BGD Biogeosciences Discussions BGD Biogeosciences Discuss. 1810-6285 Göttingen, Germany 10.5194/bgd-9-9875-2012 Technical Note: <i>n</i>-Alkane lipid biomarkers in loess: post-sedimentary or syn-sedimentary? Zech M. 1 2 3 Kreutzer S. 2 4 Goslar T. 5 Meszner S. 6 Krause T. 1 2 6 Faust D. 6 Fuchs M. 4 Department of Soil Physics, University of Bayreuth, Universitätsstr. 30, 95440 Bayreuth, Germany Geographical Institute, Geomorphology, University of Bayreuth, Universitätsstr. 30, 95440 Bayreuth, Germany Terrestrial Biogeosciences, Martin-Luther-Universität Halle-Wittenberg, Von-Seckendorff-Platz 3, 06120 Halle (Saale), Germany Department of Geography, Justus-Liebig-University Giessen, Senckenbergstr. 1, 35390 Giessen, Germany Poznan Radiocarbon Laboratory, ul. Rubiez 46, 61-612 Poznan, Poland Department of Geography, Chair of Physical Geography, Dresden University of Technology, Helmholtzstr. 10, 01069 Dresden, Germany 31 07 2012 9 7 9875 9896 Copyright: © 2012 M. Zech et al. 2012 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/preprints/9/9875/2012/bgd-9-9875-2012.html The full text article is available as a PDF file from https://bg.copernicus.org/preprints/9/9875/2012/bgd-9-9875-2012.pdf

There is an ongoing discussion whether <i>n</i>-alkane biomarkers – and organic matter (OM) from loess in general – reflect a syn-sedimentary paleoenvironmental and paleoclimate signal or whether they are significantly a post-sedimentary feature contaminated by root-derived OM. We present first radiocarbon data for the <i>n</i>-alkane fraction of lipid extracts and for the first time luminescence ages for the Middle to Late Weichselian loess-paleosol sequence of Gleina in Saxony, Germany. Comparison of these biomarker ages with sedimentation ages as assessed by optically stimulated luminescence (OSL) dating shows that one <i>n</i>-alkane sample features a syn-sedimentary age (<sup>14</sup>C: 29.2 ± 1.4 kyr cal BP versus OSL: 27.3 ± 3.0 kyr). By contrast, the <sup>14</sup>C ages derived from the other <i>n</i>-alkane samples are clearly younger (20.3 ± 0.7 kyr cal BP, 22.1 ± 0.7 kyr cal BP and 29.8 ± 1.4 kyr cal BP) than the corresponding OSL ages (26.6 ± 3.1 kyr, 32.0 ± 3.5 kyr and 45.6 ± 5.3 kyr). This finding suggests that a post-sedimentary <i>n</i>-alkane contamination presumably by roots has occurred. <br><br> In order to estimate the post-sedimentary <i>n</i>-alkane contamination more quantitatively, we applied a <sup>14</sup>C mass balance calculation based on the measured pMC (percent modern carbon) values, the calculated syn-sedimentary pMC values and pMC values suspected to reflect likely time points of post-sedimentary contamination (current, modern, 3 kyr, 6 kyr and 9 kyr). Accordingly, current and modern root-contamination would account for up to 7%, a 3 kyr old root-contamination for up to 10%, and an Early and Middle Holocene root-contamination for up to 20% of the total sedimentary <i>n</i>-alkane pool. <br><br> We acknowledge and encourage that these first radiocarbon results need further confirmation both from other loess-paleosol sequences and for different biomarkers, e.g. carboxylic acids or alcohols as further lipid biomarkers.

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