Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p42c..10c&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P42C-10
Mathematics
Logic
[1041] Geochemistry / Stable Isotope Geochemistry, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The Rio Tinto, a river in southwest Spain, has a long history of acid, iron and sulfate rich water resulting primarily from the oxidation of pyrite (ferrous iron sulfide). Its geochemistry and extremophile microbiology make it an exciting and ideal mars-analogue research site, as relatively recent discoveries have shown Mars to be rich in sulfates believed to have formed in an acidic environment. Current models for the oxidation pathways of pyrite sulfur to sulfate, and the microbial influences on those pathways are incomplete. Traditionally, studies have only focused on d18O as a tracer for the oxygen sources in sulfate and determination of the oxidation pathways. The d18O method has always been fraught with uncertainty due to isotope fractionation during oxygen incorporation from the two dominant sources, atmospheric oxygen and water. A relatively new method utilizing 17O measures the relationship between d17O/d18O. The average relationship has been defined as the Terrestrial Fractionation Line, with a slope of 0.52. Deviations from this relationship are represented as Cap delta 17O, the difference of delta 17O from the expected value. Cap17O values are useful because they depend only on the relationship between d17O/d18O, which remains constant during mass dependent fractionation. During O2 generation from solid BaSO4, some fractionation can occur due to incomplete oxygen yield. This can produce uncertainties in d17O and d18O, but Cap17O is dependent only on the d17O/d18O ratio and is therefore not affected. The relationship mentioned above between d17O/d18O (slope=0.52) is an average for terrestrial materials and it is becoming increasingly clear that process specific slopes can be defined. This offers an exciting opportunity to characterize potential biomarkers on Mars. If a biologically specific slope could be determined, then its signature will be preserved through subsequent mass dependent fractionation processes. Our approach is to use Río Tinto field and laboratory data to define a process specific slope for natural sulfate, produced via oxidation of pyrite. This study presents field data collected in May of 2011 from various inputs on the Rio Tinto system. The pH range was 0.91-3.18, Eh ranged from 556-831mV. Iron and sulfate were the major ionic species and range from 0.105-587mM and 9.6-989mM, respectively. Initial d18O values are between (-1.5 to +6.0) and are reproducible to (0.8). Cap17O values (calculated with a slope=0.528) range between (0.07-0.192) and are reproducible to (0.007). There is a strong linear relationship between d17O and d18O, which defines a slope or maybe process specific slope of 0.5184, with an R squared value of 0.9995. We will present our update on this ongoing work and our conclusion on whether we have developed a new signature of either or both inorganic and biological oxidation to characterize terrestrial and martian sulfates.
Christensen Joseph
Coleman Max L.
Kohl Issaku
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