Present address: Institute of Geography, University of Erlangen-Nürnberg, D-91054 Erlangen, Germany.
Effects of organic matter on carbonate stable isotope ratios (δ13C, δ18O values) – implications for analyses of bulk sediments
Article first published online: 17 FEB 2013
Copyright © 2013 John Wiley & Sons, Ltd.
Rapid Communications in Mass Spectrometry
Volume 27, Issue 6, pages 707–712, 30 March 2013
How to Cite
Oehlerich, M., Baumer, M., Lücke, A. and Mayr, C. (2013), Effects of organic matter on carbonate stable isotope ratios (δ13C, δ18O values) – implications for analyses of bulk sediments. Rapid Commun. Mass Spectrom., 27: 707–712. doi: 10.1002/rcm.6492
- Issue published online: 17 FEB 2013
- Article first published online: 17 FEB 2013
- Manuscript Revised: 14 DEC 2012
- Manuscript Accepted: 14 DEC 2012
- Manuscript Received: 18 OCT 2012
- German Research Foundation. Grant Number: DFG MA 4235/4-1 and MA 4235/4-2, and LU786/7-1
Stable isotope ratio (δ13C, δ18O values) analyses of carbonates can be biased by CO2 release from organic impurities. This is most critical for carbonate isotope analyses from bulk sediments containing comparably high amounts of organic matter (OM). Several methods have been developed to remove OM prior to analyses, but none of them can be universally applied. Moreover, pretreatment methods cause isotopic bias in themselves and should probably best be avoided. Thus, it is essential to have indicators for reliable isotope values of untreated carbonate-OM mixtures.
Artificial mixtures of organic compounds with a standard carbonate were analyzed to investigate the bias on carbonate isotope ratios caused by OM in the sample. The total-inorganic-carbon to total-organic-carbon ratio (TIC/TOC) was used as a measure for the " organic impurity" of the sample. The target was to evaluate TIC/TOC as a measure for sample quality and to define TIC/TOC thresholds for reliable isotope measurements of mixtures between calcium carbonate and organic compounds.
The effect of organic impurities on carbonate stable isotope values depended on the specific OM compound and the respective TIC/TOC ratio. Different CO2 release rates were determined for the pure OM compounds. A sample TIC/TOC ratio ≥0.3 was found to be a threshold for reliable measurements of the isotope composition of calcium carbonate.
Bulk carbonate analyses from carbonate-OM mixtures are reliable only if the TIC/TOC values do not fall below certain thresholds. This has implications for carbonate isotope studies from bulk sediments for which the TIC/TOC ratios should be considered as an easy-to-determine measure for sample-quality assessment. Copyright © 2013 John Wiley & Sons, Ltd.