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Archaeol as a methanogen biomarker in ombrotrophic bogs |
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| Authors: | Richard D Pancost Erin L McClymont Elizabeth M BinghamZoë Roberts Dan J CharmanEdward RC Hornibrook Anthony BlundellFrank M Chambers Katie LH LimRichard P Evershed |
| Institution: | a Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre and The Cabot Institute, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK b School of Geography, College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4RJ, UK c Bristol Biogeochemistry Research Centre and The Cabot Institute, School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, UK d Department of Geography, University of Leeds, Leeds LS2 9JT, UK e Centre for Environmental Change and Quaternary Research, Department of Natural & Social Sciences, University of Gloucestershire, Francis Close Hall, Swindon Rd., Cheltenham GL50 4AZ, UK |
| Abstract: | In order to develop new tools in the reconstruction of microbiological processes in ancient continental settings, we determined the concentration of archaeol and sn-2-hydroxyarchaeol in four Holocene ombrotrophic peatlands, spanning a range of European climate zones. Neither ether lipid was present in the aerobic acrotelm peat, consistent with an origin from anaerobic archaea, presumably methanogens. At the depth of the maximum seasonal water table, archaeol and sn-2-hydroxyarchaeol concentration markedly increased at all four sites, again consistent with an anaerobic source, but differed strongly among sites. The differences apparently reflect a combination of vegetation - ericaceous and graminoid plants as opposed to Sphagnum spp. and other mosses lacking root systems - and temperature influence on methanogenesis. In particular, low ether lipid concentrations in Finland probably reflect the lack of vascular vegetation possessing well-developed root systems, together with low mean annual temperature. Similarly low concentrations of archaeol and sn-2-hydroxyarchaeol in a German bog likely result from winter temperatures below 0 °C and a relatively shorter growing season. The occurrence of sn-2-hydroxyarchaeol is limited to a narrow and shallow depth range, indicating that it is poorly preserved, but archaeol persists throughout the cores. Decoupling the concentration of archaeol and the more labile sn-2-hydroxyarchaeol below ca. 50 cm suggests that the former records fossil biomass rather than living biomass. If so, then downcore variation in archaeol concentration likely reflects past changes in methane cycling, and archaeol, pending further developmental research, could serve as a new tool for reconstruction of past peatland biogeochemistry. |
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