Queen's University

Using stable isotopes as windows into the geologic past and as tracers of contemporary environmental processes

The fractionation of stable isotopes during chemical reactions has long been recognized as a tool to trace a variety of geologic processes (e.g., evaporation, mineral dissolution and precipitation), and as a window into the geochemical conditions in the geologic past (e.g., temperature, ocean pH). Advances in analytical techniques have recently allowed measurement of the isotopes of a wider variety of elements, but the processes that control the fractionation of these isotopes and the degree of fractionation incurred during different reactions (represented by the fractionation factor) remain largely undefined. Moreover, in order to use the isotopic signature of a mineral to infer information regarding the environmental conditions at the time of its formation, the signature must not have been altered between the time of mineral formation and the time of measurement, which might be thousands of years or more. Therefore the processes that act to alter isotopic signatures after a mineral has formed, and the magnitude by which they may alter these signatures must be well-known. My ongoing research explores the controls on stable isotopic fractionation (e.g., Mg, C, O, Ca) in carbonate minerals, and the degree to which isotopic signatures may be reset due to isotope exchange at chemical equilibrium. Future work will examine the utility of Mg, Si, Fe, and Ca isotopes as tracers of engineered carbon storage efforts, and the mechanisms that control isotopic signatures in water-limited environments. Together, this research will help develop improved interpretations of isotopic signatures and the processes and environmental conditions they genuinely reflect.