Modern and Ancient Precipitation  18 O and  D Gradients on the Tibetan Plateau - or - When did the Plateau Plateau? Pratigya J. Polissar 1, Katherine H. Freeman 1, David B. Rowley 2, Brian S. Currie 3 1 The Pennsylvania State University, University Park PA 2 The University of Chicago, Chicago IL 3 Miami University, Oxford OH

Cenozoic Climate Evolution data from Kroon et al. (1991) Quade & Cerling (1995) Clift et al. (2002) Ma et al. (1998) Donghuai et al. (1998) Guo et al.(2002, 2004) Clift (2006)

Plateau Evolution

Stable Isotope Paleoaltimetry

Rowley (2007)

Modern Precipitation Gradient Polissar et al. (in review)

Modern Precipitation Gradient Polissar et al. (in review)

Moisture Source SW Monsoon Westerly after Tian (2007)

Determined by: Moisture source Rainout (airmass trajectory) Moisture recycling Modern Isotope Gradient

Paleowater  18 O and  D  18 O carb : lacustrine, pedogenic, cement New Approach: paired  18 O carb and  D organic

Paleopreciptation Sites Quade et al. (1995); Garzione et al. (2000) ; Dettman et al. (2003); Currie et al. (2005); Cyr et al. (2005); Graham et al. (2005); Rowley & Currie (2006); deCelles et al. (2007); Rieser et al. (2008)

Modern Polissar et al. (in prep.) Modern

Miocene Polissar et al. (in prep.) Miocene

Oligocene Polissar et al. (in prep.) Oligocene

Eocene Polissar et al. (in prep.) Eocene

Observations Modern and past gradients are similar Miocene precipitation isotopes more negative on plateau, no change at edge

Conclusions Topographic barrier to S-N atmospheric circulation has existed since Eocene Present topography in south and central plateau largely developed by Miocene

Implications S. Tibet paleoaltimetry works N. Tibet more complicated - mixed moisture source –similar gradient present throughout Cenozoic despite changing latitude and elevation Essential to understand moisture sources and trajectories on N. plateau

Acknowledgements Canadian Institute for Advanced Research U.S.-National Science Foundation Penn. State Organic Geochemistry Lab (esp. Denny Walizer)

Seawater  18 O Billups & Schrag (2003) –16 – ~  D seawater

Paired  18 O carb and  D organic ModernAncient Polissar & Freeman (in prep.); Polissar et al. (in review)

Cenozoic Polissar et al. (in prep.) Cenozoic