HR: 10:35h
AN: B52A-02    [Abstracts]
TI: Micron-scale resolution of sulfur cycling in a microbial mat
AU: * Fike, D A
EM: dfike@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., MC 100-23, Pasadena, CA 91125, United States
AU: Gammon, C
EM: gammon@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., MC 100-23, Pasadena, CA 91125, United States
AU: Ziebis, W
EM: wziebis@usc.edu
AF: University of Southern California, 3616 trousdale Pkwy, AHF 335, Los Angeles, CA 90089, United States
AU: Treude, T
EM: treude@usc.edu
AF: University of Southern California, 3616 trousdale Pkwy, AHF 335, Los Angeles, CA 90089, United States
AU: Eiler, J
EM: eiler@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., MC 100-23, Pasadena, CA 91125, United States
AU: Guan, Y
EM: yunbin@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., MC 100-23, Pasadena, CA 91125, United States
AU: Orphan, V
EM: vorphan@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., MC 100-23, Pasadena, CA 91125, United States
AB: Microbial mats, finely laminated layers of metabolically diverse microbial communities, likely dominated biogeochemical cycling throughout most of Earth history. To further our understanding of biogeochemical processes within microbial mats, we have investigated sulfur cycling (as recorded by sulfate reduction) in mats from Guerrero Negro, Baja California Sur. We have pursued a combined microbiological (CARD-FISH) and microgeochemical (nanoSIMS) approach to understanding sulfur cycling in the hopes to establish the link between microbial metabolic activity and the establishment of geochemical gradients at the micron-scale. CARD-FISH analysis indicates that viable sulfate reducers form coherent bands (on the order of 100um in thickness) throughout at least the upper ~5mm of microbial mat. There appears to be no degradation in banding with depth below the uppermost few millimeters. We present a high-resolution spatial profile of sulfide abundance and isotopic (d34S) composition on the micron-scale using a Cameca NanoSIMS 50L ion microprobe. We find fine-scale (0.1-1mm) banding of sulfide throughout the mats. In addition, there are micron- scale (~4um) laminations observed using the NanoSIMS both in optical CCD and element scanning mode. 2D maps of sulfide abundance and d34S profile from the mat surface down to a depth of ~1cm were obtained at ~50um resolution with a typical analytical error in d34S of ±1 permil (1sigma). Horizontal banding (parallel to mat laminations) of d34S is observed at the scale of 50 – 200 um. These profiles trend toward depleted d34S with depth by up to 25 permil within the upper 1 cm of the mat. Control experiments in standard solutions did not reveal any banding or the same scale of isotopic variability as observed in the microbial mat. We therefore believe that the banding and isotopic variability observed in the microbial mat are not an analytical artefact, but rather reflect very-fine-scale lamination in microbial activity preserved at depth within the mat, as is supported by CARD-FISH observations. As such, the laminations at depth within these mats are not merely relict architecture but reflect ongoing metabolic activity that is subject to the same sharp spatial gradients as are found in the upper few mm of the mat surface. The environmental conditions that maintain such rigid laminations at depth (~1 cm), far from the sharp redox gradients of the mat surface, remain poorly constrained. Thus, our results suggest that the full scope of sulfur cycling with microbial mats is far from completely understood.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0448 Geomicrobiology
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0488 Sulfur cycling
SC: Biogeosciences [B]
MN: 2007 Fall Meeting