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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 11 | Copyright
Clim. Past, 14, 1607-1624, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Nov 2018

Research article | 02 Nov 2018

Leaf wax n-alkane distributions record ecological changes during the Younger Dryas at Trzechowskie paleolake (northern Poland) without temporal delay

Bernhard Aichner1, Florian Ott2,3, Michał Słowiński4, Agnieszka M. Noryśkiewicz5, Achim Brauer2, and Dirk Sachse6 Bernhard Aichner et al.
  • 1Institute of Earth and Environmental Sciences, University of Potsdam, 14476 Potsdam-Golm, Germany
  • 2Section 5.2: Climate Dynamics and Landscape Evolution, GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany
  • 3Department of Archaeology, Max Planck Institute for the Science of Human History, 07745 Jena, Germany
  • 4Department of Environmental Resources and Geohazards, Institute of Geography and Spatial Organisation, Polish Academy of Sciences, 00-818 Warsaw, Poland
  • 5Institute of Archaeology, Faculty of History, Nicolaus Copernicus University, 87-100 Toruń, Poland
  • 6Organic Surface Geochemistry Lab, Section 5.1: Geomorphology, GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany

Abstract. While of higher plant origin, a specific source assignment of sedimentary leaf wax n-alkanes remains difficult. In addition, it is unknown how fast a changing catchment vegetation would be reflected in sedimentary leaf wax archives. In particular, for a quantitative interpretation of n-alkane C and H isotope ratios in terms of paleohydrological and paleoecological changes, a better understanding of transfer times and dominant sedimentary sources of leaf wax n-alkanes is required.

In this study we tested to what extent compositional changes in leaf wax n-alkanes can be linked to known vegetation changes by comparison with high-resolution palynological data from the same archive. We analyzed leaf wax n-alkane concentrations and distributions in decadal resolution from a sedimentary record from Trzechowskie paleolake (TRZ, northern Poland), covering the Late Glacial to early Holocene (13360–9940yrBP). As an additional source indicator of targeted n-alkanes, compound-specific carbon isotopic data have been generated in lower time resolution. The results indicated rapid responses of n-alkane distribution patterns coinciding with major climatic and paleoecological transitions. We found a shift towards higher average chain length (ACL) values at the Allerød–Younger Dryas (YD) transition between 12680 and 12600yrBP, coevaled with a decreasing contribution of arboreal pollen (mainly Pinus and Betula) and a subsequently higher abundance of pollen derived from herbaceous plants (Poaceae, Cyperaceae, Artemisia), shrubs, and dwarf shrubs (Juniperus and Salix). The termination of the YD was characterized by a successive increase in n-alkane concentrations coinciding with a sharp decrease in ACL values between 11580 and 11490yrBP, reflecting the expansion of woodland vegetation at the YD–Holocene transition. A gradual reversal to longer chain lengths after 11200yrBP, together with decreasing n-alkane concentrations, most likely reflects the early Holocene vegetation succession with a decline of Betula.

These results show that n-alkane distributions reflect vegetation changes and that a fast (i.e., subdecadal) signal transfer occurred. However, our data also indicate that a standard interpretation of directional changes in biomarker ratios remains difficult. Instead, responses such as changes in ACL need to be discussed in the context of other proxy data. In addition, we find that organic geochemical data integrate different ecological information compared to pollen, since some gymnosperm genera, such as Pinus, produce only a very low amount of n-alkanes and for this reason their contribution may be largely absent from biomarker records. Our results demonstrate that a combination of palynological and n-alkane data can be used to infer the major sedimentary leaf wax sources and constrain leaf wax transport times from the plant source to the sedimentary sink and thus pave the way towards quantitative interpretation of compound-specific hydrogen isotope ratios for paleohydrological reconstructions.

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Short summary
Abundances of plant biomarkers are compared with pollen data in a 3000-year climate archive covering the Late Glacial to Holocene transition in northern Poland. Both parameters synchronously show the rapid onset (12680–12600 yr BP) and termination (11580–11490 yr BP) of the Younger Dryas cold interval in the study area. This demonstrates the suitability of such proxies to record pronounced changes in vegetation cover without significant delay.
Abundances of plant biomarkers are compared with pollen data in a 3000-year climate archive...