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SUMMARY:The oxygen side of sulphate: Sulphur and oxygen isotope effects re
 lated to microbial sulphur cycling - Benjamin Brunner\, Max Planck Institu
 te for Marine Microbiology\, 28359 Bremen\, Germany
DTSTART:20091124T163000Z
DTEND:20091124T173000Z
UID:TALK19546@talks.cam.ac.uk
CONTACT:Alex Piotrowski
DESCRIPTION:The sulphur and oxygen isotope composition of sulphate is a ve
 ry powerful tool. It has been used successfully to identify sulphur source
 s (e.g. sulphates and sulphides)\, to elucidate processes that produce sul
 phate (i.e. oxidation of sulphur compounds) and to quantify their respecti
 ve contribution.\n\nIn contrast to this story of success\, our understandi
 ng of what processes result in the expression of  sulphur and oxygen isoto
 pe fractionation is still very limited. For example\, we know that dissimi
 latory sulphate reduction (DSR) causes sulphur isotope fractionation as we
 ll as oxygen isotope exchange between sulphate and water. In recent years 
 it has become evident that reversibility of the enzymatic steps of DSR dom
 inates the expression of these isotope effects (e.g. Brunner et al.\, 2005
 ). However\, we have only just started to explore what combined sulphur an
 d oxygen isotope effects can be attributed to DSR\, and in what instances 
 we have to assume that other processes\, i.e. oxidative sulphur cycling\, 
 influence net isotope fractionation as well. \n\nOn the scale of global bi
 ogeochemical cycles\, it appears that water is the major source for oxygen
  in sulphate. To date\, it is unresolved why the oxygen isotope compositio
 n of sulphate on a perspective of millions of years (e.g. Turchyn and Schr
 ag\, 2006) does not appear to follow the secular changes in the oxygen iso
 tope composition of water (e.g. Veizer et al.\, 1999).\n\nMy presentation 
 introduces the concept of reversibility of enzymatic steps in microbial pa
 thways. I will address the opportunities that arise when investigating sul
 phur and oxygen isotope effects in sulphur cycling in the light of this fr
 amework. The talk concludes with a discussion of the question: are we miss
 ing an important source for oxygen in sulphate when studying global biogeo
 chemical sulphur cycling?\n\nReferences\n\nBrunner B.\, et al. (2005) A mo
 del for oxygen and sulfur isotope fractionation in sulfate during bacteria
 l sulfate reduction processes.  Geochimica et Cosmochimica Acta\, 69\, 477
 3-4785.\n\nTurchyn A. V.\, Schrag D.P. (2006) Cenozoic evolution of the su
 lfur cycle\; Insight from oxygen isotopes in marine sulfate.  Earth and Pl
 anetary Science Letters\, 241\, 763–779.\n\nVeizer J.\, et al. (1999)  8
 7Sr/86Sr\, d13C and d18O evolution of Phanerozoic seawater.  Chemical Geol
 ogy\, 161\, 59–88.\n\n
LOCATION:Tilley Lecture Theater\, Department of Earth Sciences
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