2008_Biogenic iron oxyhydroxide formation at mid-ocean ridge.pdf

ARTICLE IN PRESSBiogenic iron oxyhydroxide formation at mid-ocean ridge hydrothermal vents: Juan de Fuca Ridge Brandy M. Toner a,*, Cara M. Santelli a, Matthew A. Marcus b, Richard Wirth c, Clara S. Chan a, Thomas McCollom d, Wolfgang Bach a,e, Katrina J. Edwards a,f,g aDepartment of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA bThe Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA cGeoForschungsZentrum Potsdam, Potsdam, Germany dUniversity of Colorado at Boulder, Laboratory for Atmospheric and Space Physics, Boulder, CO, USA eFachbereich Geowissenschaften, Universita?t Bremen, Bremen, Germany fGeomicrobiology Group, Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA gDepartment of Earth Sciences, University of Southern California, Los Angeles, CA, USA Received 22 May 2008; accepted in revised form 19 September 2008Abstract Here we examine Fe speciation within Fe-encrusted biofilms formed during 2-month seafloor incubations of sulfide mineral assemblages at theMain Endeavor Segment of the Juan de FucaRidge. The biofilmswere distributed heterogeneously across the surface of the incubated sulfide and composed primarily of particles with a twisted stalk morphology resembling those produced by some aerobic Fe-oxidizing microorganisms. Our objectives were to determine the form of biofilm-associated Fe, and identify the sulfide minerals associated with microbial growth. We used micro-focused synchrotron-radiation X-ray fluorescence map- ping (lXRF), X-ray absorption spectroscopy (lTXAFS), and X-ray diffraction (lXRD) in conjunction with focused ion beam (FIB) sectioning, andhigh resolution transmission electronmicroscopy (HRTEM).The chemical andmineralogical composition of an Fe-encrusted biofilm was queried at different spatial scales, and the spatial relationship between primary sulfide and sec- ondary oxyhydroxide minerals was resolved. The Fe-encrusted