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Biotic and abiotic degradation of alkenones and implications for U₃₇[superscript K′] paleoproxy applications. A review Pubblico Deposited

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  • Lipid biomarkers in sediments are widely used to infer environmental conditions that have occurred in the geological past, but these reconstructions require a careful consideration of the biotic and abiotic processes that degrade and alter the lipid biomarker compositions before and after deposition. In this paper, we use alkenones produced by haptophyte microalgae to explore the range of effects of these degradative processes. Alkenones are now perhaps the best studied of all biomarkers with several hundred papers on their occurrence in organisms, seawater and sediments. Much information has been obtained on their degradation from laboratory incubations and inferences from changes in their distribution in aquatic environments. Although alkenones are often considered as more stable than many other lipid classes, it is now clear that their distributions can be affected by processes such as prolonged oxygen exposure, aerobic bacterial degradation and thiyl radical-induced stereomutation processes which, in some cases, can lead to changes in the proportions of the alkenones used in the U₃₇[superscript K′] temperature proxy. The same set of chemical and biological processes act on all lipids in aquatic environments and, in cases where there is a marked difference in reactivity, this may lead to significant changes in the biomarker distributions and relative proportions of different lipid classes.
  • Keywords: Stereomutation, Alkenones, Photooxidation, Autoxidation, Biotic and abiotic degradation, Aerobic and anaerobic biodegradation, Lipid tracers, Sulfurization, Paleotemperature estimations
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  • Rontani, J.-F., Volkman, J. K., Prahl, F. G., & Wakeham, S. G. (2013). Biotic and abiotic degradation of alkenones and implications for U-37(K') paleoproxy applications: A review. Organic Geochemistry, 59, 95-113. doi:10.1016/j.orggeochem.2013.04.005
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  • 59
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  • JFR gratefully acknowledges financial support over many years from the CNRS-INSU and the Université de la Méditerranée. FP acknowledges long standing support from the US NSF-OCE for his study of alkenone biogeochemistry in the marine environment. SGW has also been supported by the US NSF-OCE and gratefully acknowledges the Hanse Wissenschaftskolleg (Hanse Institute for Advanced Studies), Delmenhorst, Germany, for a fellowship that supported the preparation of this review. Thanks are also due to the Oregon State University Core Repository for providing SE Alaskan surface sediment samples for analysis (NSF grant number: 0962077-OCE).
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