Final Report Summary - WIHM (Water Isotopes of Hydrated Minerals (WIHM))
The main objective of the project was to study hydration water in minerals using newly developed analytical techniques, and apply these methods to studying past environmental conditions. Hydration water in minerals can exist in multiple forms (absorbed, interlayer, structural, hydroxyl) and it is often difficult to separate and independently measure the different component water in a hydrated mineral. We successfully developed new analytical methods to measure the different types of water in minerals (molecular and hydroxyl) with site-specific information that has proven difficult to obtain previously (Bauska et al., 2018). We also developed a bespoke multi-line system to extract total water in minerals at temperatures <450oC (Gazguez et al., 2015). We empirically re-determined fractionation factors between gypsum hydration water and mother water to a greater precision than previously measured, including changes in fractionation factors as a function of temperature and salinity (Gazguez et al., 2017). In WP3, we used first principles to theoretically calculate the fractionation factors based on density functional theory (Liu et al., 2018). The excellent agreement between the theoretical and empirical fractionation factors provides much confidence in the results.
We applied the new technique to a series of field-based studies to test the use of mineral hydration water for palaeoenvironmental reconstruction. We conducted a set of wide-ranging application studies, including: (i) development of the use of triple oxygen and hydrogen isotopes of gypsum hydration water for estimating past changes in relative humidity and precipitation (Gazguez et al., 2018); (ii) application of this new method provided quantitative estimates of past changes in rainfall on the Yucatan Peninsula, Mexico, at the time of the collapse of Classic Maya Civilization (Evans et al., 2018); (iii) the method was also applied to dry palaeo-lake Karsandi in NW India to reconstruct changes in the intensity of the Indian monsoon, and how it relates to development and migration of the Indus Valley Civilisation (Dixit et al., 2018); (iv) measurement of gypsum hydration water in the Sorbas Basin, Spain, has documented the influence of meteoric water during the deposition of the lower evaporites during the late Miocene Messinian Salinity Crisis (Evans et al., 2015); (v) we have also applied the method to understand the controls on the formation of caves and gypsum speleothems (Gazguez et al., 2017b, 2019). This fundamental information will form the basis for using gypsum speleothems to reconstruct palaeoclimate records, which is novel because speleothem studies have thus far been limited to carbonates; (vi) lastly, we have combined oxygen isotope measurements 18O and ΔO47) of gypsum hydration with cogenic carbonates to uniquely predict past temperature changes (Grauel et al., 2016; Gazguez et al., 2018).
We applied the new technique to a series of field-based studies to test the use of mineral hydration water for palaeoenvironmental reconstruction. We conducted a set of wide-ranging application studies, including: (i) development of the use of triple oxygen and hydrogen isotopes of gypsum hydration water for estimating past changes in relative humidity and precipitation (Gazguez et al., 2018); (ii) application of this new method provided quantitative estimates of past changes in rainfall on the Yucatan Peninsula, Mexico, at the time of the collapse of Classic Maya Civilization (Evans et al., 2018); (iii) the method was also applied to dry palaeo-lake Karsandi in NW India to reconstruct changes in the intensity of the Indian monsoon, and how it relates to development and migration of the Indus Valley Civilisation (Dixit et al., 2018); (iv) measurement of gypsum hydration water in the Sorbas Basin, Spain, has documented the influence of meteoric water during the deposition of the lower evaporites during the late Miocene Messinian Salinity Crisis (Evans et al., 2015); (v) we have also applied the method to understand the controls on the formation of caves and gypsum speleothems (Gazguez et al., 2017b, 2019). This fundamental information will form the basis for using gypsum speleothems to reconstruct palaeoclimate records, which is novel because speleothem studies have thus far been limited to carbonates; (vi) lastly, we have combined oxygen isotope measurements 18O and ΔO47) of gypsum hydration with cogenic carbonates to uniquely predict past temperature changes (Grauel et al., 2016; Gazguez et al., 2018).