Triple oxygen and hydrogen isotopes of gypsum hydration water for quantitative paleo-humidity reconstruction

Atmospheric relative humidity is an important parameter affecting vegetation yet paleo-humidity proxies are scarce and difficult to calibrate. Here we use triple oxygen (delta O-17 and O-18) and hydrogen (delta D) isotopes of structurally -bound gypsum hydration water (GHW) extracted from lacustrine gypsum to quantify past changes in atmospheric relative humidity. An evaporation isotope-mass-balance model is used together with Monte Carlo simulations to determine the range of climatological conditions that simultaneously satisfy the stable isotope results of GHW, and with statistically robust estimates of uncertainty. We apply this method to reconstruct the isotopic composition of paleo-waters of Lake Estanya (NE Spain) and changes in normalized atmospheric relative humidity (RH.) over the last glacial termination and Holocene (from similar to 15 to 0.6 cal. kyrs BP). The isotopic record indicates the driest conditions occurred during the Younger Dryas (YD; similar to 12-13 cal. kyrs BP). We estimate a RHQ of similar to 40-45% during the YD, which is similar to 30-35% lower than today. Because of the southward displacement of the Polar Front to similar to 42 degrees N, it was both windier and drier during the YD than the Belling-Allered period and Holocene. Mean atmospheric moisture gradually increased from the Preboreal to Early Holocene (similar to 11 to 8 cal. kyrs BP, 50-60%), reaching 70-75% RH. from similar to 7.5 cal. kyrs BP until present-day. We demonstrate that combining hydrogen and triple oxygen isotopes in GHW provides a powerful tool for quantitative estimates of past changes in relative humidity. (C) 2017 Elsevier B.V. All rights reserved.