Multiple sulfur isotopes fractionations associated with abiotic sulfur transformations in Yellowstone National Park geothermal springs

Abstract

BackgroundThe paper presents a quantification of main (hydrogen sulfide and sulfate), as well as of intermediate sulfur species (zero-valent sulfur (ZVS), thiosulfate, sulfite, thiocyanate) in the Yellowstone National Park (YNP) hydrothermal springs and pools. We combined these measurements with the measurements of quadruple sulfur isotope composition of sulfate, hydrogen sulfide and zero-valent sulfur. The main goal of this research is to understand multiple sulfur isotope fractionation in the system, which is dominated by complex, mostly abiotic, sulfur cycling.ResultsWater samples from six springs and pools in the Yellowstone National Park were characterized by pH, chloride to sulfate ratios, sulfide and intermediate sulfur species concentrations. Concentrations of sulfate in pools indicate either oxidation of sulfide by mixing of deep parent water with shallow oxic water, or surface oxidation of sulfide with atmospheric oxygen. Thiosulfate concentrations are low (<6 μmol L-1) in the pools with low pH due to fast disproportionation of thiosulfate. In the pools with higher pH, the concentration of thiosulfate varies, depending on different geochemical pathways of thiosulfate formation. The δ34S values of sulfate in four systems were close to those calculated using a mixing line of the model based on dilution and boiling of a deep hot parent water body. In two pools δ34S values of sulfate varied significantly from the values calculated from this model. Sulfur isotope fractionation between ZVS and hydrogen sulfide was close to zero at pH < 4. At higher pH zero-valent sulfur is slightly heavier than hydrogen sulfide due to equilibration in the rhombic sulfur–polysulfide – hydrogen sulfide system. Triple sulfur isotope (32S, 33S, 34S) fractionation patterns in waters of hydrothermal pools are more consistent with redox processes involving intermediate sulfur species than with bacterial sulfate reduction. Small but resolved differences in ∆33S among species and between pools are observed.ConclusionsThe variation of sulfate isotopic composition, the origin of differences in isotopic composition of sulfide and zero–valent sulfur, as well as differences in ∆33S of sulfide and sulfate are likely due to a complex network of abiotic redox reactions, including disproportionation pathways.

Impact of Aeolian Dry Deposition of Reactive Iron Minerals on Sulfur Cycling in Sediments of the Gulf of Aqaba

“…As sulfate and water do not exchange oxygen isotopes easily, this observed oxygen isotope exchange is attributed to the intracellular exchange of oxygen atoms between sulfur intermediate species (such as sulfite) and water (Mizutani and Rafter, 1973; Fritz et al, 1989). The observed 18 O isotope enrichment over the isotopic composition of water (magnitude 22 - 30‰) reflects intracellular oxygen isotope exchange (Böttcher et al, 1998, 1999; Brunner et al, 2005, 2012; Turchyn et al, 2006, 2010; Antler et al, 2013). Therefore, if a significant fraction of sulfate is reduced and reoxidized to sulfate, exchange of oxygen isotopes between sulfate and water can be detected, and thus the oxygen isotopic composition of sulfate may be a proxy for any quantitative cycling of sulfur such as during a cryptic sulfur cycle (Bishop et al, 2013; Johnston et al, 2014).…”

Geologic legacy spanning >90 years explains unique Yellowstone hot spring geochemistry and biodiversity

“…2B to 2K). Previous XRD analyses conducted on sediments sampled in 2013 (pH 5.5, 78.6°C) confirm the presence of S° in EP (Colman et al ., ) and HPLC analyses conducted on waters collected in 2014 (pH 6.5, 81.0°C) reveal concentrations of dissolved S° as high as 3 mM dispersed in the water column (Kamyshny Jr. et al ., ). Moreover, EP waters contain up to 320 μM polysulfide (S x 2− ) (Lorenson, ), which are soluble linear chains of S°, and elevated concentrations of sulphite (SO 3 2− ; 3 μM) and S 2 O 3 2− (560 μM) have been detected in this spring (Kamyshny Jr. et al ., ).…”

“…Previous XRD analyses conducted on sediments sampled in 2013 (pH 5.5, 78.6°C) confirm the presence of S° in EP (Colman et al ., ) and HPLC analyses conducted on waters collected in 2014 (pH 6.5, 81.0°C) reveal concentrations of dissolved S° as high as 3 mM dispersed in the water column (Kamyshny Jr. et al ., ). Moreover, EP waters contain up to 320 μM polysulfide (S x 2− ) (Lorenson, ), which are soluble linear chains of S°, and elevated concentrations of sulphite (SO 3 2− ; 3 μM) and S 2 O 3 2− (560 μM) have been detected in this spring (Kamyshny Jr. et al ., ). A comparison to other sulphur rich, acidic springs in YNP (e.g., Cinder Pool, ‘Dragon Spring’ and Frying Pan Spring) indicates that the high amounts of suspended S°, soluble S x 2− and S 2 O 3 2− in EP is a unique feature in YNP (Kamyshny Jr. et al ., ), particularly given its moderate acidity.…”

“…2H‐2K). Based on SO 4 2− and Cl − numbers during this time interval, it was estimated that somewhere between 85% and 100% of the water in EP was from the parent HO water body (Kamyshny Jr. et al ., ).…”

“…The increase to moderately acidic pH also promoted shifts in the microbial activities taking place in the spring that may have included SO 4 2− reduction (SR), an activity that is generally favoured in more moderate (pH 5 to 9) conditions (Postgate, ). SR activity would decrease SO 4 2− concentrations by converting it to sulphide that, in turn, either volatilized from the spring or reacted with remnant S° to form soluble S x 2− , which have been measured at high concentrations in EP (Kamyshny Jr. et al ., ). Importantly, dissolved O 2 concentrations in EP in 2013 and 2016 were 25.3 and 12.6 μM (Colman et al ., ; Dahlquist, ).…”