Ice volume as a trigger for the amplification of Pleistocene millennial-scale climate fluctuations? A terrestrial perspective from Central Asia (Qaidam Basin)
Final Report Abstract
The principal objective of this project was to understand millennial-scale climate variability during the Late Pliocene to Early Pleistocene intensification of northern hemisphere glaciation (iNHG) by tackling this issue from a new, different angle, i.e., via terrestrial archives. The project was designed to study records that are under the direct influence of northern hemisphere ice sheets (i.e., the influence of the East Asian Winter Monsoon; EAWM) on Central Asia using a drillcore record with high sedimentation rates from the Qaidam Basin (Core Sg-1b; NE Tibetan Plateau). Overall, the project followed the proposed framework but some modifications to the overall objectives and working program as outlined in the original proposal were necessary, mainly related to the successful testing of XRF core scanning for the studied core material. This dataset fueled the establishment of an astrochronological age model. Using information from grain-size analyses, the ln(Rb/Sr) ratio derived from XRF core scanning has been demonstrated as a faithful recorder of fluctuations in moisture availability and used to tie wet-dry alternations to obliquity-paced glacial/interglacial cycles. Superimposed on the obliquity forcing we find indications for obliquityprecession interferences during the late Pliocene (~3.3–3.0 Ma). Our results also suggest that a long-term decrease in sedimentation rate in Core SG-1b from the late Pliocene to the early Pleistocene mirrors the previously reported increasing aridification of Central Asia. The established age model allowed the comparison of the Qaidam Basin records with the marine isotope stratigraphy, hence enabling the study of the sedimentological data produced in this project (i.e., grain size and loss of ignition (LOI) variability) within the context of glacial/interglacial cycles. Our new high-resolution LOI and grain-size records from Core SG-1b show pronounced glacial/interglacial climate fluctuations that have occurred on the NE Tibetan Plateau during the latest Pliocene and early Pleistocene and therefore infer a link between the observed glacial/interglacial climate fluctuations with the waning and waxing of ice sheets across the iNHG. Close accordance between the SG-1b record with the LR04 stack, Earth’s orbital parameters, and the Chinese loess record suggests that iNHG is the primary driver of the observed glacial/interglacial climatic fluctuations through its influence on the Siberian High-pressure system and, in turn, the EAWM. The characterization of the nature and tempo of millennial-scale climate fluctuations and their comparison to the well-known Late Pleistocene millennial-scale variability is still ongoing. The established high-resolution XRF dataset as well as the sedimentological data, however, clearly show the occurrence of millennial-scale events and allow to tackle this objective of the project in the near future. In addition to the above-mentioned sedimentological/geochemical work on the Plio/Pleistocene interval, a long-term palynological record from the Qaidam Basin has been established for the last 7 Ma. Integration of our palynological data from the Qaidam Basin with Northern Hemisphere climate-proxy and regional-scale tectonic information suggests that the uplift of the Tibetan Plateau posed ecological pressure on Central Asian plant communities, which made them susceptible to the effects of early Northern Hemisphere glaciations during the late Pliocene. Although these glaciations were relatively small in comparison to their Late Pleistocene counterparts, the transition towards drier/colder conditions pushed previously existing plant communities beyond their tolerance limits, thereby causing a fundamental reorganization of arid ecosystems.
Publications
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(2019): Late Pliocene vegetation turnover on the NE Tibetan Plateau (Central Asia) triggered by early Northern Hemisphere glaciation. Global and Planetary Change 180: 117-125
Koutsodendris, A., Allstädt, F.J., Kern, O.A., Kousis, I., Schwarz, F., Vannacci, M., Woutersen, A., Appel, E., Berke, M.A., Fang, X., Friedrich, O., Hoorn, C., Salzmann, U. & Pross, J.
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(2020): A late Pliocene to early Pleistocene (3.3-2.1 Ma) orbital chronology for the Qaidam Basin paleolake (NE Tibetan Plateau) based on the SG-1b drillcore record. Newsletters on Stratigraphy 53: 479-496
Kaboth-Bahr, S., Koutsodendris, A., Lu, Y., Nakajima, K., Zeeden, C., Appel, E., Fang, X., Rösler, W., Friedrich, O. & Pross, J.
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(2020): Sedimentological evidence for pronounced glacialinterglacial climate fluctuations on NE Tibet in the latest Pliocene to early Pleistocene. Paleoceanography & Paleoclimatology 35: e2020PA003864
Lu, Y., Dewald, N., Koutsodendris, A., Kaboth-Bahr, S., Rösler, W., Fang, X., Pross, J., Appel, E. & Friedrich, O.
