Chemical composition of diffuse flow vent fluids collected from the Crab Spa site at East Pacific Rise during the AT26-10 oceanographic expedition, Jan. 2014 (Microbial Communities at Deep-Sea Vents project)

Dataset: vent chemical composition-Crab SpaThis dataset includes chemical composition (Cl, SO4, Na, K, Mg, and Ca concentrations) of diffuse flow vent fluids collected from the Crab Spa (9.8398º N, 104.2913º W) site at East Pacific Rise during the RV/Atlantic AT26-10 oceanographic expedition, Jan. 2014. Samples were collected at 2500 m depth by using isobaric gas-tight samplers (IGT, WHOI). Upon transfer onboard R/V Atlantis, the sampled diffuse flow fluids were incubated at 250 bars. Refer to the dataset https://www.bco-dmo.org/dataset/628993 for information regarding these incubations. For a complete list of measurements, refer to the supplemental document 'Field_names.pdf', and a full dataset description is included in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: http://www.bco-dmo.org/dataset/529026NSF Division of Ocean Sciences (NSF OCE) OCE-113660

Results from shipboard high-pressure incubations of diffuse flow vent fluids collected from the Crab Spa and Alvinella sites at East Pacific Rise during the AT26-10 expedition, Jan. 2014 (Microbial Communities at Deep-Sea Vents project)

Dataset: Incubation in diffuse flow vent fluids - Crab SpaThis dataset includes results from shipboard high-pressure incubations of diffuse flow vent fluids collected from the Crab Spa (9.8398º N, 104.2913º W) and Alvinella (9.8398º N, 104.2915º W) sites at East Pacific Rise during the AT26-10 oceanographic expedition in January 2014. Reported parameters include dates and time elapsed, flow rate, temperature, pressure, and pH, and concentrations of NO3, NH4, H2, H2S, CH4. For a complete list of measurements, refer to the supplemental document 'Field_names.pdf', and a full dataset description is included in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: http://www.bco-dmo.org/dataset/628993NSF Division of Ocean Sciences (NSF OCE) OCE-113660

Dynamic drivers of a shallow-water hydrothermal vent ecogeochemical system (Milos, Eastern Mediterranean)

Shallow-water hydrothermal vents share many characteristics with their deep-sea analogs. However, despite ease of access, much less is known about the dynamics of these systems. Here, we report on the spatial and temporal chemical variability of a shallow-water vent system at Paleochori Bay, Milos Island, Greece, and on the bacterial and archaeal diversity of associated sandy sediments. Our multi-analyte voltammetric profiles of dissolved O2 and hydrothermal tracers (e.g. Fe2+, FeSaq, Mn2+) on sediment cores taken along a transect in hydrothermally affected sediments indicate three different areas: the central vent area (highest temperature) with a deeper penetration of oxygen into the sediment, and a lack of dissolved Fe2+ and Mn2+; a middle area (0.5 m away) rich in dissolved Fe2+ and Mn2+ (exceeding 2 mM) and high free sulfide with potential for microbial sulfide oxidation as suggested by the presence of white mats at the sediment surface; and, finally, an outer rim area (1-1.5 m away) with lower concentrations of Fe2+ and Mn2+ and higher signals of FeSaq, indicating an aged hydrothermal fluid contribution. In addition, high-frequency temperature series and continuous in situ H2S measurements with voltammetric sensors over a 6-day time period at a distance 0.5 m away from the vent center showed substantial temporal variability in temperature (32 to 46 ºC ) and total sulfide (488 to 1329 �M) in the upper sediment layer. Analysis of these data suggests that tides, winds, and abrupt geodynamic events generate intermittent mixing conditions lasting for several hours to days. Despite substantial variability, the concentration of sulfide available for chemoautotrophic microbes remained high. These findings are consistent with the predominance of Epsilonproteobacteria in the hydrothermally influenced sediments Diversity and metagenomic analyses on sediments and biofilm collected along a transect from the center to the outer rim of the vent provide further insights on the metabolic activities and the environmental factors shaping these microbial communities. Both bacterial and archaeal diversity changed along the transect as well as with sediment depth, in line with the geochemical measurements. Beside the fact that it harbors an unexpected diversity of yet undescribed bacteria and archaea, this site is also a relevant model to investigate the link between ecological and abiotic dynamics in such instable hydrothermal environments. Our results provide evidence for the importance of transient geodynamic and hydrodynamic events in the dynamics and distribution of chemoautotrophic communities in the hydrothermally influenced sediments of Paleochori Bay

UV Irradiation and Near Infrared Characterization of Laboratory Mars Soil Analog Samples

The search for molecular biosignatures at the surface of Mars is complicated by an intense irradiation in the mid- and near-ultraviolet (UV) spectral range for several reasons: (i) many astrobiologically relevant molecules are electronically excited by efficient absorption of UV radiation and rapidly undergo photochemical reactions; (ii) even though the penetration depth of UV radiation is limited, aeolian erosion continually exposes fresh material to radiation; and (iii) UV irradiation generates strong oxidants such as perchlorates that can penetrate deep into soils and cause subsurface oxidative degradation of organics. As a consequence, it is crucial to investigate the effects of UV radiation on organic molecules embedded in mineral matrices mimicking the martian soil, in order to validate hypotheses about the nature of the organic compounds detected so far at the surface of Mars by the NASA Mars Science Laboratory’s (MSL) Curiosity rover, as well as organics that will be possibly found by the next rover missions Mars 2020 (NASA) and ExoMars 2022 (ESA-Roscosmos). In addition, studying the alteration of possible molecular biosignatures in the martian environment will help to redefine the molecular targets for life detection missions and devise suitable detection methods. Here we report the results of mid- and near-UV irradiation experiments of Mars soil analog samples obtained adsorbing relevant organic molecules on a clay mineral that is quite common on Mars, i.e. montmorillonite, doped with 1 wt% of magnesium perchlorate. Specifically, we chose to investigate the photostability of a plausible precursor of the chlorohydrocarbons detected on Mars by the Curiosity rover, namely phthalic acid, along with the biomarkers of extant life L-phenylalanine and L-glutamic acid, which are proteomic amino acids, and adenosine 5’-monophosphate, which is a nucleic acid component. We monitored the degradation of these molecules adsorbed on montmorillonite through in situ spectroscopic analysis, investigating the reflectance properties of the samples in the Near InfraRed (NIR) spectral region. Such spectroscopic characterization of molecular alteration products provides support for two upcoming robotic missions to Mars that will employ NIR spectroscopy to look for molecular biosignatures, through the instruments SuperCam on board Mars 2020, ISEM, Ma_Miss and MicrOmega on board ExoMars 2022

The old, unique C1 chondrite Flensburg - Insight into the first processes of aqueous alteration, brecciation, and the diversity of water-bearing parent bodies and lithologies

On September 12, 2019 at 12:49:48 (UT) a bolide was observed by hundreds of eye-witnesses from the Netherlands, Germany, Belgium, Denmark and the UK. One day later a small meteorite stone was found by accident in Flensburg. The presence of short-lived cosmogenic radionuclides with half-lives as short as 16 days proves the recent exposure of the found object to cosmic rays in space linking it clearly to the bolide event. An exceptionally short exposure time of ~5000 years was determined. The 24.5 g stone has a fresh black fusion crust, a low density of <2 g/cm^3, and a magnetic susceptibility of logX = 4.35 (X in 10^-9 m^3/kg). The rock consists of relict chondrules and clusters of sulfide and magnetite grains set in a fine-grained matrix. The most abundant phases are phyllosilicates. Carbonates (~3.9 vol.%) occur as calcites, dolomites, and a Na-rich phase. The relict chondrules (often surrounded by sulfide laths) are free of anhydrous silicates and contain abundant serpentine. Lithic clasts are also surrounded by similar sulfide laths partly intergrown with carbonates. 53^Mn-^53Cr ages of carbonates in Flensburg indicate that brecciation and contemporaneous formation of the pyrrhotite-carbonate intergrowths by hydrothermal activities occurred no later than 4564.6 +- 1.0 Ma (using the angrite D'Orbigny as the Mn-Cr age anchor). This corresponds to 2.6 +- 1.0 or 3.4 +- 1.0 Ma after formation of CAIs, depending on the exact absolute age of CAIs. This is the oldest dated evidence for brecciation and carbonate formation, which likely occurred during parent body growth and incipient heating due to decay of 26Al. In the three oxygen isotope diagram, Flensburg plots at the 16O-rich end of the CM chondrite field and in the transition field to CV-CK-CR chondrites. The mass-dependent Te isotopic composition of Flensburg is slightly different from mean CM chondrites and is most similar to those of the ungrouped C2 chondrite Tagish Lake. On the other hand, 50Ti and 54Cr isotope anomalies indicate that Flensburg is similar to CM chondrites, as do the ~10 wt.% H2O of the bulk material. Yet, the bulk Zn, Cu, and Pb concentrations are about 30% lower than those of mean CM chondrites. The He, Ne, and Ar isotopes of Flensburg show no solar wind contribution; its trapped noble gas signature is similar to that of CMs with a slightly lower concentration of 20Netr. Based on the bulk H, C, and N elemental abundances and isotopic compositions, Flensburg is unique among chondrites, because it has the lightest bulk H and N isotopic compositions of any type 1 or 2 chondrite investigated so far. Moreover, the number of soluble organic compounds in Flensburg is even lower than that of the brecciated CI chondrite Orgueil. The extraordinary significance of Flensburg is evident from the observation that it represents the oldest chondrite sample in which the contemporaneous episodes of aqueous alteration and brecciation have been preserved. The characterization of a large variety of carbonaceous chondrites with different alteration histories is important for interpreting returned samples from the OSIRIS-REx and Hayabusa 2 missions.This work is partly funded by the Deutsche Forschungs- gemeinschaft (DFG, German Research Foundation) – Project-ID 263649064 – TRR 170 (A.B., C.B., T.K.); this is TRR170 Publication No. 119. M.S. and C.M. thank the Swiss National Science Foundation (SNF) for support. The work of H.B. and M.S. has been in parts carried out within the framework of the NCCR PlanetS supported by SNF. D.H. thanks F. Langenhorst for support and access to the FIB-SEM and TEM facilities at FSU-IGW, which are funded by the DFG via grant LA830/14-1. D.F. (CIW) acknowledges the support of the NASA awards 80NSSC19K0559 and 80NSSC20K0344

Kinetics of H2–O2–H2O redox equilibria and formation of metastable H2O2 under low temperature hydrothermal conditions

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 75 (2011): 1594-1607, doi:10.1016/j.gca.2010.12.020.Hydrothermal experiments were conducted to evaluate the kinetics of H2(aq) oxidation in the homogeneous H2-O2-H2O system at conditions reflecting subsurface/near-seafloor hydrothermal environments (55-250 oC and 242-497 bar). The kinetics of the water-forming reaction that controls the fundamental equilibrium between dissolved H2(aq) and O2(aq), are expected to impose significant constraints on the redox gradients that develop when mixing occurs between oxygenated seawater and high- temperature anoxic vent fluid at near-seafloor conditions. Experimental data indicate that, indeed, the kinetics of H2(aq)-O2(aq) equilibrium become slower with decreasing temperature, allowing excess H2(aq) to remain in solution. Sluggish reaction rates of H2(aq) oxidation suggest that active microbial populations in near-seafloor and subsurface environments could potentially utilize both H2(aq) and O2(aq), even at temperatures lower than 40 oC due to H2(aq) persistence in the seawater/vent fluid mixtures. For these H2-O2 disequilibrium conditions, redox gradients along the seawater/hydrothermal fluid mixing interface are not sharp and microbially-mediated H2(aq) oxidation coupled with a lack of other electron acceptors (e.g. nitrate) could provide an important energy source available at low-temperature diffuse flow vent sites. More importantly, when H2(aq)-O2(aq) disequilibrium conditions apply, formation of metastable hydrogen peroxide is observed. The yield of H2O2(aq) synthesis appears to be enhanced under conditions of elevated H2(aq)/O2(aq) molar ratios that correspond to abundant H2(aq) concentrations. Formation of metastable H2O2 is expected to affect the distribution of dissolved organic carbon (DOC) owing to the existence of an additional strong oxidizing agent. Oxidation of magnetite and/or Fe++ by hydrogen peroxide could also induce formation of metastable hydroxyl radicals (•OH) through Fenton-type reactions, further broadening the implications of hydrogen peroxide in hydrothermal environments.This research was conducted with partial support from the NSF OCE-0752221 and the Geophysical Laboratory Postdoctoral Fellowship. We would also like to acknowledge contributions by the W.M. Keck Foundation and Shell towards supporting the hydrothermal lab at the Geophysical Lab. SMS acknowledges support from NSF OCE-0452333 and the Alfried-Krupp Wissenschaftskolleg Greifswald (Germany), while WES acknowledges support from NSF grants OCE-0549457 and OCE- 0813861

A Si-Cl geothermobarometer for the reaction zone of high-temperature, basaltic-hosted mid-ocean ridge hydrothermal systems

International audienceThe chemical composition of mid-ocean ridge hydrothermal vent fluids is thought to reflect conditions within a deep-seated reaction zone. Although temperature and pressure conditions within this region are key parameters that characterize the subseafloor hydrothermal regime and the cooling of mid-ocean ridges, they are poorly constrained. In this paper, we developed a model in which high-temperature, vapor-type (low-salinity) vent fluid silica (Si) and chlorine (Cl) concentrations can be used to define lines in pressure-temperature space whose intersection is used to estimate conditions at the top of the reaction zone, under the simplifying assumption that Si and Cl reflect a common point of equilibration. We apply this model to various basaltic-hosted mid-ocean ridge sites. Results suggest a minimal variation in inferred temperatures, ranging from 415 to 445°C. This lends support to the fluxibility model in which upwelling hydrothermal plumes rise at temperatures that maximize the energy flux. Quartz precipitation due to reequilibration during upflow tends to lower temperature and pressure estimates and can artificially indicate shallower transition from reaction to upflow zone. However, maximum equilibration pressures are site-dependent and compare well with depth to magma chamber imaged by seismic studies. This suggests that vapors circulate close to magma chambers and is difficult to reconcile with models in which mid-ocean ridge hydrothermal circulation occurs in two layers with a substantial layer of convecting brine. Accordingly, equilibration pressure predicted by our model can also be used to infer the depth of the magma chamber at sites where seismic data are not available but where vapor-like fluids have been collected and analyzed

Intramolecular hydrogen isotope exchange inside silicate melts – The effect of deuterium concentration

Tracing the deep geological water cycle requires knowledge of the hydrogen isotope systematics between and within hydrous materials. For quenched hydrous alkali-silicate melts, hydrogen NMR reveals a distinct heterogeneity in the distribution of stable hydrogen isotopes (D, H) within the silicate tetrahedral network, where deuterons concentrate strongly in network regions that are associated with alkali cations. Previous hydrogen NMR studies performed in the sodium tetrasilicate system (Na2O x 4SiO2, NS4) with a 1:1 D2O/H2O ratio showed on average 1300 ‰ deuterium enrichment in the alkali-associated network, but the effect on varying bulk D2O/H2O ratios on this intramolecular isotope effect remained unconstrained. Experiments in the hydrous sodium tetrasilicate system with 8 wt% bulk water and varying bulk D2O/H2O ratios were performed at 1400 °C and 1.5 GPa. It is found that both hydrogen isotopes preferably partition into the silicate network that is associated with alkali ions. The partitioning is always stronger for the deuterated than for the protonated hydrous species. The relative enrichment of deuterium over protium in the alkali-associated network, i.e., the intramolecular isotope effect, correlates positively with the D2O/H2O bulk ratio of the hydrous NS4 system. Modeled for natural deuterium abundance (D/H near 1.56 × 10−4), a 1.4-fold (c. 340 ‰) deuterium enrichment in the alkali-associated silicate network is predicted. The partitioning model further predicts a positive correlation between the bulk water content of the silicate melt and the intramolecular deuterium partitioning into the alkali-associated silicate network. Such heterogeneities may explain the magnitude and direction of hydrogen isotope fractionation in hydrous silicate melts coexisting with silicate-saturated fluids. As such, this intramolecular isotope effect appears to be an effective mechanism for deuterium separation, particularly in hydrous magmatic settings, such as subduction zones.ISSN:0009-2541ISSN:1872-683

Ecological succession of sulfur-oxidizing epsilon- And gammaproteobacteria during colonization of a shallow-water gas vent

In this study, we integrated geochemical measurements, microbial diversity surveys and physiological characterization of laboratory strains to investigate substrate-attached filamentous microbial biofilms at Tor Caldara, a shallow-water gas vent in the Tyrrhenian Sea. At this site, the venting gases are mainly composed of CO2 and H2S and the temperature at the emissions is the same as that of the surrounding water. To investigate the composition of the total and active fraction of the Tor Caldara biofilm communities, we collected established and newly formed filaments and we sequenced the 16S rRNA genes (DNA) and the 16S rRNA transcripts (cDNA). Chemoautotrophic sulfur-oxidizing members of the Gammaproteobacteria (predominantly Thiotrichales) dominate the active fraction of the established microbial filaments, while Epsilonproteobacteria (predominantly Sulfurovum spp.) are more prevalent in the young filaments. This indicates a succession of the two communities, possibly in response to age, sulfide and oxygen concentrations. Growth experiments with representative laboratory strains in sulfide gradient medium revealed that Sulfurovum riftiae (Epsilonproteobacteria) grew closer to the sulfide source than Thiomicrospira sp. (Gammaproteobacteria, Thiotrichales). Overall, our findings show that sulfur-oxidizing Epsilonproteobacteria are the dominant pioneer colonizers of the Tor Caldara biofilm communities and that Gammaproteobacteria become prevalent once the community is established. This succession pattern appears to be driven - among other factors - by the adaptation of Epsilon- and Gammaproteobacteria to different sulfide concentrations