Late Quaternary hydrological changes inferred from lake level fluctuations of Nam Co (Tibetan Plateau, China) G. Daut a, * , R. Ma ¨ usbacher a , J. Baade a , G. Gleixner d , E. Kroemer c , I. Mu ¨ gler d , J. Wallner c , J. Wang b , L. Zhu b a Institut fu ¨r Geographie, Friedrich-Schiller-Universita ¨t, Lo ¨bdergraben 32, 07743 Jena, Germany b Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China c Bayerisches Landesamt fu ¨r Umwelt, Hof, Germany d Max Planck Institut fu ¨r Biogeochemie, Jena, Germany article info Article history: Available online 20 January 2010 abstract This paper discusses the range of lake level changes, using hydro-acoustic techniques and sediment core data for Lake Nam Co in Central Tibet (China). This second largest Tibetan lake is situated at an elevation of 4718 m a.s.l. Lake level changes with different high stands documented by beach remnants are widespread on the Tibetan Plateau and also in Lake Nam Co. They indicate significant changes in the hydrological system triggered by the monsoonal circulation. Using hydro-acoustic techniques submerged beach remains at approximately 10/15 m, 30 m, 45 m, 70 m and 95 m below present day lake level were detected, indicating a more negative water balance than today. The 10/15 m lake level is dated to an age equal to the Little Ice Age. All deeper lake levels are assumed to have been formed prior to w10000 cal BP. Folded older sediments, detected in the hydro-acoustic profiles indicate a possible larger extent of the glaciers during or prior to the Last Glacial Maximum (LGM). This is followed by a low stand or even by possible desiccation of the entire lake basin during or after the LGM. Ó 2010 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction Changes in the hydrological cycle on the Tibetan Plateau are mainly caused by changes of the monsoon system forcing changes in precipitation and evaporation. Findings from several archives including glacier ice cores (Thompson et al., 2006), terminal moraines (Lehmkuhl et al., 2002), lake sediments (Gasse et al., 1996; Zhu et al., 2008; Mu ¨ gler, 2008) and beach remains (Avouac et al., 1996) suggest strong changes in the hydrological cycle of this region. Prominent lake level changes have been reported from several Tibetan lakes (Avouac et al., 1996; Gasse et al., 1996; An et al., 2000; Lehmkuhl et al., 2002; Yu and Kelts, 2002). Especially in closed basins, lake terraces and beach ridges can be used to trace lake level fluctuations and to quantify changes in the hydrological balance. Thus, lake level changes on the Tibetan Plateau have been often used as an indicator of a change in the monsoon system. However, due to the size of the Tibetan Plateau a consistent picture concerning spatial and temporal variations of the monsoon system is still missing. In Western Tibet, Avouac et al. (1996) identified in the lakes Longmu and Sumxi Co the highest lake level at 230 m above today’s lake level and suggested that this high stand was formed around 6–7.5 ka BP, followed by an abrupt regression of 160 m occurring within just 120 years. This lake level drop has been related to a sudden change in the precipitation–evaporation-balance (p/e- balance) due to cooler climate conditions with decreasing melt water supply from the glaciers. However, lately the high stand on Sumxi Co has been assigned an age of 11–12.8 ka BP by Kong et al. (2007) using cosmogenic 10 Be. This implicates that the wet phase associated with the onset of the monsoon in this region possibly has to be shifted towards the Late Glacial/Early Holocene period. In the northeast of the Tibetan Plateau Yu and Kelts (2002), investi- gating Qinghai Lake, the largest lake of Tibetan Plateau with a present water depth of only 26.5 m, identified a significant lake level low stand at 24.5 m for the time older than 10 ka BP. During the following 2000 years, the lake level oscillated between 24.5 m and 18.5 m due to an increase in the precipitation–evaporation- balance (p/e-balance). The highest p/e-balance is recorded between 7 and 6 ka BP when the water depth of Qinghai Lake reached 12.0 m above the present day lake level. In the Central Tibetan Plateau (Dagce Co and Siling Co) highest lake levels are documented by beach ridges and lake terraces up to * Corresponding author. Tel.: þ49 3641948804; fax: þ49 3641948812. E-mail address: gerhard.daut@uni-jena.de (G. Daut). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint 1040-6182/$ – see front matter Ó 2010 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2010.01.001 Quaternary International 218 (2010) 86–93