18 O analyses of bulk lipids as novel paleoclimate tool in loess research – a pilot study

• Published in: E&G Quaternary Science Journal
• Main Authors: J. Labahn, L. Bittner, P. Hirschmann, C.-B. Roettig, D. Burghardt, B. Glaser, S. B. Marković, M. Zech
• Format: Article in Journal/Newspaper
• Language: German; English
• Published: Copernicus Publications 2022
• Subjects: Geology; QE1-996.5; Greenland; Antarc*; Antarctica; Dansgaard-Oeschger events; ice core
• Online Access: https://doi.org/10.5194/egqsj-71-83-2022; https://doaj.org/article/83f7425146b9495d81a8408d9084b9ed

The analysis of the stable oxygen isotopes 18 O and 16 O has revolutionized paleoclimate research since the middle of the last century. Particularly, δ 18 O of ice cores from Greenland and Antarctica is used as a paleotemperature proxy, and δ 18 O of deep-sea sediments is used as a proxy for global ice volume. Important terrestrial archives to which δ 18 O as a paleoclimate proxy is successfully applied are speleothems, lake sediments, or tree rings. By contrast, δ 18 O applications to loess–paleosol sequences (LPSs) are scarce. Here we present a first continuous δ 18 O record ( n =50 ) for the LPS Crvenka in Serbia, southeastern Europe, spanning the last glacial–interglacial cycle (since 145 ka). From a methodological point of view, we took advantage of a recently proposed paleoclimate/paleohydrological proxy based on bulk δ 18 O analyses of plant-derived lipids. The Crvenka δ 18 O bulk lipid values range between −10.2 ‰ and +23.0 ‰ and are systematically more positive in the interglacial and interstadial (paleo-)soils corresponding to marine oxygen-isotope stage (MIS) 1, 3, and 5, compared to the loess layers (MIS 2, 4, and 6). Our Crvenka δ 18 O bulk lipid record provides no evidence for the occurrence of interstadials and stadials comparable to the Dansgaard–Oeschger events known from the Greenland δ 18 O ice core records. Concerning the interpretation of our Crvenka δ 18 O bulk lipid record, plant-derived lipids such as fatty acids and alcohols are certainly strongly influenced by climatic factors such as temperature (via δ 18 O precipitation ) and relative air humidity (via 18 O enrichment of leaf water due to evapotranspiration). However, pool effects in the form of non-water-correlated lipids such as sterols or the input of root-derived lipids need to be considered, too. Similarly, the input of soil-microbial lipids and oxygen exchange reactions represent uncertainties challenging quantitative paleoclimate/paleohydrological reconstructions based on δ 18 O bulk lipid analyses from LPSs.