Bacterially-Produced Iron Oxide Minerals at Juan de Fuca Ridge As part of my NASA Astrobiology Institute postdoctoral research
(joint between Katrina Edwards at the Woods Hole Oceanographic
Institution and Mitchell Sogin at Marine Biological
Laboratory), I have developed a structural model for the biogenic
minerals formed by iron (Fe) oxidizing bacteria by taking a polyhedral
approach to fitting Fe
K-edge EXAFS data (Combes et al., 1989; Manceau et al., 1993; Toner et al., in prep). At
the Juan de Fuca Ridge, the activity of Fe oxidizing bacteria has been
assessed through seafloor sulfide mineral incubation studies (Edwards
et al., 2003). These mineral incubations provided a
time-constrained view of microbial colonization of sulfide minerals, as
well as the production of secondary minerals by Fe oxidizing
bacteria. Edwards and co-workers reported that after two months
at the seafloor, the sulfide mineral surfaces were colonized at
densities of 7 – 50 × 104 cells per mm2.
In addition, colonization density was correlated with the solubility
and porosity of the sulfide minerals. On the most heavily
colonized mineral, a natural chimney sulfide from Juan de Fuca Ridge,
large accumulations of Fe- and O-rich particles with distinctly
microbiological morphologies formed over and within pore spaces.
While select particles were found to diffract electrons, and give a
pattern corresponding to the structurally poorly-defined Fe oxide
mineral 2-line ferrihydrite, the Fe associated with the twisted stalk
microbiological particles did not diffract electrons. In
collaboration with Cara Santelli (then MIT-WHOI Joint Program Ph.D. student, now Harvard postdoc), Katrina Edwards (now USC), Wolfgang Bach (University of Bremen), and Matthew Marcus (Advanced Light Source),
I have conducted a study of these poorly-crystalline biogenic minerals
using a series of spatially-resolved approaches: micro-focused EXAFS,
micro-focused XRD, and TEM-FIB. The results of this study are in
preparation for publication. Picture: Katrina Edwards, Brandy Toner, and Cara Santelli at the Advanced Light Source BL10.3.2 in March 2007. References and More Information: Toner, B. M., Santelli, C. M., Marcus, M. A., Bach, W., and Edwards, K. J. (in prep) Biogenic Iron Oxide Formation at Mid-Ocean Ridge Hydrothermal Vents: Juan de Fuca Ridge. Toner, B.M., Santelli, C.M., Bach, W., Toner, B.M., Santelli, C.M., Rogers, D.M., and Edwards, K.J. Low-Temperature Weathering of Hydrothermal Sulfide Minerals at Juan de Fuca Ridge. Crustal Construction, Tectonic, Alteration, Microbiological, and Transport Processes on the Flanks of Mid-Ocean Ridges. Eos Trans.AGU, 86(52), Fall Meet. Suppl. Abstract T33A-0518, 2005. Poster. Edwards K. J., McCollom T. M., Konishi H., and Buseck P. R. (2003) Seafloor bioalteration of sulfide minerals: Results from in situ incubation studies. Geochim. Cosmochim. Acta 67(15), 2843-2856. Combes J. M., Manceau A., Calais G., and Bottero J. Y. (1989) Formation of ferric oxides from aqueous solutions: A polyhedral approach by X-ray absorption spectroscopy: I. Hydrolysis and formation of ferric gels. Geochim. Cosmochim. Acta 53, 583-594. Manceau A. and Drits V. A. (1993) Local Structure of Ferrihydrite and Feroxyhite by EXAFS Spectroscopy. Clay Minerals 28, 165-184. Acronymns: EXAFS - extended X-ray absorption fine structure (spectroscopy) XRD - X-ray diffraction TEM-FIB - transmission electron microscopy (with focused ion beam sectioning) |
| Low-temperature Weathering of Extinct Hydrothermal Chimneys at East Pacific Rise We studied seafloor weathering of
hydrothermal chimney sulfide minerals at the East Pacific Rise (EPR) 9N
from the perspective of secondary iron (Fe) mineral
formation. The hydrothermal chimney sulfides examined in this
study represent an approximate time-series in the life cycle of
hydrothermal chimneys, from active chimneys to long-extinct
sulfide rubble. We used micrometer-focused
synchrotron-radiation X-ray fluorescence (XRF) to create 2D maps of the
elemental distribution of Se, As, Zn, Cu, Ni, Fe, Mn, Cr, V, Ti, Ca, K,
Cl, S, and Si at the micron scale. With the XRF maps as a guide,
we examined the mineral structure (Fe K-edge EXAFS and XRD) and Fe
isotopic signature (laser ablation MC-ICP-MS) of Fe-rich and S-depleted
products of weathering, as well as the primary sulfide minerals.
The secondary Fe oxide minerals in our samples were: (1) present
as coatings or replacement of sulfide minerals, and (2) in close
association with with K- and Si-rich materials. Our Fe EXAFS
results reveal the presence of a continuum of Fe oxide
minerals. The end members in this continuum of Fe oxide
structures are simple Fe-O octahedral chains and goethite,
respectively. The mass spectrometry results indicate
that two Fe oxide formation mechanisms are possible. We interpret
the Fe-isotope signatures of goethite and ferrihydrite as reflecting
primarily different Fe oxidizing environments related to: (1) direct
oxidation from Fe from pyrite in massive sulfide under oxygenated
seawater conditions, and (2) Fe oxidation from late stage
Fe-Si-rich hydrothermal fluids in chimney environments. Seafloor
hydrothermal systems at mid-ocean ridges encompass fundamental
processes controlling the exchange of heat and chemical species between
seawater and ocean crust, and support diverse and unique biological
communities capable of using dissolved chemical species and minerals
for energy metabolism. The new laser ablation MC-ICP-MS analytical capability coupled to
spatially-resolved elemental and mineralogical data (synchrotron
radiation XRF, XRD, and XAS) is expected to provide further constraints
on: (1) the complex interactions between hydrothermal fluids, seawater,
and sulfide minerals over a wide range of temperature and redox
conditions, and (2) potential biosignatures of Fe-oxidizing and
Fe-S-reducing bacteria in chimney environments.
For this research, the synchrotron-radation XRF, XRD, and XAS was conducted in collaboration with Matthew Marcus (ALS), Cara Santelli (Harvard), and Katrina Edwards (USC), and the laser ablation MC-ICP-MS research was conducted in collaboration with Olivier Rouxel (WHOI). References: Toner, B., Santelli, C.M., Marlow, J.J., Rouxel, O., and Edwards, K.J. Microbe-Mineral Interactions in Extinct Hydrothermal Chimneys at East Pacific Rise: Spatially-Resolved Chemical and Mineralogical Approaches. Biofilms in the Environment: Adaptive Roles, Microbe-Mineral Interactions, and Contributions to Global Biogeochemical Cycles. Eos Trans. AGU, 87(52), Fall Meet. Suppl., Abstract B14B-02, 2006. Invited talk. Toner, B. M., Santelli, C. M., Rouxel, O., and Edwards, K. J. (in prep) Sea-floor weathering of extinct hydrothermal chimney sulfide minerals from East Pacific Rise 9N: coupled, fine spatial-scale X-ray fluorsecence, X-ray absorption spectroscopy, and laser-ablation MC-ICP-MS analyses. |
| Iron and Carbon in Hydrothermal Plume Particulates at East Pacific Rise *Under Construction* References:
Toner, B.M, Fakra, S.C, Manganini, S.J., Moffett, J.W., German, C.R., and Edwards, K.J. Particulate Organic Carbon and Iron Speciation within Deep-Sea Hydrothermal Plumes. Geomicrobiology and Environmental Biogeochemistry of Iron and Manganese. Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract B23G-08. Talk. Brandy M. Toner, Sirine C. Fakra, Steven J. Manganini, Cara M. Santelli, Matthew A. Marcus, James W. Moffett, Olivier Rouxel, Christopher R. German, and Katrina J. Edwards (in prep) Iron(II) is Stable in Association with Particulate Organic Carbon in Deep-sea Hydrothermal Plumes. |