Sulfate reduction energetics at Main Endeavor grotto chimney from samples collected on RV Atlantis (AT18-08) during Jason II dives in the Juan de Fuca Ridge from July to August 2011 (NCEI Accession 0277879)

Acquisition Description:
Tables and Figures referenced in the acquisition description are found in the paper Frank et al., 2015

For each independent treatment, aliquots of 7.5 mL flange slurry (approx. 29 g wet weight and 20 g dry weight) were transferred into Balch tubes in an anaerobic chamber, and supplemented with 15 mL of sterile artificial seawater media designed to mimic the geochemical conditions within a hydrothermal flange (400 mM NaCl, 25 mM KCl, 30 mM CaCl2, 2.3 mM NaHCO3, 14 mM NaSO42-, 1 mM H2S, and 50 uM dissolved organic carbon - consisting of equimolar proportions 10 uM of pyruvate, citrate, formate, acetate, lactate) under a pure nitrogen headspace.

Concentrations of sulfide, sulfate and dissolved organic carbon (DOC) were varied independently to investigate concentration dependent effects on the rates of SR. The range of experimental conditions tested was determined from previously published concentration profiles of aqueous species modeled as functions of temperature and position within the Grotto vent structure (Tivey, 2004). Concentrations were varied by orders of magnitude within the modeled ranges to simulate conditions representative of different mixing regimes between seawater and vent fluid (Table 1). The range of DOC (which we approximate as a mix of pyruvate, citrate, formate, acetate, lactate – most of which have been identified to varying degrees within vent fluid and are known carbon sources for heterotrophic SR in culture) concentrations tested were based on the average DOC concentrations measured within diffuse fluids at the Main Endeavor Field (Lang et al., 2006; Lang et al., 2010). Hydrogen sulfide was present as H2S (pKa in seawater of 6.60) across all the conditions tested (Amend & Shock, 2001). Incubations were carried out at pH 4 (to simulate the pH of end-member Grotto vent fluid and the average calculated pH of mixed fluids in highly reduced zones within the flange; Tivey 2004) as well as pH 6 (representative of the calculated pH in fluid mixing zones; Tivey 2004). All the results are presented and discussed in the context of the initial measured media conditions.