Pichler, Thomas
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Pichler, Thomas
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Pichler, Thomas
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Pichler, T.
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Item-typ:Veröffentlichung, Mineralogy of a natural As-rich hydrous ferric oxide coprecipitate formed by mixing of hydrothermal fluid and seawater: Implications regarding surface complexation and color banding in ferrihydrite deposits(De Gruyter, 2001-07-01); ; ; ; We characterized the most As-rich natural hydrous ferric oxide (HFO) material ever reported using powder X-ray diffraction (pXRD), transmission electron microscopy (TEM), X-ray fluorescence spectroscopy (XRF), light element analysis using gas chromatography (GC), visible-infrared (vis-IR) diffuse reflectivity, 57Fe Mössbauer spectroscopy, and superconducting quantum interference device (SQUID) magnetometry. We find that the natural As-HFO material is very similar to synthetic coprecipitated As-HFO materials, but is significantly different from all known natural and synthetic As-free HFO materials and ferrihydrite samples. The pXRD patterns show systematic differences with patterns for 2-line ferrihydrite, that are interpreted as evidence for significant populations of oxygen-coordinated Fe-As pairs. Observations by TEM, combined with energy dispersive spectroscopy (EDS) microanalysis, show agglomerations of nanophase primary particles and no evidence for other Fe- or As-bearing phases. Mössbauer spectroscopy shows octahedrally coordinated Fe3+, with a large fraction (~20%) of the octahedral Fe environments that are significantly distorted by the presence of As, compared to the Fe local environments in As-free ferrihydrite and HFO samples. The loss on ignition (LOI) is quantitatively consistent with OH + H2O, measured by GC, which, in turn, is consistent with ~1 nm diameter primary particles having all their surface cations (Fe3+, As5+, Si4+, C4+) coordinated on the free surface side by OH- and OH2. The banding into adjacent yellowish and reddish layers that occurs in the As-HFO deposits was studied by performing mineralogical analyses of the separated adjacent layers of two couplets of yellowish and reddish material. The yellowish samples were found not to contain secondary crystalline phases (as did the reddish samples, in small amounts) and to be relatively As-rich, C- and Si-poor. The observed anticorrelations between As and Si and between As and inorganic C suggest that natural HFOs, which usually contain significant molar amounts of Si, may not be as efficient at surface complexing As (and P) as their Si and C-free synthetic counterparts, unless formed by co-precipitation with the As (or P). The yellowish and reddish layers were also clearly resolved by both Mössbauer spectroscopy and magnetometry. Complexation of arsenate onto the HFO core was found to significantly increase the average quadrupole splitting (QS) obtained from Mössbauer spectroscopy by an amount that could not be explained by other chemical differences and that is consistent with an ~1 nm diameter particle size and somewhat smaller HFO core. The Munsell hue YR index (5-10 YR) was found to be strongly correlated to the average QS, thereby establishing that the color differences, corresponding to the measured shifts of the main visible band edge, are due to the local distortions in the [6]Fe3+ environments that are induced by As complexation, via their influence on the relevant ligand field transitions. SQUID magnetometry allows the following observations. (1) The superparamagnetic to superferromagnetic transitions occur at 25 K and lower in As-HFO, compared to 55 K in synthetic 2-line ferrihydrite, suggesting a smaller magnetic primary particle (or core) size for As-HFO and inter-particle magnetic interaction reduction by surface complexed As, Si, and C. (2) The ratio of supermoment magnitude to magnetic particle size (m2/n, where m is the net number of Fe3+ atomic moments per supermoment and n is the number of Fe3+ cations per particle or HFO core) decreases with increasing As content in the sequence synthetic-HFO > reddish-As-HFO > yellowish-As-HFO. (3) The magnetic susceptibility magnitudes for As-HFO and synthetic 2-line ferrihydrite differ by a factor of 10 and suggest different supermoment formation mechanisms (m2/n < 1 vs. m2/n > 1, respectively) related to differences in intra-particle cationic and anionic disorder and magnetic particle size.Wissenschaftlicher ArtikelBand:86Heft:7-865 87 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Stable and radiogenic isotopes as tracers for the origin, mixing and subsurface history of fluids in submarine shallow-water hydrothermal systemsThe shallow-water hydrothermal system in Tutum Bay on the west side of Ambitle Island, Papua New Guinea provides us with an exceptional opportunity to study isotope systematics in a near shore setting. Compared to seawater, the hydrothermal fluids in Tutum Bay have lower values for δD, δ18O, δ13C, and 87Sr and higher values for 3H, δ34S(SO4) and δ18O(SO4). The δ18O and δD records for vents 1 and 4 indicate that fluid compositions remained stable over an extended period. Interpretation of isotope data clearly demonstrates the predominantly meteoric origin of Tutum Bay hydrothermal fluids, despite their location in a marine environment. δ18O and δD values are identical to mean average annual precipitation in eastern Papua New Guinea. The hypothesis that these fluids are a simple product of mixing between seawater and onshore hydrothermal fluids from the Waramung (W-1) and Kapkai (W-2) thermal areas has been rejected, because the observed δ37Cl, 3H, δ34S(SO4) and δ18O(SO4) values cannot be explained by a simple mixing model. The application of δ18O(SO4) and δ13C thermometers in combination with 3H values corroborates the three-step model of Pichler et al. [Pichler, T., Veizer, J., Hall, G.E.M., 1999. The chemical composition of shallow-water hydrothermal fluids in Tutum Bay, Ambitle Island, Papua New Guinea and their effect on ambient seawater. Marine Chemistry 64 (3) 229–252], where (1) phase separation in the deep reservoir beneath Ambitle Island produces a high temperature vapor that rises upward and subsequently reacts with cooler ground water to form a low pH, CO2-rich water of approximately 150–160 °C, (2) caused by the steep topography, this CO2-rich fluid moves laterally towards the margin of the hydrothermal system where it mixes with the marginal upflow of the deep reservoir fluid. This produces a dilute chloride water of approximately 165 °C, and (3) possibly the entrainment of minor amounts of ground or seawater during its final ascent.Wissenschaftlicher ArtikelBand:139Heft:3-4428 57 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Geochemistry of Champagne Hot Springs shallow hydrothermal vent field and associated sediments, Dominica, Lesser AntillesThe Champagne Hot Springs (CHS) shallow submarine hydrothermal system is located along the submerged flank of the Plat Pays volcanic system on the southwest section of the island of Dominica, Lesser Antilles. We have conducted a detailed geochemical study of the hydrothermal system, with the objectives to investigate the source of the hydrothermal fluids and gases, their effect on sediment and precipitate chemistry, as well as comparing the submarine vent chemistry with nearby on-land hydrothermal vents. Finally, we compare our findings to previous preliminary data from CHS, and compare sediment chemistry to that of average Caribbean sediments. We also report on a newly discovered area of submarine hydrothermal venting, located approximately 40 m to the north of CHS. This area consists of hydrothermally altered areas of sand that contain abundant coatings of hydrous ferric oxides (HFO) on sediment grains. Geochemical and mineralogical analyses of vent waters, pore waters, gases, sediments and precipitates reveal that the vent fluids consist of a mixture of entrained seawater and meteorically derived hydrothermal fluid in varying proportions. Vent fluids are depleted in Br−, SO42−, Cl−, Na+, K+, and Sr2+ relative to ambient seawater. These species are all positively correlated with Mg2+, which is also depleted relative to seawater. Boron, Fe, As, Sb, Mn, Si and Li are all enriched relative to ambient seawater. Pore waters in the hydrothermally altered sand patches have essentially the same chemistry. Mixing between Fe2+ rich vent fluids and seawater causes rapid oxidation of Fe2+ to insoluble Fe3+ and leads to precipitation of HFO at the vent site and subsequent formation of hydrothermally altered sand patches. The elevated concentrations of As and Sb in the precipitates and sediments relative to average Caribbean seafloor sediments reflect adsorption by HFO. Gas samples from the vent site are typical arc-type gases and have both meteoric and magmatic signatures.Wissenschaftlicher ArtikelBand:224Heft:1-361 53 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Energy sources for chemolithotrophs in an arsenic- and iron-rich shallow-sea hydrothermal systemThe hydrothermally influenced sediments of Tutum Bay, Ambitle Island, Papua New Guinea, are ideal for investigating the chemolithotrophic activities of micro-organisms involved in arsenic cycling because hydrothermal vents there expel fluids with arsenite (AsIII) concentrations as high as 950 μg L−1. These hot (99 °C), slightly acidic (pH ∼6), chemically reduced, shallow-sea vent fluids mix with colder, oxidized seawater to create steep gradients in temperature, pH, and concentrations of As, N, Fe, and S redox species. Near the vents, iron oxyhydroxides precipitate with up to 6.2 wt% arsenate (AsV). Here, chemical analyses of sediment porewaters from 10 sites along a 300-m transect were combined with standard Gibbs energies to evaluate the energy yields (−ΔGr) from 19 potential chemolithotrophic metabolisms, including AsV reduction, AsIII oxidation, FeIII reduction, and FeII oxidation reactions. The 19 reactions yielded 2–94 kJ mol−1 e−, with aerobic oxidation of sulphide and arsenite the two most exergonic reactions. Although anaerobic AsV reduction and FeIII reduction were among the least exergonic reactions investigated, they are still potential net metabolisms. Gibbs energies of the arsenic redox reactions generally correlate linearly with pH, increasing with increasing pH for AsIII oxidation and decreasing with increasing pH for AsV reduction. The calculated exergonic energy yields suggest that micro-organisms could exploit diverse energy sources in Tutum Bay, and examples of micro-organisms known to use these chemolithotrophic metabolic strategies are discussed. Energy modeling of redox reactions can help target sampling sites for future microbial collection and cultivation studies.Wissenschaftlicher ArtikelBand:9Heft:571 175 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Amorphous arsenic sulfide nanoparticles in a shallow water hydrothermal system(Elsevier Science, 2019-04-23); ; ; ; Hydrothermal fluids can contain trace elements such as arsenic (As), which are toxic to surrounding biota. In these kind of fluids, the bioavailability and biotransformation of As have been investigated but so far the ratio of total soluble As (<200 nm) versus the amount of As contained in a nanoparticulate phase has not been reported. Here, for the first time, the presence of As in the nanoparticulate fraction (between 200 and 20 nm) is described for arsenic-rich hydrothermal fluids in a marine shallow-water hydrothermal system. Samples of diffusively venting hydrothermal fluids, pore-water and seawater were collected in the hydrothermal system located in Paleochori Bay, Milos Island (Greece), and the fraction between 200 and 20 nm (As200-20) was studied. Up to 38% of the soluble arsenic was present within the As200-20 fraction in pore fluids, 10 to 20% in hydrothermal fluids and 5% in seawater. Identification and characterization of particles in hydrothermal fluid, pore-water and seawater was performed by scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM) with selected area electron diffraction (SAED) and dynamic light scattering (DLS). The particles are of spherical morphology with a polydisperse size distribution (PDI: 0.37) and diameters close to 100 nm. EDX studies confirmed a chemical composition rich in As and S. The SAED pattern revealed absence of a crystal phase indicating the presence of an amorphous arsenic sulfide material. These results bring into discussion the role of the nanoparticulate fraction for As dispersion, bioavailability, and potentially harmful effects in marine coastal ecosystems.Wissenschaftlicher ArtikelBand:211100 155 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Submarine groundwater discharge within a landslide scar at the French Mediterranean coast(Elsevier Science, 2017-11-05); ; ; ; Submarine groundwater discharge (SGD), the flow of fresh and saline groundwater from the seabed into the coastal ocean, has been intensively investigated in the recent years. This research has usually been restricted to shallow water and intertidal areas, whereas knowledge about groundwater seepage in deeper water is mainly limited to point sources from karstic aquifers. In this study we observed submarine groundwater seepage and a subterranean estuary in sediments at water depths of 20–44 m located within the Ligurian Margin, western Mediterranean Sea. Here, a catastrophic submarine landslide occurred near the Nice airport (French Ligurian coast) in the fall of 1979 after a period of heavy rainfall. During two research cruises, gravity cores were recovered in and around the area of the landslide scar. Pore water samples collected from sediment cores indicated sediments containing freshwater within the landslide scar. Pore water profiles of selected ions, such as chloride, ammonium, manganese, sulfate and barium were used to assess transport and reaction processes within the sediment. A 1-dimensional transport model indicates in most cores upward pore water velocities of 2.3–8.8 cm yr−1. This study shows that submarine groundwater seepage along the French Mediterranean coastline can occur at water depths reaching 44 m.Wissenschaftlicher ArtikelBand:19853 35 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Cadmium in soils and groundwater: A reviewCadmium (Cd) is a non-essential trace element that is widely distributed in the environment. Both geogenic and anthropogenic sources can elevate Cd concentrations in soils and groundwater, which are important for maintaining healthy supplies of food and safe drinking water. Elevated Cd doses are carcinogenic to humans. The WHO Guidelines for Drinking-Water Quality recommend a guideline value for Cd of 3 μg/L. Important anthropogenic Cd sources include mining, atmospheric deposition of combustion emissions, and the use of Cd-containing fertilizers. We document several cases of Cd pollution in soil and groundwater based on worldwide accounts. Besides anthropogenic Cd sources, Cd is also incorporated into sulfides, carbonates, and phosphorites resulting in elevated Cd concentrations in associated rock types. The crustal median Cd content is 0.2 mg/kg. In soils, Cd occurs at concentrations of 0.01 to 1 mg/kg with a worldwide mean of 0.36 mg/kg. Weathering can lead to Cd concentrations up to 5 μg/L in soil water and up to 1 μg/L in groundwater. In aqueous solutions, Cd generally occurs as the divalent Cd2+ and it is mobilized mainly in oxic, acidic conditions. Cadmium sorption is enhanced by the presence of high amounts of hydrous oxides, clay minerals, and organic matter, and its mobility is further influenced by pH, the redox state, and ionic strength of the solution. However, Cd can remain in solution as water-soluble complexes with anions, such as CdCl+ and Cd(SO4)22-, and dissolved organic matter while sorption and precipitation decrease the aqueous concentration of most other heavy metals. As a consequence, Cd is one of the most mobile heavy metals in the environment. The elevated mobilization potential, e.g., through competition and ligand induced desorption, is the reason for faster Cd release from soil into groundwater than other heavy metals. The goal of this study was to present a broad overview of the origin and concentration of Cd in groundwater, and its reaction pathways in aquatic environments. To gain an overview of the hydrochemical behavior of Cd, cases of Cd pollution in soil and groundwater, studies investigating Cd release, and information about the legal framework were compiled.Wissenschaftlicher ArtikelBand:108162 465 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Precipitation of Fe(III) oxyhydroxide deposits from shallow-water hydrothermal fluids in Tutum Bay, Ambitle Island, Papua New GuineaPrevious research on sea floor Fe(III) oxyhydroxide deposits has focused primarily on deep-sea, hydrothermal systems found along volcanically active portions of the mid-ocean ridges and on hydrogenetic deposits formed in deep basins and along continental shelves. There is, however, not much known about their formation in shallow-water settings associated with volcanic islands. The hydrothermal system at Ambitle Island, Papua New Guinea provides an excellent opportunity to study the formation of Fe(III) oxyhydroxides in a shallow-water setting. Precipitation from the hydrothermal solution is caused by mixing with seawater. Based on a 87Sr/86Sr mixing model, the calculated minimum and maximum seawater fractions are approximately 11 and 57%, respectively. Thus, precipitation of Tutum Bay Fe(III) oxyhydroxides takes place at a temperature range between approximately 60 and 93°C. The chemical composition shows low Mn contents (Fe/Mn>600), and elements that are usually enriched in Fe(III) oxyhydroxides, such as Co and V are below crustal abundance and well below their concentrations in island-arc volcanics. Arsenic concentrations, on the other hand, are by two orders of magnitude higher than those in other marine deposits. Rare earth element (REE) concentrations reflect their concentration in the hydrothermal fluids rather than seawater. The crystallinity of the deposits increases with age, as protoferrihydrite is apparently altered to Fe-smectite and hematite, and As-bearing minerals are formed. Contact with seawater, and therefore oxidizing conditions, seems to be the factor increasing the crystallinity.Wissenschaftlicher ArtikelBand:162Heft:178 56 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Low-temperature alteration of dredged volcanics from the Southern Chile Ridge: additional information about early stages of seafloor weatheringA suite of submarine volcanic rocks from the Southern Chile Ridge has been examined in order to investigate the early stages of low temperature alteration. Alteration in these samples proceeded as follows: (1) Fe-staining on sample surface and along fractures, (2) filling of vesicles with secondary material, (3) breakdown of glassy matrix, (4) breakdown of microcrystalline matrix, and (5) breakdown and replacement of olivine. Plagioclase and pyroxene were sometimes found to be slightly altered along internal fissures. Secondary or alteration phases generally showed high K (3–5 wt.%), Fe (30–70 wt.%) and low Al (<2 wt.%) contents. The most common secondary minerals were Fe-oxyhydroxides, celadonite/Fe-oxyhydroxide (a mixture between celadonite and Fe-oxyhydroxide) and saponite. The formation of secondary minerals is controlled by the oxidation state which is a direct result of seawater to rock ratio. Fe-oxyhydroxides and celadonite/Fe-oxyhydroxide form during oxidative diagenesis, whereas saponite forms during non-oxidative diagenesis. The final alteration products, however, are controlled by external factors, e.g., sedimentation rate or formation of a manganese crust. Ca has been consistently removed, Mg has been added to some rocks and lost from others, and Si has either been removed or remained unaffected. Fe and H2O increases are accompanied by an increase in Fe3+/Fe2+. Wherever increases in K, Rb and Cs were documented, the enrichments are consistently in the order Cs>Rb>K. During initial stages of alteration the behavior of some trace elements such as rare-earth elements (REE), Ba, Zr, Hf, Ta, Nb, and Mo are solely controlled by the precipitation of Mn-rich Fe-oxyhydroxides. The preferred incorporation of Ce into Mn-rich Fe-oxyhydroxides may be a principal factor explaining the Ce depletion in seawater. We conclude that the earliest stages of submarine weathering are controlled by Eh and pH gradients between the rock and seawater. In the absence of a buffer, oxidation of ferrous iron causes a decrease in solution pH.Wissenschaftlicher ArtikelBand:159Heft:1-467 43 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Arsenic bioaccumulation and biotransformation in deep-sea hydrothermal vent organisms from the PACMANUS hydrothermal field, Manus Basin, Papua New Guinea(Elsevier Science, 2016-11); ; ; ; Hydrothermal vents are often enriched in arsenic, and organisms living in these environments may accumulate high concentrations of this and other trace elements. However, very little research to date has focused on understanding arsenic bioaccumulation and biotransformation in marine organisms at deep-sea vent areas; none to date have focused organisms from back-arc spreading centers. We present for the first time concentration and speciation data for As in vent biota from several hydrothermal vent fields in the eastern Manus basin, a back-arc basin vent field located in the Bismark Sea, western Pacific Ocean. The gastropods Alviniconcha hessleri and Ifremeria nautilei, and the mussel Bathymodiolus manusensis were collected from diffuse venting areas where pH was slightly lower (6.2–6.8), and temperature (26.8–10.5 °C) and arsenic concentrations (169.5–44.0 nM) were higher than seawater. In the tissues of these organisms, the highest total measured As concentrations were in the gills of A. hessleri (5580 mg kg−1), with 721 mg kg−1 and 43 mg kg−1 in digestive gland and muscle, respectively. I. nautilei contained 118 mg kg−1 in the gill, 108 mg kg−1 in the digestive gland and 22 mg kg−1 in the muscle. B. manusensis contained 15.7 mg kg−1 in the digestive gland, followed by 9.8 mg kg-1 and 4.5 mg kg-1 in its gill and muscle tissue, respectively. We interpret the decreasing overall total concentrations in each organism as a function of distance from the source of hydrothermally derived As. The high concentration of arsenic in A. hessleri gills may be associated with elemental sulfur known to occur in this organism as a result of symbiotic microorganisms. Arsenic extracted from freeze-dried A. hessleri tissue was dominated by AsIII and AsV in the digestive gland (82% and 16%, respectively) and gills (97% AsIII, 2.3% AsV), with only 1.8% and 0.2% arsenobetaine (As-Bet) in the digestive gland and gills, respectively. However, the muscle contained substantial amounts of As-Bet (42% As-Bet compared to 48% AsIII and 10% AsV), suggesting As-Bet is a metabolite. Trace arsenosugar (SO4-sug) was observed in digestive gland and gills only. The other snail, I. nautilei, was also dominated by AsIII and AsV in digestive glands (82, 10%) and gills (80, 10%), with 6–9% As-Bet, but its muscle contained 62% As-Bet and 32% AsIII, with 7% trimethylarsoniopropionate (TMAP). Trace dimethylarsinic acid (DMAV) was observed in its gills, and trace TMAP and arsenocholine (AC) was observed in digestive glands. The mussel B. manusensis was dominated by As-Bet in all three tissue types. Digestive gland and gills contained ~22% AsIII, 5–10% AsV, 20–25% DMAV, along with some TMAP and tetramethylarsonium ion (TETRA). However, the muscle contained significantly more As-Bet (91.6%), with the only other species being AsIII (8.4%). Unfortunately, as is often the case in bioaccumulation and biotransformation studies, extraction efficiencies were low, limiting any rigorous interpretation of arsenic biotransformation patterns. Through process of elimination, we suggest that arsenosugars may be synthesized by H2S-oxidizing chemotrophic microbial mats, ultimately leading to the syntheses of As-Bet within vent organisms. However, because As-sugs rarely occur in deep-sea vent organisms, As-Bet, as well as TMAP, AC, and TETRA could also potentially be synthesized directly by the “Edmonds” pathway, the proposed arseno-analog to amino acid formation, without the necessity for arsenosugar formation as an intermediate. Future research should endeavor for more comprehensive extraction of organoarsenicals.Wissenschaftlicher ArtikelBand:11748 75