Late Holocene relative humidity history on the southeastern Tibetan plateau inferred from a tree-ring d 18 O record: Recent decrease and conditions during the last 1500 years Jussi Grießinger a, * , Achim Br € auning a , Gerhard Helle b , Philipp Hochreuther a , Gerhard Schleser b, c a Friedrich-Alexander-University Erlangen-Nürnberg, Institute of Geography, Wetterkreuz 15, D-91058 Erlangen, Germany b GFZ German Research Centre for Geoscience, Section 5.2 Climate Dynamics and Landscape Evolution, Telegrafenberg, D-14773 Potsdam, Germany c FZJ Research Centre Jülich, Institute of Bio- and Geosciences IBG-3, Wilhelm-Johnen-Straße, D-52428 Jülich, Germany article info Article history: Available online xxx Keywords: Tree-ring d 18 O Tibetan plateau Relative humidity Summer monsoon 1500 year climate reconstruction Climate variability abstract In recent decades, the Tibetan plateau (TP) experienced a distinctive temperature increase, with fundamental consequences for the hydrological system. As meteorological time-series extending back more than 60 years are scarce, there is a strong need for proxy data providing insight into the regional hydroclimatic history as well as the long-term variability. Within this study, a recently developed annually resolved 1500 year-long tree-ring stable oxygen isotope (d 18 O) time from the southeastern TP is presented. Climateeproxy relationships reveal a strong impact of relative humidity (rH) during the summer months (May to September) on tree-ring d 18 O, explaining around 45% of its variance. The derived reconstruction of relative humidity reveals a recent trend towards drier conditions on the TP. However, the present low rH level is not unprecedented in regard to the last 1500 years. In comparison to recent climate conditions, the Medieval Warm Period (MWP) was characterized by more stable condi- tions with higher humidity values. Hydroclimatic conditions during the Little Ice Age (LIA) suggest a contrasting two-phased period, with a clear shift from drier conditions prevailing between 1400 and 1650 AD to more humid conditions since the second half of the 17th century. Comparisons with other local proxies from lake levels and Pollen data from the southern part of the Tibetan plateau indicate a common regional climate forcing during the MWP and the LIA which can be related to changes in summer monsoon activity. However, the strength of the distinct dryness trend during the 20th century seems unique. © 2016 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction The Tibetan Plateau (TP) is affected by a strong contempora- neous warming trend attributed to the recent climate change (Wei and Fang, 2013). However, beside temperature increase, changes in the hydrological budget are of extreme relevance for affected high- elevation ecosystems (Immerzeel, 2010). By using different paleo- climate proxies such as ice cores, peat bogs, stalagmites or tree-rings, long-term changes of past hydroclimatic variability and intensity on the Tibetan plateau (TP) have been reconstructed (e.g. Dykoski et al., 2005; Gou et al., 2010; Grießinger et al., 2011; Liu et al., 2014). Among these proxies, investigations based on tree rings have made a significant contribution to late Holocene high- resolution paleoclimatology (e.g. Yang et al., 2014). Especially, sta- ble oxygen isotopes in tree rings are gaining growing interest and can be used to reconstruct regional hydrological history on sub- annual to multi-centennial timescales. The isotopic d 18 O signal in tree-ring cellulose is strongly influenced by soil water, which is dependent on the amount and origin of meteoric (precipitation) water (Dansgaard, 1964). While d 18 O of soil water is isotopically unaltered during root uptake, isotopic signature of xylem water is modified at the leaf level by atmospheric temperature and relative humidity before being incorporated in plant photosynthates. Hence, tree-ring cellulose d 18 O can record changes of past climate conditions through its interlink between atmosphere and biosphere (Gessler et al., 2014). As a result of its geographical extent, elevation, and position within the global circulation system, the TP plays a key role in regional and global atmospheric circulation patterns. Climatic * Corresponding author. E-mail address: jussi.griessinger@fau.de (J. Grießinger). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint http://dx.doi.org/10.1016/j.quaint.2016.02.011 1040-6182/© 2016 Elsevier Ltd and INQUA. All rights reserved. Quaternary International xxx (2016) 1e8 Please cite this article in press as: Grießinger, J., et al., Late Holocene relative humidity history on the southeastern Tibetan plateau inferred from a tree-ring d 18 O record: Recent decrease and conditions during the last 1500 years, Quaternary International (2016), http://dx.doi.org/10.1016/ j.quaint.2016.02.011