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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

Summary of δ57Fe isotope values for (A) EPR-4053-M3 (K Vent rubble), (B) EPR-4057-M2 (Bio9 Area massive sulfide), and (C) EPR-4059-M4 (extinct, off-axis chimney). Micro-drilling (MD), laser ablation (LA), pyrite, and oxyhydroxides sample characteristics are indicated in the legend.
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Figure 10: Summary of δ57Fe isotope values for (A) EPR-4053-M3 (K Vent rubble), (B) EPR-4057-M2 (Bio9 Area massive sulfide), and (C) EPR-4059-M4 (extinct, off-axis chimney). Micro-drilling (MD), laser ablation (LA), pyrite, and oxyhydroxides sample characteristics are indicated in the legend.

Mentions: The EPR chimney samples that exhibit complex interweaved layers of Fe(III), Si, and sulfide have a larger range of δ57Fe values relative to massive sulfides (e.g., EPR-4057-M2). When Fe oxyhydroxides occur as filling materials within the chimney wall or as outside layer crusts in association with Si-rich material, enrichments in both heavy and light Fe isotopes relative to pyrite are possible. The range of values δ57Fe is up to 6‰ which enlarges not only the range of Fe isotopes measured in hydrothermal vent environments (Rouxel et al., 2008a) but also in marine sediments (Severmann et al., 2006; Johnson et al., 2008; Rouxel et al., 2008b). In most cases, Fe-oxyhydroxides are enriched in light Fe isotopes relative to vent fluid sources (Figure 10).


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)

Summary of δ57Fe isotope values for (A) EPR-4053-M3 (K Vent rubble), (B) EPR-4057-M2 (Bio9 Area massive sulfide), and (C) EPR-4059-M4 (extinct, off-axis chimney). Micro-drilling (MD), laser ablation (LA), pyrite, and oxyhydroxides sample characteristics are indicated in the legend.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 10: Summary of δ57Fe isotope values for (A) EPR-4053-M3 (K Vent rubble), (B) EPR-4057-M2 (Bio9 Area massive sulfide), and (C) EPR-4059-M4 (extinct, off-axis chimney). Micro-drilling (MD), laser ablation (LA), pyrite, and oxyhydroxides sample characteristics are indicated in the legend.
Mentions: The EPR chimney samples that exhibit complex interweaved layers of Fe(III), Si, and sulfide have a larger range of δ57Fe values relative to massive sulfides (e.g., EPR-4057-M2). When Fe oxyhydroxides occur as filling materials within the chimney wall or as outside layer crusts in association with Si-rich material, enrichments in both heavy and light Fe isotopes relative to pyrite are possible. The range of values δ57Fe is up to 6‰ which enlarges not only the range of Fe isotopes measured in hydrothermal vent environments (Rouxel et al., 2008a) but also in marine sediments (Severmann et al., 2006; Johnson et al., 2008; Rouxel et al., 2008b). In most cases, Fe-oxyhydroxides are enriched in light Fe isotopes relative to vent fluid sources (Figure 10).

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