In situ sulfide removal and CO₂ fixation rates at deep-sea hydrothermal vents and the oxic/anoxic interface in Framvaren Fjord, Norway

We have developed a technique to reproducibly measure sulfide removal rates in situ in aquatic environments, even at remote locations such as deep-sea hydrothermal vents. The technique employs the monobromobimane method for derivatizing thiols in situ which can then later be conveniently analyzed by HPLC. The method can be applied toward a wide variety of geochemical and microbiological studies of sulfur cycling in aquatic habitats. Sulfide removal rates as high as 164 μmol/1/day and 240 μmol/1/day were measured for hydrothermal vents at the Juan de Fuca Ridge and at the oxic/anoxic interface in Framvaren Fjord, Norway, respectively. These are among the highest values reported within the water column of any aquatic habitat. In addition, we simultaneously measured rates of microbial CO₂ fixation in situ at the Galapagos and Juan de Fuca hydrothermal vents and at the oxic/anoxic interface of Framvaren Fjord. Rates of CO₂ fixation at these sites exceeded previous reports and may be the result of shorter incubation times that we employed. The results establish new upper limits for the rates at which these processes occur within these environments and offer interesting comparisons of the extent of microbially mediated sulfide removal and CO₂ fixation between different aquatic habitats.