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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

Comparison of PDFs for BT37, Spillway A, and Lohiau A to the Fh reference plotted as G(r)*r2 versus r to amplify the features at higher r values. Although subtle for the natural samples the features >∼4 Å are reasonable similar to those of synthetic Fh. Note that the PDF for Fh was also multiplied by 0.25 for comparison. Ula Nui-A and -B also showed similar features but due to impurities (e.g., birnessite) were excluded for clarity.
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FA3: Comparison of PDFs for BT37, Spillway A, and Lohiau A to the Fh reference plotted as G(r)*r2 versus r to amplify the features at higher r values. Although subtle for the natural samples the features >∼4 Å are reasonable similar to those of synthetic Fh. Note that the PDF for Fh was also multiplied by 0.25 for comparison. Ula Nui-A and -B also showed similar features but due to impurities (e.g., birnessite) were excluded for clarity.

Mentions: With exception of the degree of PDF decay, the most significant differences between the Loihi mat FhSRO and Fh reference are in the range 2.5 < r < 4 Å. As described above, differences in this region of the PDFs appear primarily due to Si…Fe pair correlations. Interestingly, the pair correlations beyond r ≈ 4 Å in BT37, Ula Nui-A, Spillway A, and Lohiau A closely resemble synthetic Fh (Figure A3 in Appendix) suggesting that the intermediate-range order and connectivity of Fe polyhedra are maintained over these length scales. The PDF peaks decay at r ≈ 16 Å for BT37, Spillway A, and Lohiau A suggesting that these mat samples are more disordered and have smaller CSD sizes compared with synthetic two-line Fh which decays at r ≈ 23 Å (Figure A3 in Appendix). Estimated CSD sizes for Ula Nui-A and Ula Nui-B (Table 3) are significantly larger (∼23 and 37 Å, respectively) however, the presence of relatively crystalline impurities in these samples prevents an accurate estimate for the Fh fractions, which are assumed to be less crystalline than the associated impurity phases. Shifts in peak positions for the natural samples relative to Fh at higher r (>4 Å) may be attributable, in part, to increasing strain with decreasing CSD size, and this trend is consistent with previous studies of synthetic Fh in which the size and/or Fe(III) vacancy content varied (Michel et al., 2007a).


Mineralogy of iron microbial mats from loihi seamount.

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

Comparison of PDFs for BT37, Spillway A, and Lohiau A to the Fh reference plotted as G(r)*r2 versus r to amplify the features at higher r values. Although subtle for the natural samples the features >∼4 Å are reasonable similar to those of synthetic Fh. Note that the PDF for Fh was also multiplied by 0.25 for comparison. Ula Nui-A and -B also showed similar features but due to impurities (e.g., birnessite) were excluded for clarity.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

FA3: Comparison of PDFs for BT37, Spillway A, and Lohiau A to the Fh reference plotted as G(r)*r2 versus r to amplify the features at higher r values. Although subtle for the natural samples the features >∼4 Å are reasonable similar to those of synthetic Fh. Note that the PDF for Fh was also multiplied by 0.25 for comparison. Ula Nui-A and -B also showed similar features but due to impurities (e.g., birnessite) were excluded for clarity.
Mentions: With exception of the degree of PDF decay, the most significant differences between the Loihi mat FhSRO and Fh reference are in the range 2.5 < r < 4 Å. As described above, differences in this region of the PDFs appear primarily due to Si…Fe pair correlations. Interestingly, the pair correlations beyond r ≈ 4 Å in BT37, Ula Nui-A, Spillway A, and Lohiau A closely resemble synthetic Fh (Figure A3 in Appendix) suggesting that the intermediate-range order and connectivity of Fe polyhedra are maintained over these length scales. The PDF peaks decay at r ≈ 16 Å for BT37, Spillway A, and Lohiau A suggesting that these mat samples are more disordered and have smaller CSD sizes compared with synthetic two-line Fh which decays at r ≈ 23 Å (Figure A3 in Appendix). Estimated CSD sizes for Ula Nui-A and Ula Nui-B (Table 3) are significantly larger (∼23 and 37 Å, respectively) however, the presence of relatively crystalline impurities in these samples prevents an accurate estimate for the Fh fractions, which are assumed to be less crystalline than the associated impurity phases. Shifts in peak positions for the natural samples relative to Fh at higher r (>4 Å) may be attributable, in part, to increasing strain with decreasing CSD size, and this trend is consistent with previous studies of synthetic Fh in which the size and/or Fe(III) vacancy content varied (Michel et al., 2007a).

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