Sulfide Oxidation across Diffuse Flow Zones of Hydrothermal Vents

Abstract

The sulfide (H 2 S/HS -) that is emitted from hydrothermal vents begins to oxidize abiotically with oxygen upon contact with ambient bottom water, but the reaction kinetics are slow. Here, using in situ voltammetry, we report detection of the intermediate sulfur oxidation products polysulfides [S 2Àx ] and thiosulfate [S 2 O 2À 3 ], along with contextual data on sulfide, oxygen, and temperature. At Lau Basin in 2006, thiosulfate was identified in less than one percent of approximately 10,500 scans and no polysulfides were detected. show either thiosulfate or polysulfides. These in situ data indicate that abiotic sulfide oxidation does not readily occur as H 2 S contacts oxic bottom waters. Calculated abiotic potential sulfide oxidation rates are \10 -3 lM/min and are consistent with slow oxidation and the observed lack of sulfur oxidation intermediates. It is known that the thermodynamics for the first electron transfer step for sulfide and oxygen during sulfide oxidation in these systems are unfavorable, and that the kinetics for two electron transfers are not rapid. Here, we suggest that different metal catalyzed and/or biotic reaction pathways can readily produce sulfur oxidation intermediates. Via shipboard high-pressure incubation experiments, we show that snails with chemosynthetic endosymbionts do release polysulfides and may be responsible for our field observations of polysulfides.

Evidence for the role of endosymbionts in regional-scale habitat partitioning by hydrothermal vent symbioses

“…In situ voltammetry and a temperature probe were used to determine free sulfide and oxygen concentrations as well as fluid temperatures associated with a subset of the Alviniconcha collections (Table S1) (83,84). Measurements were made in the same manner for both diffuse flows and chimney walls.…”

Chemistry, Temperature, and Faunal Distributions at Diffuse-Flow Hydrothermal Vents: Comparison of Two Geologically Distinct Ridge Systems

“…Thiosulfate has only been detected at the ELSC Waite et al, 2008;Gartman et al, 2011) and in less than 4% of the scans. Thiosulfate is formed near brownish sediments containing iron(III) (oxy)hydroxides and manganese(III,IV) oxides and (oxy) hydroxides, which are known to oxidize H 2 S rapidly (Pyzik and Sommer, 1981;Yao and Millero, 1996;Herszage and Afonso, 2003).…”

“…2009 (Gartman et al, 2011), and at 9 N EPR from 2004Lutz et al, 2008;Nees et al, 2008Nees et al, , 2009Crespo-Medina et al, 2009;Moore et al, 2009), including the change in chemistry after the 2005-2006 eruptions described by Tolstoy et al (2006). In these studies, an in situ electrochemical analyzer (Ferrini et al, 2008;Ryan et al, 2009) electrode was used in conjunction with the deep-submergence vehicle (DSV)…”

“…Polysulfides have rarely been detected at both the ELSC and 9 N EPR (Luther et al, 2001Gartman et al, 2011).…”

“…Thiosulfate is formed near brownish sediments containing iron(III) (oxy)hydroxides and manganese(III,IV) oxides and (oxy) hydroxides, which are known to oxidize H 2 S rapidly (Pyzik and Sommer, 1981;Yao and Millero, 1996;Herszage and Afonso, 2003). Gartman et al (2011) and H 2 S/T ratios decreased from north to south at the ELSC sites, which may be due to a combination of the geological substrate and the larger geological mass or volume (due to shallower water column depths in the south) for H 2 S in the source fluids to penetrate and react with solid substrate and reduce source H 2 S concentrations before reaching the bottom waters.…”