Micron-scale mapping of sulfur cycling across the oxycline of a cyanobacterial mat

Abstract

We present a parallel microgeochemical and microbiological study of μm-scale sulfur cycling within hypersaline microbial mats from Guerrero Negro, Baja California Sur, Mexico. Diel variations (day/night) in sulfur cycling were investigated in field incubations as well as in mats grown under controlled conditions in the laboratory at NASA Ames Research Center. Sulfur cycling in the laboratory mats was examined under a variety of different sulfate concentrations to evaluate the role this had on sulfide concentration and isotopic composition. Sulfate levels in the overlying water column were: 80 mM SO_4 (natural level at Guerrero Negro); 1 mM SO_4; and 200 uM SO_4. Dissolved sulfide within the mat was captured on silver discs and analyzed for its abundance and δ^(34)S isotopic composition using high resolution secondary ion mass spectrometry (SIMS) on a Cameca 7F Geo.

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