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Using Multi-Homologue Plant-Wax Carbon Isotope Signatures to Reconstruct Tropical Vegetation Types
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  • Christoph Häggi,
  • Dailson J Bertassoli Jr,
  • Thomas K Akabane,
  • Rachel T So,
  • André Oliveira Sawakuchi,
  • Cristiano Mazur Chiessi,
  • Vinicius Ribau Mendes,
  • Carlos Jaramillo,
  • Sarah J Feakins
Christoph Häggi
University of Southern California

Corresponding Author:[email protected]

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Dailson J Bertassoli Jr
University of São Paulo
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Thomas K Akabane
University of São Paulo
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Rachel T So
University of Southern California
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André Oliveira Sawakuchi
University of São Paulo
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Cristiano Mazur Chiessi
University of São Paulo
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Vinicius Ribau Mendes
Institute of Marine Science, Federal University of São Paulo
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Carlos Jaramillo
Smithsonian Tropical Research Institute
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Sarah J Feakins
University of Southern California
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Abstract

The stable carbon isotope composition (δ13C) of plant components such as plant wax biomarkers is an important tool for reconstructing past vegetation. Plant wax δ13C is mainly controlled by photosynthetic pathways, allowing for the differentiation of C4 tropical grasses and C3 forests. Proxy interpretations are however complicated by additional factors such as aridity, vegetation density, elevation, and the considerable δ13C variability found among C3 plant species. Moreover, studies on plant wax δ13C in tropical soils and plants have focused on Africa, while structurally different South American savannas, shrublands and forests remain understudied. Here, we analyze the δ13C composition of long-chain n-alkanes and fatty acids from tropical South American soils and leaf litter to assess the isotopic variability in each vegetation type and to investigate the influence of climatic features on δ13C. Rainforests and open vegetation types show distinct values, with rainforests having a narrow range of low δ13C values (n-C29 n-alkane: -34.5 +0.9/-0.6 ‰ ; Suess-effect corrected) allowing for the detection of even minor incursions of savanna into rainforests (13C-enriched). While Cerrado savannas and semi-arid Caatinga shrublands grow under distinctly different climates, they can yield indistinct δ13C values for most compounds. Cerrado soils and litter show pronounced isotopic spreads between the n-C33 and n-C29 alkanes, while Caatinga shrublands show consistent values across the two homologues, thereby enabling the differentiation of these vegetation types. The same multi-homologue isotope analysis can be extended to differentiate African shrublands from savannas.
12 Dec 2023Submitted to ESS Open Archive
21 Dec 2023Published in ESS Open Archive