Unravelling contamination signals in biogenic silica oxygen isotope composition : the role of major and trace element geochemistry

Brewer, T.S.; Leng, Melanie; Mackay, A.W.; Lamb, Angela; Tyler, J.J.; Marsh, N.G.. 2008 Unravelling contamination signals in biogenic silica oxygen isotope composition : the role of major and trace element geochemistry. Journal of Quaternary Science, 23 (4). 321-330. 10.1002/jqs.1171

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The oxygen isotope composition of diatom silica ( 18Odiatom) provides valuable information for palaeoclimate studies where carbonate proxies are either rare or absent in many lakes and ocean sediments. Unfortunately, mineral and rock fragments found alongside diatoms in most sediments can be problematic as the method used will liberate oxygen from all components within the sediment, producing both high-frequency noise and low-frequency excursions that can resemble climate signals. Removal of mineral contamination to date has largely relied upon the combination of chemical leaching and physical separation techniques (e.g. sieving, density). This combination can be inefficient and often significant proportions of contaminants are present in the purified diatom sample. Using electron optical imaging and whole-rock geochemistry on previously purified diatom samples, a mass balance approach has been developed whereby the types and proportions of residual contaminants are identified. By integrating this information with measured oxygen isotope ratios of the contaminants, it is then possible to remove contamination effects from the 18Odiatom record. Contamination effects relating to carbonates, tephra and silt are modelled for cores from Lake Tilo (Ethiopia) and Lake Baikal (Siberia). In both lakes the new modelled 18Odiatom curves show less high-frequency noise, thus enabling better resolution of low-frequency climate signals

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1002/jqs.1171
Programmes: BGS Programmes 2008 > NERC Isotope Geoscience Laboratory
ISSN: 0267-8179
Additional Keywords: Oxygen isotopes, Silica, Trace element geochemistry
NORA Subject Terms: Earth Sciences
Date made live: 04 Jul 2008 14:52 +0 (UTC)

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