Acknowledgments
We gratefully acknowledge Karin Schmidt, Anita Kriegel, Susann Enzmann and Ingrid Ostermeyer for their careful help with laboratory and fieldwork. We thank the Laboratory for Radioisotopes (LARI) and Centre for Stable Isotope Research and Analysis (KOSI) of the University of Göttingen. We would also like to thank China Scholarship Council for the fellowship for Yue Sun and Huadong Zang, and the DAAD scholarship award to Amit Kumar.