A Late Glacial Environmental Reconstruction performed on Lacustrine Sediments from the Southern Tibetan Plateau identifies regional Monsoon Variations

Karoline Henkel1, Marieke Ahlborn1, Torsten Haberzettl1, Mauro Alivernini1, Thomas Kasper2, Andrej Thiele3, Guillaume St-Onge4, Gerhard Daut1, Peter Frenzel5, Gerd Gleixner6, Junbo Wang7, Liping Zhu8 and Roland Maeusbacher1, (1)Friedrich Schiller University of Jena, Jena, Germany, (2)Friedrich-Schiller-University, Jena, Germany, (3)Max Planck Institute for Biogeochemistry, Jena, Germany, (4)University of Quebec at Rimouski UQAR, Canada Research Chair in Marine Geology, Rimouski, QC, Canada, (5)Friedrich Schiller University of Jena, Institute of Geosciences, Jena, Germany, (6)Max Planck Institute for Biogeochemistry, Department of Biogeochemical Processes, Jena, Germany, (7)Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China, (8)University of Chinese Academy of Sciences, Beijing, China
Abstract:
The Tibetan Plateau (TP) is very sensitive to climate variations and is therefore an ideal study site to investigate past climate changes. Influenced by the Asian Monsoon system, the numerous lake systems on the TP serve as valuable archives for past hydrological changes, which are assumed to be caused by variations in strength and extent of the monsoonal impact.

The lacustrine record from the terminal lake Tangra Yumco (4540 m a.s.l., 31°13’N, 86°43’E) consists of an interbedding of fine-grained silty sediments with laminations of different thicknesses (sub-mm to cm) and partly intercalated blackish sandy layers. Thin section analysis in the laminated areas reveals cyclic laminations composed of a carbonate and a detrital layer. Homogenous intervals represent turbidite deposits which are further detected based on lithology, radiography as well as changes in the water content, grain size, Ti-values (XRF) and in the paleomagnetic parameter median destructive field.

The chronology is based on 27 AMS-radiocarbon ages on bulk organic matter and one piece of wood, which is of terrestrial origin. To determine a possible carbon reservoir effect, additional surface sediment samples and one modern aquatic plant were measured. The calculated reservoir effect of 2,120 +110/-90 years is assumed to be constant over the time and thus the base of the record reveals a corrected radiocarbon age of 17,270 +325/-310 cal BP. Additionally, investigations on paleomagnetic secular variations were carried out, showing that since 15,900 cal BP the record preserved a well-defined magnetization recording a genuine paleomagnetic signal.

Regarding the geochemical (organic and inorganic), sedimentological, mineralogical and micropaleontological analyses, a low lake level with a high terrestrial input is observed for the Late Glacial. At 15.6 ka cal BP, a change in the sediment accumulation rate, increased allochthoneous input and changing ostracod fauna point to an increasing lake level. In the Early Holocene, a high lake level with a low salinity and low terrestrial input is observed. At 5,000 cal BP, the carbonate phase changes from calcite to aragonite, representing a higher evaporation rate and a falling lake level and a higher influence of terrestrial biomarkers.

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