Method Isotope OH P

Water, the driver of weathering and formation of secondary minerals, is made of two molecules: oxygen and hydrogen. Oxygen and hydrogen are composed of two main isotopes, each, which are 16O (99.76%) and 18O (0.20%), and 1H (99.9%) and 2H (0.01%).
The evaporation of water from a water source (e.g. the ocean) lead to an enrichment of the lightest isotopes as they are more easily evaporated compared to heavy molecules of water. But the relative proportion of these isotopes in water (or isotopic composition) can vary according to the climatic variation.
For example, the evaporation of heavy isotopes is more efficient during warm climatic episodes and thus the rainwater is enriched in heavy isotopes. While formation of secondary minerals, the oxygen and hydrogen isotopic signal of the water source is trapped within the mineral structure and preserved over long period.
It is then possible to measure the O and H isotopic composition of this mineral which may reveal specific climatic conditions.
The different water molecules (USGS)
Oxygen and hydrogen isotopic composition of kaolinites (Al2Si2O5[OH]4) extracted from different weathering profiles, has been investigated to give us further information of the climate during the time of their formation. These measurements have been performed at the Institut de Physique du Globe de Paris (IPGP).