No abstract

We report on integrated geomorphological, mineralogical, geochemical and biological investigations of the hydrothermal vent field located on the floor of the density-stratified acidic (pH ~ 5) crater of the Kolumbo shallow-submarine arc-volcano, near Santorini. Kolumbo features rare geodynamic setting at convergent boundaries, where arc-volcanism and seafloor hydrothermal activity are occurring in thinned continental crust. Special focus is given to unique enrichments of polymetallic spires in Sb and Tl (±Hg, As, Au, Ag, Zn) indicating a new hybrid seafloor analogue of epithermal-to-volcanic-hosted-massive-sulphide deposits. Iron microbial-mat analyses reveal dominating ferrihydrite-type phases, and high-proportion of microbial sequences akin to "Nitrosopumilus maritimus", a mesophilic Thaumarchaeota strain capable of chemoautotrophic growth on hydrothermal ammonia and CO2. Our findings highlight that acidic shallow-submarine hydrothermal vents nourish marine ecosystems in which nitrifying Archaea are important and suggest ferrihydrite-type Fe3+-(hydrated)-oxyhydroxides in associated low-temperature iron mats are formed by anaerobic Fe2+-oxidation, dependent on microbially produced nitrate.

Biofilms can provide a number of different ecological niches for microorganisms. Here, a multispecies biofilm was studied in which pyrite-oxidizing microbes are the primary producers. Its stability allowed not only detailed fluorescence in situ hybridization (FISH)-based characterization of the microbial population in different areas of the biofilm but also to integrate these results with oxygen and pH microsensor measurements conducted before. The O 2 concentration declined rapidly from the outside to the inside of the biofilm. Hence, part of the population lives under microoxic or anoxic conditions. Leptospirillum ferrooxidans strains dominate the microbial population but are only located in the oxic periphery of the snottite structure. Interestingly, archaea were identified only in the anoxic parts of the biofilm. The archaeal community consists mainly of so far uncultured Thermoplasmatales as well as novel ARMAN (Archaeal Richmond Mine Acidophilic Nanoorganism) species. Inductively coupled plasma analysis and X-ray absorption near edge structure spectra provide further insight in the biofilm characteristics but revealed no other major factors than oxygen affecting the distribution of bacteria and archaea. In addition to catalyzed reporter deposition FISH and oxygen microsensor measurements, microautoradiographic FISH was used to identify areas in which active CO 2 fixation takes place. Leptospirilla as well as acidithiobacilli were identified as primary producers. Fixation of gaseous CO 2 seems to proceed only in the outer rim of the snottite. Archaea inhabiting the snottite core do not seem to contribute to the primary production. This work gives insight in the ecological niches of acidophilic microorganisms and their role in a consortium. The data provided the basis for the enrichment of uncultured archaea.

Incorporation of sulphur in silicate glasses produced by reactions between melts and sulphur‐bearing sources at high temperatures was studied by X‐ray absorption near edge structure (XANES) spectroscopy at the sulphur K edge. Three types of syntheses were performed using sodium trisilicate, soda lime silicate, and float glass as starting materials: (i) controlled bubbling of glass melts with SO2 or SO2/O2 gas mixtures at ambient pressure, (ii) melting of glass powder containing various salts (Na2SO4, Na2SO3, Na2S) in excess to the expected solubility in the melt and (iii) fusion of glass powder in gold capsules at 1000°C and 100 MPa with an added amount of salts below the expected sulphur solubility. In some of the latter experiments water was introduced to vary the oxygen fugacity in the system. Sulphur concentrations in the glasses were determined by combustion and subsequent IR spectroscopy; water concentration in the glasses was measured by IR microspectroscopy. Bulk composition and homogeneity of glasses were checked by electron microprobe analyses. XANES spectra obtained at room temperature give evidence for incorporation of sulfate (S6+) and/or sulfide (monosulfide [S2−] and/or polysulfide [Sx2−]) in all glasses, depending on starting materials and run conditions. Clear evidence for sulfite (S4+) was not found in any of the spectra, implying that this sulphur species in glass products at room temperature is at or below the detection limit. We suggest that tetravalent sulphur (as SO2 or Na2SO3) disproportionates into sulfate and sulfide when being dissolved in simple silicate melts or during cooling of the glass melt.

No abstract