Microbial and hydrothermal aspects of ferric oxyhydroxides and ferrosic hydroxides: the example of Franklin Seamount, Western Woodlark Basin, Papua New Guinea

Abstract

Deposits of Fe-Si-Mn oxyhydroxides are commonly found on the seafloor on seamounts and mid-ocean spreading centers. At Franklin Seamount located near the western extremity of Woodlark Basin, Papua New Guinea, Fe-Si-Mn oxyhydroxides are being precipitated as chimneys and mounds upon a substrate of mafic lava. Previous studies have shown that the vent fluids have a low temperature (20-30 uC) and are characterized by a total dissolved iron concentration of 0.038 mM kg 21 , neutral pH (6.26) and no measurable H 2 S. The chimneys have a yellowish appearance with mottled red-orange patches when observed in situ from a submersible, but collected samples become redder within a few hours of being removed from the sea. The amorphous iron oxyhydroxides, obtained from active and inactive vents, commonly possess filamentous textures similar in appearance to sheaths and stalks excreted by the iron-oxidizing bacteria Leptothrix and Gallionella; however, formless agglomerates are also common. Textural relationships between apparent bacterial and non-bacterial iron suggest that the filaments are coeval with and/or growing outwards from the agglomerates. The amorphous iron oxyhydroxides are suggested to precipitate hydrothermally as ferrosic hydroxide, a mixed-valence (Fe 2z -Fe 3z ) green-yellow iron hydroxide compound. Consideration of the thermodynamics and kinetics of iron in the vent fluid, suggest that the precipitation is largely pH controlled and that large amounts of amorphous iron oxyhydroxides are capable of being precipitated by a combination of abiotic hydrothermal processes. Some biologically induced precipitation of primary ferric oxyhydroxides (two-XRD-line ferrihydrite) may have occurred directly from the fluid, but most of the filamentous iron microtextures in the samples appear to have a diagenetic origin. They may have formed as a result of the interaction between the iron-oxidizing bacteria and the initially precipitated ferrosic hydroxide that provided a source of ferrous iron needed for their growth. The processes described at Franklin Seamount provide insight into the formation of other seafloor oxyhydroxide deposits and ancient oxide-facies iron formation.

Molecular Comparison of Bacterial Communities within Iron-Containing Flocculent Mats Associated with Submarine Volcanoes along the Kermadec Arc

“…These filaments are found as thin layers on seafloor rocks (16) and lava crusts (29), on sulfides and devices incubated at venting sites (10,23), and as thick flocculent mats covering vast areas near hydrothermal environments (1,20,22,34). The sheaths and filaments are often visually similar to those produced by the neutrophilic Fe-oxidizing betaproteobacteria Leptothrix spp.…”

“…Samples of flocculent mat material with Fe-oxide filaments have been obtained from Loihi Seamount, Hawaii; Franklin Seamount, Papua New Guinea; Juan de Fuca Ridge, northeast Pacific Ocean; Vailulu'u Seamount, Samoa; and recently from cold seeps located at the Chefren Mud Volcano (Nile Deep Sea Fan, eastern Mediterranean) (1,20,22,27,34). This study adds evidence for the occurrence of these biogenic Fe-oxides at locations with hydrothermal venting.…”

Four-Hundred-and-Ninety-Million-Year Record of Bacteriogenic Iron Oxide Precipitation at Sea-Floor Hydrothermal Vents

“…The filaments are usually between 1 and 5 µmindiameter, and 10s to 100s µm long. Many have distinctive morphologies, including twisted ribbons, hollow sheaths and dendritic filaments (Alt 1988;Juniper and Fouquet 1988;Stoffers et al 1993;Halbach et al 2001;Thorseth et al 2001;Boyd and Scott 2001;Emerson and Moyer 2002;Kennedy et al 2003aKennedy et al , 2003bKennedy et al , 2003c. Several authors have noted the similarity of these morphologies with structures formed by neutrophilic Fe-oxidizing bacteria, including Gallionella ferruginea, which grows Fe encrusted twisted stalks (e.g., Hanert 1973Hanert , 2002, and Leptothrix ochracea, which forms Fe oxide encrusted sheaths (e.g., Emerson and Revsbech 1994).…”

“…The mineralogy of these Fe oxide deposits is dominated by poorly ordered Fe oxyhydroxides (Two-XRDline ferrihydrite and goethite), often with significant amounts of amorphous silica (up to 73 wt%) and Mn (up to 14 wt%) (Alt 1988;Juniper and Fouquet 1988;Binns et al 1993;Hekinian et al 1993;Stoffers et al 1993;Fortin, Ferris, and Scott 1998;Iizasa et al 1998;Boyd and Scott 2001;Emerson and Moyer 2002;Kennedy, Scott, and Ferris 2003a).…”

Chemical and Isotopic Compositions of Hydrothermal Fluids at Snail, Archaean, Pika, and Urashima Sites in the Southern Mariana Trough

“…On the seafloor, sinking organic matter is very sparse, but flourishing ecosystems are sustained around hydrothermal fields despite high temperatures and pressures (Deming and Baross 1993;Takai and Horikoshi 1999;Kelley et al 2002). Ecosystems utilizing Fe for energy have been extensively documented, especially around low-temperature hydrothermal vents (e.g., Boyd and Scott 2001;Edwards 2004;Edwards et al 2003, 2011; Little et al 2004;Kato et al 2009;Langley et al 2009;Toner et al 2009). Ecosystems based on metabolism of inorganic materials are of interest for their potential insight into the origins of life (e.g., Alt 1988;Juniper and Fouquet 1988;Duhig et al 1992;Juniper and Tebo 1995;Hofmann and Farmer 2000;Reysenbach and Cady 2001).…”