling textures infilled by paler brown or green biotite, Co-chalcopyrite, and siegenite (±Co-pyrite, ±Co-magnetite, ± cassiterite). The late mineralization stage (IV), coeval to widespread chlorite alteration, formed the most important copper mineralization at Jatobá. It is represented by branching veinlets and breccias with chalcopyrite, Co-chalcopyrite, Co-pyrite, sphalerite, molybdenite, uraninite, monazite, W-bearing hematite, and rare earth carbonates (bastnäsite, coskrenite, and sahamalite). The high chlorine contents of halogen-rich minerals (e.g., scapolite, biotite, apatite, and amphibole) imply the participation of highly saline, supersaturated fluids in the system evolution. Metalliferous fluids were highly focused, and mineralized zones represent the hotter hydrothermal centers. The high V and Ti contents in magnetite and its coexistence with hercynite and ilmenite indicate temperatures above 600 °C. These conditions would be similar to that of magnetite formed in the transition from magmatic to deep magmatic-hydrothermal systems, including the IOA deposits, especially on the onset of the early nickel-enriched mineralization stage. Such conditions enabled nickel leaching from mafic and mafic-ultramafic rocks, its transport in Cl-rich hydrothermal fluids, and precipitation related to episodic decompression. Temperature decrease (<380 °C), indicated by chlorite geothermometers, favored the bulk of chalcopyrite precipitation in late mineralization stages. The Jatobá deposit has attributes comparable to those of relatively deep portions of IOCG mineral systems formed from the channeling of overpressured superheated deep-seated fluids of probable magmatic origin.

Seeding approach to bubble nucleation in superheated Lennard-Jones fluids

We investigate vapor homogeneous nucleation in a superheated Lennard-Jones liquid with computer simulations. Special simulation techniques are required to address this study since the nucleation of a critical vapor bubble-one that has an equal chance to grow or shrink-in a moderately superheated liquid is a rare event. We use the Seeding method, which combines Classical Nucleation Theory with computer simulations of a liquid containing a vapor bubble to provide bubble nucleation rates in a wide temperature range. Seeding has been successfully applied to investigate the nucleation of crystals in supercooled fluids, and here we apply it to the liquid-to-vapor transition. We find that the Seeding method provides nucleation rates that are consistent with independent calculations not based on the assumptions of Classical Nucleation Theory. Different criteria to determine the radius of the critical bubble give different rate values. The accuracy of each criterion depends of the degree of superheating. Moreover, seeding simulations show that the surface tension depends on pressure for a given temperature. Therefore, using Classical Nucleation Theory with the coexistence surface tension does not provide good estimates of the nucleation rate.

Development and characterization of a compact rig to test expanders for superheated and saturated organic fluids

The power production from the conversion of heat at low and medium temperature is a viable way to recover energy from several industrial and utility processes. In this context, small-medium expanders for Organic Rankine Cycles and two-phase expanders for energy recovery in heat pumps are gathering an increasing attention. The design and setup of flexible test benches to carry out experimental investigations on these devices has a primary importance to their performance optimization. In this study, a test rig based on a hot gas bypass cycle to test expanders for superheated and two-phase organic fluids is proposed. This configuration leads to numerous advantages like compact design, high flexibility and a fast transition to stable steady conditions. After an experimental campaign to assess the correct response of the test bench in design condition, a numerical model was developed to study the behavior of the cycle. The management of the test rig, both with and without the expanders, for performing the tests at different operating conditions was analyzed, with particular focus on the required setting of valves and compressor.The analysis allowed the determination of the operating limits of the rig, and showed the impact of using different fluids in the same test rig at several operating conditions. The working range of the test bench is related to the condenser power (designed for 25 kW and 30 bar maximum pressure) and the ambient temperature. With R404A, in the 17–30 bars condenser pressure range, superheated and saturated vapor expanders may be tested at different values of cycle minimum pressure (between 3.7–7.2 bar and 3.6–6.4 bar respectively). With R410A the working range is narrower, with the possibility of testing 2 phase expanders between 6.4 and 8.7 bars of cycle minimum pressure in the 21–23 bars interval of condenser pressure and superheated vapor expanders between 5.7 and 7.2 bars of cycle minimum pressure in the 23–30 bars interval of condenser pressure.

Xenon bubble chambers for direct dark matter detection

The search for dark matter is one of today's most exciting fields. As bigger detectors are being built to increase their sensitivity, background reduction is an ever more challenging issue. To this end, a new type of dark matter detector is proposed, a xenon bubble chamber, which would combine the strengths of liquid xenon TPCs, namely event by event energy resolution, with those of a bubble chamber, namely insensitivity to electronic recoils. In addition, it would be the first time ever that a dark matter detector is active on all three detection channels, ionization and scintillation characteristic of xenon detectors, and heat through bubble formation in superheated fluids. Preliminary simulations show that, depending on threshold, a discrimination of 99.99% to 99.9999+% can be achieved, which is on par or better than many current experiments. A prototype is being built at the University at Albany, SUNY. The prototype is currently undergoing seals, thermal, and compression testing.

Microbial biofilms associated with fluid chemistry and megafaunal colonization at post-eruptive deep-sea hydrothermal vents

At deep-sea hydrothermal vents, reduced, super-heated hydrothermal fluids mix with cold, oxygenated seawater. This creates temperature and chemical gradients that support chemosynthetic primary production and a biomass-rich community of invertebrates. In late 2005/early 2006 an eruption occurred on the East Pacific Rise at 9°50′N, 104°17′W. Direct observations of the post-eruptive diffuse-flow vents indicated that the earliest colonizers were microbial biofilms. Two cruises in 2006 and 2007 allowed us to monitor and sample the early steps of ecosystem recovery. The main objective of this work was to characterize the composition of microbial biofilms in relation to the temperature and chemistry of the hydrothermal fluids and the observed patterns of megafaunal colonization. The area selected for this study had local seafloor habitats of active diffuse flow (in-flow) interrupted by adjacent habitats with no apparent expulsion of hydrothermal fluids (no-flow). The in-flow habitats were characterized by higher temperatures (1.6–25.2°C) and H2S concentrations (up to 67.3µM) than the no-flow habitats, and the microbial biofilms were dominated by chemosynthetic Epsilonproteobacteria. The no-flow habitats had much lower temperatures (1.2–5.2°C) and H2S concentrations (0.3–2.9µM), and Gammaproteobacteria dominated the biofilms. Siboglinid tubeworms colonized only in-flow habitats, while they were absent at the no-flow areas, suggesting a correlation between siboglinid tubeworm colonization, active hydrothermal flow, and the composition of chemosynthetic microbial biofilms.

Resistivity characterization of the Krafla and Hengill geothermal fields through 3D MT inverse modeling

Krafla and Hengill volcanic complexes, located 300km apart, are both known as high-temperature geothermal systems located within neo-volcanic zones of Iceland. This paper demonstrates the utilization of three-dimensional (3D) magnetotelluric (MT) inversions from three different inverse modeling algorithms, which leads to characterizing the electrical resistivity structure of geothermal reservoirs with a much greater level of confidence in accuracy and resolution than if a single algorithm was employed in the data interpretation. These are the first 3D MT inversions of a Krafla MT dataset. The inverted model of electrical resistivity is a classic example of a high-temperature hydrothermal system, with a highly resistive near-surface layer, identified as unaltered porous basalt, overlying a low resistivity cap corresponding to the smectite–zeolite zone. This layer is in turn underlain by a more resistive zone, identified as the epidote–chlorite zone, also called the resistive core, which is often associated with production of geothermal fluids. The electrical structure in the upper 1–2km does not correlate with lithology but with alteration mineralogy. At the location of the IDDP-1 well, which encountered magma at 2.1km depth, the resistivity image shows high resistivity, most likely due to the epidote–chlorite geology and the presence of deeper superheated or supercritical fluids. Two km northwest of the well, however, an intrusive low-resistivity feature is imaged rising from depth, and a plausible interpretation is that of a magma intrusion. One possible explanation for the magma encounter at the IDDP-1 well is the existence of pathways or fissures connected to the magma chamber and intersected by the well. The MT response to these magma pathways is not discernible in the existing data, perhaps because this magma volume is below the threshold of resolvability. The electrical resistivity structure of the Hengill geothermal area also reveals characteristic features of a high temperature geothermal system with two low-resistivity layers. The nature of the uppermost low-resistivity layer and the increasing resistivity below it is attributed to hydrothermal mineral alteration, while the nature of the deep low-resistivity layer, centered over the northeast, is not yet well understood. The geothermal system in the northeast area appears to be shallower than the system manifested in the southwest. 3D MT inversions of Krafla and Hengill data sets show that knowledge of the subsurface electrical resistivity contributes substantially to a better understanding of complex geothermal systems.

Advantages of joint interpretation of P-P and P-SV seismic data in geothermal exploration

Conventional P-P seismic images of geothermal reservoirs are often of poor quality because P-P data tend to have a low signal-to-noise ratio across geothermal prospects. Fracture identification, fluid prediction, and imaging inside subsurface areas influenced by superheated fluids are some of the challenges facing the geothermal industry. We showed that multicomponent seismic technology is effective for addressing all of these challenges across geothermal reservoirs, even when P-P data are of low quality. Although multicomponent seismic technology has advantages in geothermal exploration, there are not many published examples of multicomponent seismic data being used to characterize geothermal reservoirs. We evaluated data examples that illustrate advantages of multicomponent seismic technology for imaging within and below zones having superheated fluids, estimating fracture attributes, analyzing reservoir trapping structures, differentiating lithologies, and predicting spatial distributions of pore fluids. All examples we tested are from the Wister geothermal field in Southern California.

Volcanological constraints on the post-emplacement zeolitisation of ignimbrites and geoarchaeological implications for Etruscan tomb construction (6th–3rd century B.C) in the Tufo Rosso a Scorie Nere, Vico Caldera, Central Italy

We examine the role of physical volcanological processes including eruption style (magmatic versus phreatomagmatic) as well as transport and depositional processes (pyroclastic fall versus pyroclastic flow) in promoting the ideal hydrologic conditions necessary for large scale, homogeneous, post-emplacement zeolitisation of ignimbrites, associated with caldera forming eruptions. We consider the Tufo Rosso a Scorie Nere (TRSN) of Vico Caldera (151 ka), in central Italy. The TRSN exhibits pervasive, homogenous alteration of high alkali tephriphonolitic and phonolitic glass to zeolite minerals (chabazite and phillipsite) in all regions of the study area and at all stratigraphic levels with the exception of the basal 1 m. Based on detailed lithological studies, we propose that a large geothermal field around the vent area was destroyed during the closing stages of the Sutri eruption. Subsequent incorporation and entrapment of superheated geothermal fluids into the ensuing pyroclastic flow during eruption column collapse greatly influenced the emplacement temperature and provided the necessary water required for post-emplacement zeolitisation of the TRSN. We suggest that the absence of zeolitisation at the base of the ignimbrite is directly related to transport conditions reflecting cooler regions in the lower portions of the deposit where the flow came into contact with the underlying substrate. We also consider the geoarchaeological implications of enhanced strength and cohesiveness provided by the zeolite rock framework on Etruscan tomb location and burial architecture in the Vico region. The TRSN contains literally hundreds of hypogeum-style Etruscan tombs at a number of sites across the study area. This study focuses on two sites in particular, the Norchia Necropoli and the San Guiliano Necropoli. Considering the enhanced mechanical properties of zeolitised ignimbrites we infer that physically the TRSN would still have been a relatively soft rock, suitable for the carving of tombs. However, we infer the increased strength and cohesiveness provided by the zeolite framework enhanced the conservation potential of these tombs, preserving them for over two thousand years.

Simulations of the explosive eruption of superheated fluids through deformable media

The sudden release of superheated fluids at depth can cause surface disturbances in the form of vents, mud volcanoes, or seafloor pockmarks. I have performed calculations with the Sage hydrocode (from Los Alamos and Science Applications International) of superheated venting in an idealised geometry, varying the pressure and velocity of hot fluid injected at depth. The simulations show several different patterns of propagation and fracturing in the deformable overburden. The simulations performed so far show, for different conditions, upward-propagating cylindrical pipes with hardened walls, narrowly diverging conical pipes, cone sheets, downward-propagating cracks, and funnel-shaped craters.

Depositional Facies and Diagenetic Alteration in a Relict Siliceous Hot-Spring Accumulation: Examples from Yellowstone National Park, U.S.A.

ABSTRACT Siliceous precipitates from portions of an 11-m-long core drilled through a relict Yellowstone hot-spring deposit provide valuable insights into the diagenetic facies in this hydrothermal environment. Most of the core consists of relatively low-temperature siliceous sinter containing abundant plant, diatom, and microbial fossilized remains derived from the distal debris apron and discharge channel/flowpath of the hot spring. A few intervals contain stromatolitic horizons analogous to modern, siliceous pool-margin and discharge channel/flowpath facies. Despite the abundance of silicified microbial remains (e.g., silicified stromatolitic horizons as well as individual filamentous microbes, diatoms), distinctive organic biomarkers are not preserved in the core. The apparent lack of distinctive organic biomarkers is attributable to pervasive diagenetic alteration in the presence of high-temperature, chemically reactive fluids. Numerous diagenetic features have been superimposed on the siliceous sinter, especially considering the relatively shallow depths of burial. The uppermost interval (0 to 1.2 m) consists of highly porous siliceous sinter (opal-A) and interbedded travertine. Amorphous manganese oxides and sparry calcite cements are present and are irregularly distributed throughout this interval. Below is a diagenetic facies (4.8 to 5.3 m) that consists of opal-CT and minor chalcedony. The most pervasive diagenetic alteration in the core is the 6.8 to 11.2 m depth interval, where abundant zeolites (mordenite, heulandite), bladed cristobalite lepispheres, chalcedony cements, and calcite veins are present. Judging by the assemblage of plant and diatom remains, most of this pervasive alteration is superimposed on relatively low-temperature siliceous sinters and is likely the result of migration of hot waters through this interval. The paragenesis of all these intervals is very complex, involving numerous episodes of mineral precipitation and dissolution. This diagenetic alteration is facilitated by the porous nature of the siliceous sinter, thermal convection of superheated fluids or steam, strongly oxidizing spring waters, and fluctuating hydrochemical regimes. Rapid dissolution and/or replacement of organic matter indicates that standard morphological means (e.g., petrographic identification of body fossils) may be the best method by which to identify that organisms were previously present in ancient hot-spring accumulations.

Measurements of gaseous isobaric specific heat capacity of alternative refrigerants

Abstract A new apparatus applying gas-flow calorimetry has been developed which enables to measure the isobaric specific heat, Cp, of superheated gaseous fluids with high accuracy at temperatures up to 473 K and pressures up to 10 MPa. The experimental uncertainties in temperature, pressure, and Cp measurements are estimated being not greater than ± 5 mK, ± 4 kPa and ± 0.26 %, respectively. Four Cp values of gaseous HCFC-22 have been measured and compared with available data measured by Bier et al. (1974) and Ernst and Busser (1970) for examining the reliability of the apparatus, and four Cp values of the new refrigerant HFC-134a have also been measured and discussed concerning the ideal-gas specific heat by comparing with Cp values derivrd from sound velocity measurements, spectroscopic measurements or existing equation of state for HFC-134a.

Particulate DNA in Smoker Fluids: Evidence for Existence of Microbial Populations in Hot Hydrothermal Systems

As part of an interdisciplinary study of hydrothermal vents on the Endeavour Segment of the Juan de Fuca Ridge, we used the submersible ALVIN to collect 57 fluid samples in titanium syringes and Go Flo Niskin bottles from 17 different hot vents (smokers and flanges) and their environs for the purpose of extracting particulate DNA. The relative purity of the vent fluids collected was determined by Mg content as an indicator of seawater entrainment. Particulate material concentrated from these samples was lysed enzymatically (enz) and by a combination of enzyme and French press treatment (fp). Concentrations of partially purified DNA recovered from these lysates were determined spectrofluorometrically by using the dye Hoechst 33258. Ambient seawater surrounding the vents was found to contain low DNA concentrations, 0.18 to 0.32 ng of DNA per ml (n = 4; mean(enz) = 0.23 +/- 0.05; mean(fp) = 0.26 +/- 0.05), while low-temperature vent samples yielded significantly higher concentrations of 0.37 to 2.12 ng of DNA per ml (n = 4; mean(enz) = 0.97 +/- 0.68; mean(fp) = 1.05 +/- 0.54). Although DNA recovery values from superheated (210 to 345 degrees C) flange samples (mean(enz) = 0.14 +/- 0.10; mean(fp) = 0.12 +/- 0.14) were not significantly different from ambient seawater values, most of the superheated (174 to 357 degrees C) smoker fluid samples contained particulate DNA in concentrations too high to be attributable to entrained seawater. Detailed sampling at one smoker site demonstrated not only the existence of significant levels of particulate DNA in the superheated smoker fluids but also the presence of an elevated microbial population in the buoyant plume 20 to 100 m above the smoker. These results underscore the heterogeneity of smoker environments within a given hydrothermal vent field and indicate that microorganisms exist in some superheated fluids.

Growth of ‘black smoker’ bacteria at temperatures of at least 250 °C

Complex communities of thermophilic bacteria have been cultured from the 350 °C waters emanating from sulphide chimneys, or ‘black smokers’, at 21 °N along the East Pacific Rise1. Several of the bacterial communities were shown to grow rapidly at 100 °C and atmospheric pressure, producing methane, hydrogen gas and carbon monoxide. These gases are found in superheated vent water, having previously been attributed to abiogenic reactions. Before concluding that these ‘black smoker’ bacteria actually contribute to the chemistry of the superheated hydrothermal fluids, it was necessary to test their ability to grow and produce gases at in situ vent temperatures and pressures. Here we report that a bacterial community originally cultured from 306 °C water is capable of chemolithotrophic growth in a titanium growth chamber under in situ vent pressure of 265 atm and at temperatures of at least 250 °C. (At 265 atm, seawater remains liquid at temperatures of at least 460 °C2.) Transmission electron microscopy of thin sections of bacteria cultured at 250 °C has revealed the presence of at least two morphologically distinct organisms.