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Mineralogy of iron microbial mats from loihi seamount.

Toner BM, Berquó TS, Michel FM, Sorensen JV, Templeton AS, Edwards KJ - Front Microbiol (2012)

Bottom Line: Disorder in the nanostructured Fe-bearing phases results in limited intermediate-range structural order: less than that of standard two-line ferrihydrite (Fh), except for the Pohaku site.The presence of coated particles explains the small CSD for the mat minerals, as well as the stability of the minerals over time and against heating.The mineral properties observed here provide a starting point from which progressively older and more extensively altered Fe deposits may be examined, with the ultimate goal of improved interpretation of past biogeochemical conditions and diagenetic processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Soil, Water, and Climate, University of Minnesota-Twin Cities St. Paul, MN, USA.

ABSTRACT
Extensive mats of Fe oxyhydroxides and associated Fe-oxidizing microbial organisms form in diverse geochemical settings - freshwater seeps to deep-sea vents - where ever opposing Fe(II)-oxygen gradients prevail. The mineralogy, reactivity, and structural transformations of Fe oxyhydroxides precipitated from submarine hydrothermal fluids within microbial mats remains elusive in active and fossil systems. In response, a study of Fe microbial mat formation at the Loihi Seamount was conducted to describe the physical and chemical characteristics of Fe-phases using extended X-ray absorption fine structure spectroscopy, powder X-ray diffraction, synchrotron radiation X-ray total scattering, low-temperature magnetic measurements, and Mössbauer spectroscopy. Particle sizes of 3.5-4.6 nm were estimated from magnetism data, and coherent scattering domain (CSD) sizes as small as 1.6 nm are indicated by pair distribution function (PDF) analysis. Disorder in the nanostructured Fe-bearing phases results in limited intermediate-range structural order: less than that of standard two-line ferrihydrite (Fh), except for the Pohaku site. The short-range ordered natural Fh (Fh(SRO)) phases were stable at 4°C in the presence of oxygen for at least 1 year and during 400°C treatment. The observed stability of the Fh(SRO) is consistent with magnetic observations that point to non-interacting nanoparticles. PDF analyses of total scattering data provide further evidence for Fh(SRO) particles with a poorly ordered silica coating. The presence of coated particles explains the small CSD for the mat minerals, as well as the stability of the minerals over time and against heating. The mineral properties observed here provide a starting point from which progressively older and more extensively altered Fe deposits may be examined, with the ultimate goal of improved interpretation of past biogeochemical conditions and diagenetic processes.

No MeSH data available.


Related in: MedlinePlus

The Mössbauer spectra show the typical behavior of Loihi FhSRO. At room temperature the spectrum is represented by a doublet and indicates the presence of Fe3+. At 4.2 K the spectrum is a sextet and indicates magnetic order. The sextet has broad lines suggesting the Fe phase is poorly crystallized. The doublet at room temperature represents a phase in a superparamagnetic state.
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Figure 8: The Mössbauer spectra show the typical behavior of Loihi FhSRO. At room temperature the spectrum is represented by a doublet and indicates the presence of Fe3+. At 4.2 K the spectrum is a sextet and indicates magnetic order. The sextet has broad lines suggesting the Fe phase is poorly crystallized. The doublet at room temperature represents a phase in a superparamagnetic state.

Mentions: The room temperature spectra for the Fe mat samples from the Spillway A, Tower, Hiolo A, Ula Nui-A, Ula Nui-B/C, Lohiau A, and BT37 areas of Loihi Seamount have a Fe3+ doublet and magnetic hyperfine parameters corresponding to Fh (Table 5; Figure 8). The presence of a doublet in a Mössbauer spectrum is a feature associated with paramagnetism and/or superparamagnetism. A superparamagnetic phase has magnetic order below the blocking temperature. The Mössbauer spectra of Fe mats taken at 4.2 K have magnetic order and they exhibit a sextet. The magnetic hyperfine parameters of Loihi mat samples at 4.2 K agree with the ones found in the literature for Fh (Berquó et al., 2009). A decrease was observed in the magnetic hyperfine field (BHF) as compared with synthetic Fh; this feature is associated with structural defects. Ferrihydrite, specifically two-line Fh, has significant defects in both the tetrahedral and octahedral Fe(III) sites (Michel et al., 2010), and these natural FhSRO samples from Loihi Seamount seem to have extra Fe(III)-site lattice defects due perhaps to Fe substitution and vacancies.


Mineralogy of iron microbial mats from loihi seamount.

Toner BM, Berquó TS, Michel FM, Sorensen JV, Templeton AS, Edwards KJ - Front Microbiol (2012)

The Mössbauer spectra show the typical behavior of Loihi FhSRO. At room temperature the spectrum is represented by a doublet and indicates the presence of Fe3+. At 4.2 K the spectrum is a sextet and indicates magnetic order. The sextet has broad lines suggesting the Fe phase is poorly crystallized. The doublet at room temperature represents a phase in a superparamagnetic state.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3316996&req=5

Figure 8: The Mössbauer spectra show the typical behavior of Loihi FhSRO. At room temperature the spectrum is represented by a doublet and indicates the presence of Fe3+. At 4.2 K the spectrum is a sextet and indicates magnetic order. The sextet has broad lines suggesting the Fe phase is poorly crystallized. The doublet at room temperature represents a phase in a superparamagnetic state.
Mentions: The room temperature spectra for the Fe mat samples from the Spillway A, Tower, Hiolo A, Ula Nui-A, Ula Nui-B/C, Lohiau A, and BT37 areas of Loihi Seamount have a Fe3+ doublet and magnetic hyperfine parameters corresponding to Fh (Table 5; Figure 8). The presence of a doublet in a Mössbauer spectrum is a feature associated with paramagnetism and/or superparamagnetism. A superparamagnetic phase has magnetic order below the blocking temperature. The Mössbauer spectra of Fe mats taken at 4.2 K have magnetic order and they exhibit a sextet. The magnetic hyperfine parameters of Loihi mat samples at 4.2 K agree with the ones found in the literature for Fh (Berquó et al., 2009). A decrease was observed in the magnetic hyperfine field (BHF) as compared with synthetic Fh; this feature is associated with structural defects. Ferrihydrite, specifically two-line Fh, has significant defects in both the tetrahedral and octahedral Fe(III) sites (Michel et al., 2010), and these natural FhSRO samples from Loihi Seamount seem to have extra Fe(III)-site lattice defects due perhaps to Fe substitution and vacancies.

Bottom Line: Disorder in the nanostructured Fe-bearing phases results in limited intermediate-range structural order: less than that of standard two-line ferrihydrite (Fh), except for the Pohaku site.The presence of coated particles explains the small CSD for the mat minerals, as well as the stability of the minerals over time and against heating.The mineral properties observed here provide a starting point from which progressively older and more extensively altered Fe deposits may be examined, with the ultimate goal of improved interpretation of past biogeochemical conditions and diagenetic processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Soil, Water, and Climate, University of Minnesota-Twin Cities St. Paul, MN, USA.

ABSTRACT
Extensive mats of Fe oxyhydroxides and associated Fe-oxidizing microbial organisms form in diverse geochemical settings - freshwater seeps to deep-sea vents - where ever opposing Fe(II)-oxygen gradients prevail. The mineralogy, reactivity, and structural transformations of Fe oxyhydroxides precipitated from submarine hydrothermal fluids within microbial mats remains elusive in active and fossil systems. In response, a study of Fe microbial mat formation at the Loihi Seamount was conducted to describe the physical and chemical characteristics of Fe-phases using extended X-ray absorption fine structure spectroscopy, powder X-ray diffraction, synchrotron radiation X-ray total scattering, low-temperature magnetic measurements, and Mössbauer spectroscopy. Particle sizes of 3.5-4.6 nm were estimated from magnetism data, and coherent scattering domain (CSD) sizes as small as 1.6 nm are indicated by pair distribution function (PDF) analysis. Disorder in the nanostructured Fe-bearing phases results in limited intermediate-range structural order: less than that of standard two-line ferrihydrite (Fh), except for the Pohaku site. The short-range ordered natural Fh (Fh(SRO)) phases were stable at 4°C in the presence of oxygen for at least 1 year and during 400°C treatment. The observed stability of the Fh(SRO) is consistent with magnetic observations that point to non-interacting nanoparticles. PDF analyses of total scattering data provide further evidence for Fh(SRO) particles with a poorly ordered silica coating. The presence of coated particles explains the small CSD for the mat minerals, as well as the stability of the minerals over time and against heating. The mineral properties observed here provide a starting point from which progressively older and more extensively altered Fe deposits may be examined, with the ultimate goal of improved interpretation of past biogeochemical conditions and diagenetic processes.

No MeSH data available.


Related in: MedlinePlus