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Iron Transformation Pathways and Redox Micro-Environments in Seafloor Sulfide-Mineral Deposits: Spatially Resolved Fe XAS and δ(57/54)Fe Observations.

Toner BM, Rouxel OJ, Santelli CM, Bach W, Edwards KJ - Front Microbiol (2016)

Bottom Line: Pathway 2 is also consistent with zones of mixing but involves precipitation of sulfide minerals from Fe(II)aq generated by Fe(III) reduction.The Fe mineralogy and isotope data do not support or refute a unique biological role in sulfide alteration.These micro-environments likely support redox cycling of Fe and S and are consistent with culture-dependent and -independent assessments of microbial physiology and genetic diversity of hydrothermal sulfide deposits.

View Article: PubMed Central - PubMed

Affiliation: Département des Ressources Physiques et Écosystèmes de Fond de Mer, Water, and Climate, University of Minnesota-Twin Cities St. Paul, MN, USA.

ABSTRACT
Hydrothermal sulfide chimneys located along the global system of oceanic spreading centers are habitats for microbial life during active venting. Hydrothermally extinct, or inactive, sulfide deposits also host microbial communities at globally distributed sites. The main goal of this study is to describe Fe transformation pathways, through precipitation and oxidation-reduction (redox) reactions, and examine transformation products for signatures of biological activity using Fe mineralogy and stable isotope approaches. The study includes active and inactive sulfides from the East Pacific Rise 9°50'N vent field. First, the mineralogy of Fe(III)-bearing precipitates is investigated using microprobe X-ray absorption spectroscopy (μXAS) and X-ray diffraction (μXRD). Second, laser-ablation (LA) and micro-drilling (MD) are used to obtain spatially-resolved Fe stable isotope analysis by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS). Eight Fe-bearing minerals representing three mineralogical classes are present in the samples: oxyhydroxides, secondary phyllosilicates, and sulfides. For Fe oxyhydroxides within chimney walls and layers of Si-rich material, enrichments in both heavy and light Fe isotopes relative to pyrite are observed, yielding a range of δ(57)Fe values up to 6‰. Overall, several pathways for Fe transformation are observed. Pathway 1 is characterized by precipitation of primary sulfide minerals from Fe(II)aq-rich fluids in zones of mixing between vent fluids and seawater. Pathway 2 is also consistent with zones of mixing but involves precipitation of sulfide minerals from Fe(II)aq generated by Fe(III) reduction. Pathway 3 is direct oxidation of Fe(II) aq from hydrothermal fluids to form Fe(III) precipitates. Finally, Pathway 4 involves oxidative alteration of pre-existing sulfide minerals to form Fe(III). The Fe mineralogy and isotope data do not support or refute a unique biological role in sulfide alteration. The findings reveal a dynamic range of Fe transformation pathways consistent with a continuum of micro-environments having variable redox conditions. These micro-environments likely support redox cycling of Fe and S and are consistent with culture-dependent and -independent assessments of microbial physiology and genetic diversity of hydrothermal sulfide deposits.

No MeSH data available.


Related in: MedlinePlus

Distribution of Fe, S, and V in massive sulfide deposits near Bio9 Vent. X-ray fluorescence maps for (A) EPR-4057-M2, and (B) red-green-blue (Fe-S-V) distribution for EPR-4059-M3. White numbers indicate locations for Fe X-ray absorption near edge structure (XANES) (Table S3) or extended X-ray absorption fine structure (EXAFS) (Table S4) data collection.
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Figure 3: Distribution of Fe, S, and V in massive sulfide deposits near Bio9 Vent. X-ray fluorescence maps for (A) EPR-4057-M2, and (B) red-green-blue (Fe-S-V) distribution for EPR-4059-M3. White numbers indicate locations for Fe X-ray absorption near edge structure (XANES) (Table S3) or extended X-ray absorption fine structure (EXAFS) (Table S4) data collection.

Mentions: Our sample set includes two massive sulfide deposits in the vicinity of Bio9 Vent (EPR-4057-M2 and EPR-4059-M3; Figures S1C,D). Both deposits exhibit Fe-rich and S-depleted zones at the seawater exposed surfaces with low (or undetectable) Si (Figure 3). The Fe XANES data for EPR-4057-M2 are dominated by the Fe(III) oxyhydroxide goethite with lesser contributions of a biogenic-like Fe oxyhydroxide signature (Table S3). The goethite phase assignment is supported by Fe EXAFS (Table S4) and micro-probe X-ray diffraction (Figure S7). One Fe XANES location is consistent with the Fe(III) oxyhydroxide lepidocrocite (spot 7). Where Fe XANES and EXAFS observations overlap for this sample, the observations are in agreement (Table S4). The Fe XANES data for the seawater exposed portion of massive sulfide EPR-4059-M3 reveal heterogeneous Fe-bearing mineralogy: consistent with 2-line ferrihydrite, goethite, akaganeite, and secondary phyllosilicates (“clay” minerals; Table S3). Despite the complexity in Fe-bearing phases, the Fe-rich and S-depleted phases are predominantly Fe(III).


Iron Transformation Pathways and Redox Micro-Environments in Seafloor Sulfide-Mineral Deposits: Spatially Resolved Fe XAS and δ(57/54)Fe Observations.

Toner BM, Rouxel OJ, Santelli CM, Bach W, Edwards KJ - Front Microbiol (2016)

Distribution of Fe, S, and V in massive sulfide deposits near Bio9 Vent. X-ray fluorescence maps for (A) EPR-4057-M2, and (B) red-green-blue (Fe-S-V) distribution for EPR-4059-M3. White numbers indicate locations for Fe X-ray absorption near edge structure (XANES) (Table S3) or extended X-ray absorption fine structure (EXAFS) (Table S4) data collection.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4862312&req=5

Figure 3: Distribution of Fe, S, and V in massive sulfide deposits near Bio9 Vent. X-ray fluorescence maps for (A) EPR-4057-M2, and (B) red-green-blue (Fe-S-V) distribution for EPR-4059-M3. White numbers indicate locations for Fe X-ray absorption near edge structure (XANES) (Table S3) or extended X-ray absorption fine structure (EXAFS) (Table S4) data collection.
Mentions: Our sample set includes two massive sulfide deposits in the vicinity of Bio9 Vent (EPR-4057-M2 and EPR-4059-M3; Figures S1C,D). Both deposits exhibit Fe-rich and S-depleted zones at the seawater exposed surfaces with low (or undetectable) Si (Figure 3). The Fe XANES data for EPR-4057-M2 are dominated by the Fe(III) oxyhydroxide goethite with lesser contributions of a biogenic-like Fe oxyhydroxide signature (Table S3). The goethite phase assignment is supported by Fe EXAFS (Table S4) and micro-probe X-ray diffraction (Figure S7). One Fe XANES location is consistent with the Fe(III) oxyhydroxide lepidocrocite (spot 7). Where Fe XANES and EXAFS observations overlap for this sample, the observations are in agreement (Table S4). The Fe XANES data for the seawater exposed portion of massive sulfide EPR-4059-M3 reveal heterogeneous Fe-bearing mineralogy: consistent with 2-line ferrihydrite, goethite, akaganeite, and secondary phyllosilicates (“clay” minerals; Table S3). Despite the complexity in Fe-bearing phases, the Fe-rich and S-depleted phases are predominantly Fe(III).

Bottom Line: Pathway 2 is also consistent with zones of mixing but involves precipitation of sulfide minerals from Fe(II)aq generated by Fe(III) reduction.The Fe mineralogy and isotope data do not support or refute a unique biological role in sulfide alteration.These micro-environments likely support redox cycling of Fe and S and are consistent with culture-dependent and -independent assessments of microbial physiology and genetic diversity of hydrothermal sulfide deposits.

View Article: PubMed Central - PubMed

Affiliation: Département des Ressources Physiques et Écosystèmes de Fond de Mer, Water, and Climate, University of Minnesota-Twin Cities St. Paul, MN, USA.

ABSTRACT
Hydrothermal sulfide chimneys located along the global system of oceanic spreading centers are habitats for microbial life during active venting. Hydrothermally extinct, or inactive, sulfide deposits also host microbial communities at globally distributed sites. The main goal of this study is to describe Fe transformation pathways, through precipitation and oxidation-reduction (redox) reactions, and examine transformation products for signatures of biological activity using Fe mineralogy and stable isotope approaches. The study includes active and inactive sulfides from the East Pacific Rise 9°50'N vent field. First, the mineralogy of Fe(III)-bearing precipitates is investigated using microprobe X-ray absorption spectroscopy (μXAS) and X-ray diffraction (μXRD). Second, laser-ablation (LA) and micro-drilling (MD) are used to obtain spatially-resolved Fe stable isotope analysis by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS). Eight Fe-bearing minerals representing three mineralogical classes are present in the samples: oxyhydroxides, secondary phyllosilicates, and sulfides. For Fe oxyhydroxides within chimney walls and layers of Si-rich material, enrichments in both heavy and light Fe isotopes relative to pyrite are observed, yielding a range of δ(57)Fe values up to 6‰. Overall, several pathways for Fe transformation are observed. Pathway 1 is characterized by precipitation of primary sulfide minerals from Fe(II)aq-rich fluids in zones of mixing between vent fluids and seawater. Pathway 2 is also consistent with zones of mixing but involves precipitation of sulfide minerals from Fe(II)aq generated by Fe(III) reduction. Pathway 3 is direct oxidation of Fe(II) aq from hydrothermal fluids to form Fe(III) precipitates. Finally, Pathway 4 involves oxidative alteration of pre-existing sulfide minerals to form Fe(III). The Fe mineralogy and isotope data do not support or refute a unique biological role in sulfide alteration. The findings reveal a dynamic range of Fe transformation pathways consistent with a continuum of micro-environments having variable redox conditions. These micro-environments likely support redox cycling of Fe and S and are consistent with culture-dependent and -independent assessments of microbial physiology and genetic diversity of hydrothermal sulfide deposits.

No MeSH data available.


Related in: MedlinePlus