Response of dD values of sedimentary n-alkanes to variations in source water isotope signals and climate proxies at lake Nam Co, Tibetan Plateau F. Günther a , I. Mügler a, 1 , R. Mäusbacher b , G. Daut b , K. Leopold c , U.C. Gerstmann c , B. Xu d , T. Yao d , G. Gleixner a, * a Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, 07745 Jena, Germany b Friedrich Schiller University, Jena, Germany c Helmholtz Zentrum Munich, Germany d TEL, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China article info Article history: Available online 21 December 2010 abstract Compound-specific dD values of sedimentary n-alkanes from Nam Co were compared with oxygen isotope values from three different ice cores of the Tibetan Plateau and other climate proxies including temperature and solar radiation. This enabled estimation of the importance of source water and of environmental factors at the ecosystem scale on variations of the isotopic composition of sedimentary n-alkanes. The ice core records from Dasuopu, Puruogangri and Rongbuk glacier of the past 1000 years recording the source water isotopes show a continuous deuterium enrichment indicating a warming trend or decreased precipitation. Sedimentary n-alkane dD values also represent the same general tendency to enrichment in heavier isotopes. However, the correlation to the d 18 O values derived from the ice record is very weak. The dD values of n-alkanes agree with known climatic events such as the Little Ice Age and Medieval Warm Period showing depleted and enriched dD values, respectively. The dD values of the n-alkanes were best related to environmental drivers including temperature and solar radiation. The results suggest that dD values of sedimentary n-alkanes mainly record evapotranspiration and relative humidity that strongly influence dD values at the plant level, while variability of the source signal is less important. Ó 2010 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction The Tibetan Plateau is one of the major drivers of the global climate and is very sensitive to climatic changes (Kutzbach et al.,1989; Liu and Yang, 2003). It is located at the intersection of the Asian monsoon and Westerlies. At present, the air masses of the Tibetan Plateau mainly originate from moist, warm air from the Indian and Pacific summer monsoon providing the main part of precipitation to this region (Fig. 1). During winter, cold and dry polar air reaches the Plateau (winter monsoon). In addition, the western Tibetan Plateau is influenced by returning westerly winds (Araguás-Araguás et al.,1998; Tian et al., 2007). The southern part of the Plateau, between the Himalaya Mountains and the Tanggula mountains, is dominated by the Indian monsoon that is transported from the Bay of Bengal along the BrahmaputraeYalongzangbo river valley, while in the most northern regions precipitation is delivered by continental moisture recycling (Tian et al., 2001). During the past, the boundaries of these air masses and monsoon intensity have changed, and the Tibetan Plateau is a suitable area to study changes in the past environmental conditions, especially the Asian monsoon history and the hydrological cycle. Alternating monsoonal circulation over the Tibetan Plateau causes hydrological changes and affects the stable isotope content of precipitation. This study focuses on lake Nam Co, assumed to be influenced mainly by the Indian monsoon. It compares different climate proxies including dD values from sedimentary n-alkanes and d 18 O values from different ice cores with environmental drivers including temperature and solar radiation. Ice cores capture the isotopic signature from precipitation within the ice. The controlling factors for variations in d 18 O values are mainly temperature, precipitation and alternating water sources. The isotopic variability in areas above approximately 35  N seem to be mainly driven by temperature, while in southern regions the amount of precipitation is the controlling parameter (Araguás-Araguás et al., 1998; Johnson and Ingram, 2004). Besides ice cores, lacustrine sediments are another archive of climate and environmental change. They preserve aquatic and terrestrial records of environmental conditions within the deposi- ted organic matter. This organic matter in lake sediments contains individual molecular fossils, so-called biomarkers, which are derived * Corresponding author. E-mail address: gerd.gleixner@bgc-jena.mpg.de (G. Gleixner). 1 Present address: University of Washington, Seattle, USA. Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint 1040-6182/$ e see front matter Ó 2010 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2010.12.006 Quaternary International 236 (2011) 82e90