Novel methodological approaches in loess research – interrogating biomarkers and compound-specific stable isotopes

Abstract

Abstract. Löss-Paläoboden Sequenzen sind wichtige terrestrische Archive für die Rekonstruktion der quartären Landschafts- und Klimageschichte. Die Entwicklung neuer, quantitativerer Paläoklima-Proxies könnte in den kommenden Jahren eine neue Ära in der Lössforschung einleiten. Dieser Review-Artikel stellt die Prinzipien, die zugrunde liegende Analytik, und erste Anwendungsbeispiele für einige dieser Proxies vor, welche derzeit entwickelt werden. Wir diskutieren das Potential von (i) pflanzenwachsbürtigen n-Alkanen als Biomarker für die Rekonstruktion der Vegetationsgeschichte, (ii) Aminosäure Razemisierung und Glycerin-Dialkyl-Glycerin-Tetraether (GDGT) Indizes als Proxies für die Rekonstruktion der Paläotemperatur und (iii) substanzspezifischen δD and δ18O Analysen an pflanzenbürtigen n-Alkanen bzw. Zuckern für die Entwicklung von Proxies zur Rekonstruktion von Paläoklima/-aridität. Während wir versuchen, die Leserschaft für die methodischen und analytischen Neuentwicklungen und deren Potential für die Lössforschung zu begeistern, verweisen wir gleichzeitig auch auf die Limitierungen und Schwächen der jeweiligen Methoden. So müssen beispielsweise Degradationseffekte oder postsedimentäre ‚Kontamination’ bei der Interpretation von Biomarker-Rekords berücksichtigt und weiter untersucht werden. Des Weiteren könnte sich die Quantifizierung der unterschiedlichen Einflussfaktoren auf Deuterium- und 18O-Rekords als herausfordernd erweisen.

How dry was the Younger Dryas? Evidence from a coupled <i>δ</i><sup>2</sup>H–<i>δ</i><sup>18</sup>O biomarker paleohygrometer applied to the Gemündener Maar sediments, Western Eifel, Germany

“…When considering that both δ 13 C TOC and TOC/N values of terrestrial organic matter are additionally affected by mineralisation and degradation, resulting in more positive δ 13 C TOC values and lower TOC/N ratios (e.g. Zech et al, 2007), a straightforward interpretation of those proxies seems to be challenging. Similarly, δ 15 N has been investigated as proxy for sedimentary organic matter origin (Meyers and Ishiwatari, 1993;Meyers and Lallier-Vergés, 1999;Wolfe et al, 1999).…”

“…With regard to the sugar biomarkers, they were previously studied in detail by Hepp et al (2016). According to the authors' own results and a compilation from the literature (including, e.g., Jia et al, 2008;Prietzel et al, 2013;Zech et al, 2012Zech et al, , 2014b, relatively high amounts of arabinose are a good indicator of a primarily terrestrial origin (higher vascular plants) of the sugars. This interpretation is in agreement with the Gemündener Maar being a small lake with densely forested steep crater walls (Fig.…”

“…Mügler et al, 2008;Zech et al, 2015). Apart from δ 2 H n-alkane , the oxygen isotope composition of hemicellulose-or polysaccharide-derived sugars (δ 18 O sugar ) was established as a tool in paleoclimate research during recent years (Zech et al, 2011(Zech et al, , 2013a(Zech et al, , 2014a. Analogous to δ 2 H n-alkane , δ 18 O sugar is affected by the isotope composition of source water, which is closely related to the local precipi-tation (δ 18 O prec ) as well as by evapotranspirative 18 O enrichment (Tuthorn et al, 2014;Zech et al, 2013bZech et al, , 2014b.…”

Chemotaxonomic patterns of vegetation and soils along altitudinal transects of the Bale Mountains, Ethiopia, and implications for paleovegetation reconstructions – Part II: lignin-derived phenols and leaf-wax-derived <i>n</i>-alkanes

“…n-alkanes are important constituents of plant leaf waxes (Kolattukudy, 1970), where they serve to protect plants against water loss by evaporation as well as from fungal and insect attacks (Eglinton and Hamilton, 1967;Koch et al, 2009). Due to their recalcitrant nature, they are often well preserved in sedimentary archives and used as biomarkers (also called molecular fossils) in paleoclimate and environmental studies (Eglinton and Eglinton, 2008;Glaser and Zech, 2005;Zech et al, 2011c). The potential of n-alkanes for chemotaxonomic studies has been suggested based on the finding that the homologues C 27 and C 29 are sourced pre-dominantly from trees and shrubs, whereas the homologues C 31 and C 33 are sourced predominantly from grasses and herbs (Maffei, 1996;Maffei et al, 2004;Rommerskirchen et al, 2006;Schäfer et al, 2016;Zech, 2009).…”

“…Potential pitfalls when applying n-alkane proxies in paleovegetation studies should not be overlooked. For instance, (Bush and McInerney, 2013) caution against the chemotaxonomic application of n-alkanes because of high n-alkane pattern variability within graminoids and woody plants (Schäfer et al, 2016) emphasized the need for establishing regional calibration studies and Zech et al, (2011aZech et al, ( , 2013 point to degradation affecting n-alkane proxies.…”