Triple oxygen and hydrogen isotopes of gypsum hydration water: A resurrected proxy of hydrologic change

Many minerals incorporate water directly into their structure as molecular water (H₂O) or hydroxyl (OH). The oxygen (16O,17O,18O) and hydrogen (H,D) isotopes of hydrated minerals are a potentially rich source of information about the environmental conditions under which hydrated minerals form and/or interact with fluids after deposition. As part of a 5-year European Research Council project, my group has been developing the use of triple oxygen and hydrogen isotopes of structural water contained in hydrated minerals as a paleoclimate proxy. We are pioneering new methods for measuring d18O, d17O and dD in hydrated minerals by combining thermal gravimetric analysis and cavity ring-down laser spectroscopy. I will specifically discuss the merits and uncertainties in combining measurements of d18O of biogenic carbonates and triple oxygen and hydrogen isotopes of hydration water in gypsum (CaSO₄·H₂O) in lake sediments cores to estimate past changes in temperature, rainfall and relative humidity on the Yucatan Peninsula, Mexico.