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Towards organic carbon isotope records from stalagmites: coupled d13C and 14 C analysis using wet chemical oxidation

Lechleitner, Franziska A. and Lang, Susan Q. and Haghipour, Negar and McIntyre, Cameron and Baldini, James U.L. and Prufer, Keith M. and Eglinton, Timothy I. (2019) 'Towards organic carbon isotope records from stalagmites: coupled d13C and 14 C analysis using wet chemical oxidation.', Radiocarbon., 61 (3). pp. 749-764.

Abstract

Speleothem organic matter can be a powerful tracer for past environmental conditions and karst processes. Carbon isotope measurements (δ13C and 14C) in particular can provide crucial information on the provenance and age of speleothem organic matter, but are challenging due to low concentrations of organic matter in stalagmites. Here, we present a method development study on extraction and isotopic characterization of speleothem organic matter using a rapid procedure with low laboratory contamination risk. An extensive blank assessment allowed us to quantify possible sources of contamination through the entire method. Although blank contamination is consistently low (1.7 ± 0.34 – 4.3 ± 0.86 μg C for the entire procedure), incomplete sample decarbonation poses a still unresolved problem of the method, but can be detected when considering both δ13C and 14C values. We test the method on five stalagmites, showing reproducible results on samples as small as 7 μg C for δ13C and 20 μg C for 14C. Furthermore, we find consistently lower non-purgeable organic carbon (NPOC) 14C values compared to the carbonate 14C over the bomb spike interval in two stalagmites from Yok Balum Cave, Belize, suggesting overprint of a pre-aged or even fossil source of carbon on the organic fraction incorporated by these stalagmites.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:https://www.cambridge.org/core/journals/radiocarbon/article/towards-organic-carbon-isotope-records-from-stalagmites-coupled-13c-and-14c-analysis-using-wet-chemical-oxidation/7326D57C0DF9D89C352D8DB3F152ABCF
Publisher statement:This article has been published in a revised form in Radiocarbon [https://doi.org/10.1017/RDC.2019.35]. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works. © 2019 by the Arizona Board of Regents on behalf of the University of Arizona
Date accepted:No date available
Date deposited:23 April 2019
Date of first online publication:23 April 2019
Date first made open access:23 October 2019

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