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TitleLow-temperature formation and stabilization of rare allotropes of cyclooctasulfur (beta-S8 and gamma-S8) in the presence of organic carbon at a sulfur-rich glacial site in the Canadian High Arctic
AuthorLau, G; Cosmidis, J; Grasby, S; Trivedi, C; Spear, J; Templeton, A
SourceGeochimica et Cosmochimica Acta vol. 200, 2016 p. 218-231,
Alt SeriesEarth Sciences Sector, Contribution Series 20160213
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories; Nunavut
NTS340; 540; 39; 49; 59; 69
Lat/Long WENS-104.0000 -72.0000 84.0000 76.0000
Subjectsgeochemistry; regional geology; sulphur; organic carbon; glaciers; mineralization; x-ray diffraction; x-ray diffraction analyses; infrared spectral analyses; sulphides; allotropes; cyclo ocatsulphur
Illustrationslocation maps; photographs; schematic diagrams; tables; graphs; photomicrographs
ProgramWestern Arctic, High Arctic LIP, GEM2: Geo-mapping for Energy and Minerals
AbstractLarge-scale deposits of elemental sulfur form annually on a glacier's surface at Borup Fiord Pass in the Canadian High Arctic. However, the mechanisms of mineralization and stabilization of elemental sulfur at this site are currently unknown. Here we show that x-ray diffraction (XRD) data for fresh sulfur precipitates collected from the surface of a melt pool over sulfide-rich ice reveal the presence of three sulfur allotropes, a-S8, ß-S8, and gamma-S8 (the three solid forms of cyclooctasulfur (S8)). The detection of the ß-S8 allotrope of elemental sulfur is notable, since ß-S8 typically only forms in high temperature environments (>96°C). The gamma-S8 allotrope is also rare in natural settings and has previously been implicated as a signature of microbial sulfur cycling. Using combustion and infrared spectroscopy approaches, organic carbon is also detected within the sample bearing the three allotropes of elemental sulfur. Electron microscopy and scanning transmission x-ray microscopy (STXM) at the C K-edge show that the sulfur precipitates are intimately associated with the organic carbon at the submicron scale. The occurrence of ß-S8 and gamma-S8 in this low-temperature setting indicates that there are unknown pathways for the formation and stabilization of these rare allotropes of elemental sulfur. In particular, we infer that the occurrence of these allotropes is related to their association with organic carbon. The formation of carbon-associated sulfur globules may not be a direct by-product of microbial activity; however, a potential role of direct or indirect microbial mediation in the formation and stabilization of ß-S8 and gamma-S8 remains to be assessed.
Summary(Plain Language Summary, not published)
Unusual sulphur minerals (called 'beta sulphur and gamma sulphur') were found in the high arctic during GEM field work. These are sulphur compounds forming on the surface of a glacier. The minerals previously have only been thought to form in very high temperature environments. This discovery challenges these previous models for controls on the formation of these minerals. Results are important as they indicate that these minerals can no longer be used as an indicator of a high temperature environment of formation. They may also have relevance as an important biomarker, a sign of life, that is key in interplanetary exploration.