Isotope amount effects in hydrologic and climate reconstructions of monsoon climates: Implications of some long-term data sets for precipitation

Article history: Received 6 May 2015 Received in revised form 16 March 2016 Accepted 19 March 2016 Available online 21 March 2016 Many studies of Quaternary climatemake use of terrestrial stable isotope records which are interpreted based on seasonal patterns of stable isotopes in modern precipitation. Multi-decade records of isotopes in rainfall allow testing of the assumed behavior of isotope signals used for this interpretation on multi-year to decadal scales. A 32-year record of stable O and H isotopes in precipitation in Tucson, Arizona permits a detailed examination of stable isotope amount effects, at time scales ranging from individual events to decades, in a locationwith summer monsoonal andwinter frontal rainy seasons. Amount effects are weak to non-existent in Tucson at seasonal and longer time scales, and are not useful for discriminating eitherwetter or drier rainy seasons orwetter or drier decades. Amount effects are also weak to non-existent in published data for annual and multi-year amountweighted averages for monsoonal precipitation in New Delhi and Hong Kong, but an annual amount effect appears to be present on Guam (U.S. Territory). In addition, site-specific amount effects do not correlate with measures of regional monsoon intensity. This data analysis challenges the general validity of paleoclimate reconstructions based on short-term (sub-annual) relationships observed in precipitation isotope data when applied to long-term records such as speleothem studies. © 2016 Elsevier B.V. All rights reserved.