TY - JOUR
T1 - Determination and application of the equilibrium oxygen isotope effect between water and sulfite
AU - Wankel, Scott D.
AU - Bradley, Alexander S.
AU - Eldridge, Daniel L.
AU - Johnston, David T.
N1 - Funding Information:
The authors would like to acknowledge the following people for help and or useful advice: Liam Pearson-Conway, Ben Gill and Erin Beirne. This work was supported in part by funding from NASA Astrobiology Institute (DTJ), NSF EAR/IF (DTJ), NSF EAR Low-Temperature Geochemistry and Geobiology (DTJ), Department of Energy Office of Subsurface Biogeochemical Research (DTJ, SDW) and Harvard University.
PY - 2014/1/15
Y1 - 2014/1/15
N2 - The information encoded by the two stable isotope systems in sulfate (δ34SSO4 and δ18OSO4) has been widely applied to aid reconstructions of both modern and ancient environments. Interpretation of δ18OSO4 records has been complicated by rapid oxygen isotope equilibration between sulfoxyanions and water. Specifically, the apparent relationship that develops between δ18OSO4 and δ18 Owater during microbial sulfate reduction is thought to result from rapid oxygen isotope equilibrium between intracellular water and aqueous sulfite - a reactive intermediate of the sulfate reduction network that can back-react to produce sulfate. Here, we describe the oxygen equilibrium isotope effect between water and sulfite (referring to all the sum of all S(IV)-oxyanions including sulfite and both isomers and the dimer of bisulfite). Based on experiments conducted over a range of pH (4.5-9.8) and temperature (2-95°C), where ε=1000*(α-1), we find εSO3-H2O=13.61-0.299*pH-0.081*T°C.Thus, at a pH (7.0) and temperature (25°C) typifying commonly used experimental conditions for sulfate reducing bacterial cultures, sulfite is enriched in 18O by 9.5‰ (±0.8‰) relative to ambient water.We examine the implication of these results in a sulfate reduction network that has been revised to reflect our understanding of the reactions involving oxygen. By evaluating previously published data within this new architecture, our results are consistent with previous suggestions of high reversibility of the sulfate reduction biochemical network. We also demonstrate that intracellular exchange rates between SO32- and water must be on average 1-3 orders of magnitude more rapid than intracellular fluxes of sulfate reduction intermediates and that kinetic isotope effects upstream of SO32- are required to explain previous laboratory and environmental studies of δ18OSO4 resulting as a consequence of sulfate reduction.
AB - The information encoded by the two stable isotope systems in sulfate (δ34SSO4 and δ18OSO4) has been widely applied to aid reconstructions of both modern and ancient environments. Interpretation of δ18OSO4 records has been complicated by rapid oxygen isotope equilibration between sulfoxyanions and water. Specifically, the apparent relationship that develops between δ18OSO4 and δ18 Owater during microbial sulfate reduction is thought to result from rapid oxygen isotope equilibrium between intracellular water and aqueous sulfite - a reactive intermediate of the sulfate reduction network that can back-react to produce sulfate. Here, we describe the oxygen equilibrium isotope effect between water and sulfite (referring to all the sum of all S(IV)-oxyanions including sulfite and both isomers and the dimer of bisulfite). Based on experiments conducted over a range of pH (4.5-9.8) and temperature (2-95°C), where ε=1000*(α-1), we find εSO3-H2O=13.61-0.299*pH-0.081*T°C.Thus, at a pH (7.0) and temperature (25°C) typifying commonly used experimental conditions for sulfate reducing bacterial cultures, sulfite is enriched in 18O by 9.5‰ (±0.8‰) relative to ambient water.We examine the implication of these results in a sulfate reduction network that has been revised to reflect our understanding of the reactions involving oxygen. By evaluating previously published data within this new architecture, our results are consistent with previous suggestions of high reversibility of the sulfate reduction biochemical network. We also demonstrate that intracellular exchange rates between SO32- and water must be on average 1-3 orders of magnitude more rapid than intracellular fluxes of sulfate reduction intermediates and that kinetic isotope effects upstream of SO32- are required to explain previous laboratory and environmental studies of δ18OSO4 resulting as a consequence of sulfate reduction.
UR - http://www.scopus.com/inward/record.url?scp=84891371988&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2013.08.039
DO - 10.1016/j.gca.2013.08.039
M3 - Article
AN - SCOPUS:84891371988
SN - 0016-7037
VL - 125
SP - 694
EP - 711
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -