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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 19 | Copyright
Biogeosciences, 15, 5831-5845, 2018
https://doi.org/10.5194/bg-15-5831-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 04 Oct 2018

Research article | 04 Oct 2018

Quantification of lignin oxidation products as vegetation biomarkers in speleothems and cave drip water

Inken Heidke1, Denis Scholz2, and Thorsten Hoffmann1 Inken Heidke et al.
  • 1Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg University of Mainz, Duesbergweg 10–14, 55128 Mainz, Germany
  • 2Institute of Geosciences, Johannes Gutenberg University of Mainz, J.-J.-Becher-Weg 21, 55128 Mainz, Germany

Abstract. Here we present a sensitive method to analyze lignin oxidation products (LOPs) in speleothems and cave drip water to provide a new tool for paleo-vegetation reconstruction. Speleothems are valuable climate archives. However, compared to other terrestrial climate archives, such as lake sediments, speleothems contain very little organic matter. Therefore, very few studies on organic biomarkers in speleothems are available. Our new sensitive method allows us to use LOPs as vegetation biomarkers in speleothems.

Our method consists of acid digestion of the speleothem sample followed by solid-phase extraction (SPE) of the organic matter. The extracted polymeric lignin is degraded in a microwave-assisted alkaline CuO oxidation step to yield monomeric LOPs. The LOPs are extracted via SPE and finally analyzed via ultrahigh-performance liquid chromatography (UHPLC) coupled to electrospray ionization (ESI) and high-resolution Orbitrap mass spectrometry (HRMS). The method was applied to stalagmite samples with a sample size of 3–5g and cave drip water samples with a sample size of 100–200mL from the Herbstlabyrinth-Advent Cave in Germany. In addition, fresh plant samples, soil water, and powdered lignin samples were analyzed for comparison. The concentration of the sum of eight LOPs (Σ8) was in the range of 20–84ng g−1 for the stalagmite samples and 230–440ng L−1 for the cave drip water samples. The limits of quantification for the individual LOPs ranged from 0.3–8.2ng per sample or 1.5–41.0ng mL−1 of the final sample solution.

Our method represents a new and powerful analytical tool for paleo-vegetation studies and has great potential to identify the pathways of lignin incorporation into speleothems.

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We developed a sensitive method to analyze the lignin composition of organic traces contained in speleothems. Lignin is a main constituent of woody plants and its composition contains information about the type of vegetation. This method offers new possibilities to reconstruct the vegetation of past millennia since it combines the advantages of lignin analysis as a highly specific vegetation biomarker with the benefits of speleothems as unique terrestrial climate archives.
We developed a sensitive method to analyze the lignin composition of organic traces contained in...
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