Login

Join for Free!
118246 members
table of contents table of contents

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

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

mcith_07090903f01.jpg Figure 1 Location map of Franklin Seamount, Western Woodlark Basin, Papua New Guinea. [6,7].

(Click image to enlarge)

mcith_07090903f02.jpg Figure 2 Photographs of Fe–Si–Mn oxyhydroxides at Franklin Sea-mount. (a) In situ fresh staghorn chimney spire taken from submersible. Note the mottled pale color of the oxyhydroxides becomes more reddish towards the base (see arrow), (b) hand sample of oxyhydroxide taken on ship deck exhibiting red ferric iron with a sooty black manganiferous exterior. Photographs 2a and b courtesy of Raymond Binns, CSIRO, Australia. Thin section photographs of Fe–Si–Mn oxyhydroxides from Franklin Seamount. (c) and (d) iron mineralization attached to hair-like structures, sample M2192 loc. 1 (106848), note the faint outline of the filaments in association with the structures (see arrows), height of images 70 μm. (e) Filaments exhibiting a branching morphology (see arrows), sample M2157-14a (106893), height of image 70 μm. (f) Filaments exhibiting a bunched morphology, M2157-14a (106893), height of image 170 μm.

(Click image to enlarge)

mcith_07090903f03.jpg Figure 3 SEM images of Fe–Si–Mn oxyhydroxides from Franklin Sea-mount. (a) Typical filamentous texture, sample M2170-8 (106905). (b) Apparently branching filaments thickened by silica carapaces (see arrow), sample M2202-6 (106925), photograph courtesy of Katsumi Marumo, Geological Survey of Japan, Japan, (c) Bunched filament made of parallel strands surrounded by amorphous iron agglomerates (see arrow), sample M2202-2a-1 (106920). (d) Short braided stalk in center (see arrow) surrounded by amorphous iron oxyhydroxides, M2202-2a-1 (106920). (e) Formless agglomerates of amorphous iron oxyhydroxide, sample M2202-2a-1 (106920). (f) and (g) Filaments (see arrows) attached or growing outwards from agglomerates of amorphous iron oxyhydroxide, M2192 loc. 1 (106848). Spot energy dispersive spectroscopy analyses show no significant compositional difference between the filamentous and formless textures, (h) Degraded filaments, M2170-2B (106899). Note the lack of degradation in those filaments adjacent to the formless textures in (c), (d), (f) and (g); these textures are very different from (h).

(Click image to enlarge)

mcith_07090903f04.jpg Figure 4 TEM images of microbial forms in Fe–Si–Mn oxyhydroxides from Franklin Seamount. (a) and (b) Typical fragments of anhedral agglomerates of amorphous iron oxyhydroxides, sample M2202–2A-1 (106920), height of images 2.6 μm. (c) Pseudo? branching filament, sample M2022-3B (106926), height of image 13 μm. (d) Filament exhibiting hollow structure, sample M2192 loc. 1 (106848), height of image 2.6 μm. The walls consist of regular bands of amorphous iron-silica oxyhydroxides. (e) Braided filament, sample M2202-2a-1 (106920), height of images 4 μm. (f) Amorphous iron oxyhydroxides (see arrow) agglomerated on a typical filament, sample M2202-2a-1 (106920), height of images 5 μm.

(Click image to enlarge)

mcith_07090903f05.jpg Figure 5 f(O2) vs. pH iron stability diagram at 25°C and 1 bar showing the natural domains of the main groups of iron oxidizing bacteria recalculated from an Eh–pH diagram in Lundgren and Dean.[21] Activities of dissolved iron, carbonate, and sulfur species are 10-6, 10° and 10-6, respectively, from Garrels and Christ.[75] The boundary between Fe3+ and Fe2+ which is missing in the Lundgren and Dean diagram, has been added here. Other thermodynamic databases suggest the presence of FeHCO+3 supplanting siderite between 6.4 and 7.0 pH and acetates supplant other phases and species below -75 logf(O2).

(Click image to enlarge)

mcith_07090903f06.jpg Figure 6 Change in stability boundaries in Fe–O–H system with age of the amorphous iron oxyhydroxides at 25°C, 240 bar and [Fetotal] = 3.9 × 10-5 m calculated and based on the physical and geochemical conditions of the Franklin Seamount vent fluid reported in ref. 5. (1) Freshly precipitated Fe(OH)3, ref. 36. (2) 4-day old Fe(OH)3, ref. 39 and 40. (3) Aged Fe(OH)3, ref. 39. (4) Age of Fe(OH)3 unknown, ref. 25. Thermodynamic data for Fe3(OH)8 is for freshly precipitated material.[39] Calculated with aid from SUPCRT92 program.[19]

(Click image to enlarge)

mcith_07090903f07.jpg Figure 7 Phase equilibria of freshly precipitated oxyhydroxides in the Fe–Si–O–H system (1) from Fig. 6 at 25°C, 240 bar, [Fetotal] = 3.9 × 10-5 m and [Si] = 3.4 × 10-4 m which are the physical and geochemical conditions of a vent fluid at Franklin Seamount and at higher temperatures. Calculated and based on the reactions in Table 3 which are drawn from the thermodynamic databases of Sadiq and Lindsay[39] for Fe2+ and Fe3(OH)8, Langmuir36 for Fe(OH)3, and Winters and Buckley[43] for FeSiO3. The stability fields (*) of iron bacteria from Fig. 5 are at 25°C. Dashed lines show change in Fe2+-Fe3(OH)8-Fe(OH)3 boundaries with increase in temperature. Faint line based on the SUPCRT92 database19 for the dissociation of water plotted to show the sensitivity of the Fe(OH)3-Fe3(OH)8 boundary to minute changes in Gibbs free energies. Calculated with aid of SUPCRT92 program. The arrow represents the upward extrapolation to the Fe2+-solid phases boundaries of the measured pH (6.26) of the 20–30°C vent fluid at Franklin Seamount.

(Click image to enlarge)

mcith_07090903f08.jpg Figure 8 Various possible biotic and hydrothermal processes at an iron oxyhydroxide chimney on the seafloor.

(Click image to enlarge)

mcith_07090903f09.jpg Figure 9 Calculated pH of the intersection point for Fe2+, Fe3(OH)8 and Fe(OH)3 mineral equilibria for compositions of various low temperature vent fluids vs. the actual measured pH of the vent fluid at the site based upon data presented in the literature. 1 Franklin Seamount (ref. 5), 2 Galapagos Rift (ref. 61), 3 Loihi Seamount (ref. 60), 4 Axial Seamount (ref. 47), 5 Kasuga Seamounts (ref. 61), 6 21N East Pacific Rise (ref. 62), 7 Guaymas Basin (ref. 62).

(Click image to enlarge)

mcith_07090903f10.jpg Figure 10 Phase equilibria of ancient iron-formation at 25°C in the Fe–Si–O–H system using composition of Franklin Seamount vent fluid ([Fetotal] = 3.9 × 10-5m and [Si] = 3.4 × 10-4m). (1) Boundaries based on free energy data from Klein and Bricker.[64] Fe3(OH)8 has converted to Fe3O4 while Fe(OH)3 persists unstably (see text). (2) Boundaries based on Fe3O4 in equilibrium with Fe2O3. Closed square represents location of Franklin Seamount vent fluid from Fig. 7.

(Click image to enlarge)

 


rating: 3.38 from 8 votes | updated on: 9 Jul 2009 | views: 17867 |

Rate article:







excellent!bad…