δ 18 O and δD of streamwaters across the Himalaya and Tibetan Plateau: Implications for moisture sources and paleoelevation reconstructions Michael T. Hren a, ⁎, Bodo Bookhagen b , Peter M. Blisniuk c , Amanda L. Booth d , C. Page Chamberlain e a Department of Geology & Geophysics, Yale University, 210 Whitney Ave. New Haven, CT 06511, United States b Department of Geography, University of California Santa Barbara, 1832 Ellison Hall, Santa Barbara, CA 93106-4060, United States c Department of Environmental Earth System Science, Stanford University, 450 Serra Mall, Braun Hall, Building 320, Stanford University, Stanford, CA 94305-2115, United States d Water and Environmental Research Center, Institute of Northern Engineering, University of Alaska, Fairbanks P.O. Box 755860, Fairbanks, Alaska 99775-5860, United States e Department of Environmental Earth System Science, Stanford University, 450 Serra Mall, Braun Hall, Building 320 Stanford University, Stanford, CA 94305, United States abstract article info Article history: Received 22 May 2009 Received in revised form 6 August 2009 Accepted 25 August 2009 Editor: P. DeMenocal Keywords: paleoelevation paleoaltimetry Tibetan Plateau Himalaya isotopes precipitation This study presents new δ 18 O and δD data from 191 streams across the Himalaya and Tibetan Plateau to better constrain the spatial variability of stable isotopes in modern precipitation over this region. Moisture penetrating into the southeastern Tibetan Plateau is predominantly derived from monsoonal airmasses originating from the Bay of Bengal and transported into the eastern Himalayan syntaxis along the Brahmaputra River. Progressive rainout during orographic lifting and cooling results in clear relationships between δ 18 O and δD and catchment hypsometric elevation on the plateau margin. However, monsoonal-derived moisture is progressively mixed with central Asian airmasses in more western and northern parts of the Tibetan Plateau. As a result, predicted isotope–elevation relationships that are based on empirical lapse rates or thermodynamic models of the isotopic evolution of an airmass produce large (1–3 km) misfits between measured and predicted catchment elevations for much of the Tibetan Plateau, including some areas directly north of the central Himalayan crest. This suggests that changes in the δ 18 O or δD of paleoprecipitation on the central and southwestern Tibetan Plateau may reflect surface uplift along moisture transport pathways or changes in the penetration of monsoonally-derived moisture rather than regional surface uplift histories. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Stable-isotope paleoelevation reconstructions of the Tibetan Plateau rely on empirical data or model-based assumptions of the relationship between the Δδ 18 O or ΔδD of precipitation and elevation that can be applied to paleoprecipitation isotope proxy localities (e.g. Garzione et al., 2000a; Rowley et al., 2001; Poage and Chamberlain, 2001). In recent years, a global network for isotopes in precipitation (GNIP) has been established by the International Atomic Energy Agency to monitor long-term patterns and changes in the δ 18 O and δD of global precipitation and relationships with geographical parameters. While this network has provided valuable baseline data on the isotopic composition of global precipitation, large areas such as the Himalaya and Tibetan Plateau are characterized by a single isotope-monitoring station. Thus, paleoenvironmental interpretations of isotopic records in this region commonly rely on global (Bowen and Revenaugh, 2003) or regional (Liu et al., 2008a,b) models of the isotopic composition of precipitation that were derived from relatively few and distal sampling stations. Moreover, model predictions for δ 18 O in high elevation areas with complex moistures sources can deviate from actual site measure- ments by + 5 to -5‰ (Liu et al., 2008a,b), a range that greatly exceeds the variability observed in many paleoisotopic records of Cenozoic change (e.g. Garzione et al., 2000b, 2004; Rowley and Currie, 2006). A number of studies have specifically examined δ 18 O, and to a lesser extent δD, in precipitation and groundwaters from the Himalayan front (e.g. Aizen et al., 1996; Pande et al., 2000; Garzione et al., 2000a; Karim and Veizer, 2002), Tibetan Plateau (e.g. Wushiki, 1981; Yu and Zhang, 1981; Zhang, 1997; Zhang et al., 2002; Tian et al. 2001a, b,c, 2003; Quade et al., 2007), and Southeast Asia (Araguás-Araguás and Froehlich, 1998; Liu et al., 2008a,b) to identify the environmental and geographical controls of the isotopic composition of precipitation in this region. Data from the Himalayan front (Garzione et al., 2000a) and the eastern edge of the Tibetan Plateau (Yu and Zhang, 1981) show a clear relationship between the altitude of groundwater sampling sites and the measured δ 18 O (~0.3‰/100 m elevation) that agrees with global isotope lapse data (Poage and Chamberlain, 2001) and model predictions for the distillation of an airmass during orographic ascent and progressive rainout (Rowley et al., 2001; Rowley, 2007; Rowley and Garzione, 2007). However, stable isotope measurements of precipitation (Tian et al., 2001a,b,c, 2005, 2007, 2008) and groundwaters at sites across the plateau (Yu and Zhang, 1981; Wushiki, 1981; Quade et al., 2007) show strong latitudinal controls on the δ 18 O of water across this region. Earth and Planetary Science Letters 288 (2009) 20–32 ⁎ Corresponding author. E-mail address: mhren@umich.edu (M.T. Hren). 0012-821X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2009.08.041 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl