C01_02

A dual chronological approach for more robust paleoclimate reconstructions in semi-arid regions – a case study from Mongolian lake sediments

Bliedtner M¹, Strobel P¹, Struck J¹, Salazar G², Szidat S², Nowaczyk N³, Bazarradnaa E⁴, Lloren R^5,6, Dubois N^5,6, Haberzettl T⁷, Zech R¹

¹Institute of Geography, Friedrich Schiller University Jena, Jena, Germany, ²Department of Chemistry, Biochemistry and Pharmaceutical Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland, ³Section Climate Dynamics and Landscape Evolution, GFZ German Research Centre for Geosciences, Potsdam, Germany, ⁴Institute of Plant and Agricultural Sciences, Mongolian University of Life Sciences, Darkhan, Mongolia, ⁵Department of Surface Waters Research and Management, Eawag, Dübendorf, Switzerland, ⁶Department of Earth Sciences, ETH Zürich, Zürich, Switzerland, ⁷Physical Geography, Institute for Geography and Geology, University of Greifswald, Greifswald, Germany

Semi-arid Mongolia is a highly sensitive region to paleoclimate changes, but the region’s paleoclimatic evolution and its underlying forcing mechanisms have been controversially discussed. In this context, chronological control of the region’s existing paleoenvironmental reconstructions are often imprecise because chronologies are mostly derived from few ¹⁴C-dates on bulk organic material. Bulk organic carbon has often been used in semi-arid regions due to the absence of terrestrial macrofossils. Compared to terrestrial macrofossils, which are assumed to be rapidly deposited in lakes, bulk organic carbon can be “pre-aged” because organic material accumulates in the catchment over hundreds to thousands of years and possibly overestimates the “true” deposition age when ending up in the lake.

Here we present the chronology of a 7.4 ka sediment record for paleoclimate reconstructions from the high-altitude Shireet Naiman Nuur (Nuur = lake)  in the central Mongolian Khangai Mountains. We extensively ¹⁴C-dated bulk organic carbon and terrestrial macrofossils from the lake sediments and provide a robust and precise chronology for the past 7.4 ± 0.3 cal. ka BP, with mostly all ¹⁴C-ages in stratigraphic order. The ¹⁴C-based chronology is confirmed by paleomagnetic secular variations, which resemble the predictions of spherical harmonic geomagnetic field models. The very good chronological control makes paleomagnetic secular variation stratigraphy a powerful tool for evaluating and refining regional ¹⁴C chronologies when compared to our newly obtained record. Based on our good chronological control, we finally reconstructed variations in paleotemperature and paleohydrology based on established sedimentological proxies and innovative compound-specific δ²H analyzes of specific biomarkers.