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 (FhSRO) 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 FhSRO is consistent with magnetic observations that point to non-interacting nanoparticles. PDF analyses of total scattering data provide further evidence for FhSRO 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.
Keywords: EXAFS, total X-ray scattering, Mössbauer, magnetism, microbial mat, Loihi Seamount, biomineral, nanoparticle
Citation: Toner BM, Berquó TS, Michel FM, Sorensen JV, Templeton AS and Edwards KJ (2012) Mineralogy of iron microbial mats from Loihi Seamount. Front. Microbio. 3:118. doi: 10.3389/fmicb.2012.00118
Received: 22 November 2011; Paper pending published: 27 December 2011;
Accepted: 12 March 2012; Published online: 02 April 2012.
Edited by:David Emerson, Bigelow Laboratory for Ocean Sciences, USA
Reviewed by:John Stolz, Duquesne University, USA
Copyright: © 2012 Toner, Berquó, Michel, Sorensen, Templeton and Edwards. This is an open-access article distributed under the terms of the Creative Commons Attribution Non Commercial License, which permits non-commercial use, distribution, and reproduction in other forums, provided the original authors and source are credited.
*Correspondence: Brandy M. Toner, Department of Soil, Water, and Climate, University of Minnesota-Twin Cities, 1991 Upper Buford Circle, 439 Borlaug Hall, St. Paul, MN, USA. e-mail: email@example.com