Journal of Paleolimnology

, Volume 44, Issue 4, pp 947–961

Molecular fingerprinting of wetland organic matter using pyrolysis-GC/MS: an example from the southern Cape coastline of South Africa

  • Andrew S. Carr
  • Arnoud Boom
  • Brian M. Chase
  • David L. Roberts
  • Zoë E. Roberts
Original paper
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Abstract

Pyrolysis–gas chromatography mass spectrometry (py-GC/MS) allows the characterisation of complex macromolecular organic matter. In lakes and wetlands this can potentially be used to assess the preservation/diagenesis and provenance of sediment organic matter. It can complement palaeoenvironmental investigations utilising ‘bulk’ sediment variables such as total organic carbon (TOC) and TOC/total nitrogen ratios. We applied py-GC/MS analyses to a ~32,000-year sediment record from the southern Cape coastline of South Africa. We used the results to evaluate the sources and extent of degradation of organic matter in this semi-arid environment. Marked down-core changes in the relative abundance of multiple pyrolysis products were observed. Correspondence analysis revealed that the major driver of this down-core variability in OM composition was selective preservation/degradation. Samples comprising highly degraded OM are primarily confined to the lower half of the core, older than ~12,000 years, and are characterised by suites of low-molecular-weight aromatic pyrolysis products. Samples rich in organic matter, e.g. surface sediments, are characterised by products derived from fresh emergent or terrestrial vegetation, which include lignin monomers, plant-derived fatty acids and long-chain n-alkanes. Pyrolysates from the late glacial-early Holocene period, approximately mid-way down the core are characterised by distinct suites of long-chain n-alkene/n-alkane doublets, which may reflect the selective preservation of recalcitrant aliphatic macromolecules and/or enhanced inputs of the algal macromolecule algaenan/polymerised algal lipids. Increased TOC, lower δ13C and increased abundance of more labile lignin and fatty acid products at the same depths suggest this period was associated with increased lake primary productivity and enhanced inputs of terrestrial OM. TOC is the only ‘bulk’ parameter correlated with the correspondence analysis axes extracted from the py-GC/MS data. Distinct fluctuations in TOC/total nitrogen ratio are not explained by variation in organo-nitrogen pyrolysis products. Notwithstanding, the study suggests that py-GC/MS has potential to complement palaeolimnological investigations, particularly in regions such as southern Africa, where other paleoenvironmental proxy variables in sediments may be lacking or equivocal.

Keywords

Py-GC/MS Biomarker Quaternary, Diagenesis Lignin 

Supplementary material

10933_2010_9466_MOESM1_ESM.pdf (497 kb)
Supplementary material 1 (PDF 497 kb)

Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Andrew S. Carr
    • 1
  • Arnoud Boom
    • 1
  • Brian M. Chase
    • 2
  • David L. Roberts
    • 3
  • Zoë E. Roberts
    • 1
  1. 1.Department of GeographyUniversity of LeicesterLeicesterUK
  2. 2.Department of Archaeology, History, Cultural Studies and ReligionUniversity of BergenBergenNorway
  3. 3.Council for GeoscienceCape TownSouth Africa

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