Triple Oxygen Isotopes In The Water Cycle

The past decade has seen a remarkable expansion of studies that use mass-dependent variations of triple oxygen isotopes (O-16, O-17, O-18) in isotope hydrology and isotope geochemistry. Recent technological and analytical advances demonstrate that small deviations of delta'O-18 and delta'O-17 from a mass-dependent reference relationship are systematic and are explained by well-known equilibrium and kinetic fractionations. Measurements of delta'O-18 and delta'O-17 complement traditional metrics like deuterium-excess, constrain isotope effects of kinetic fractionation that are impossible to discern with delta'O-18 alone, and help reconstruct past environmental conditions from geologic records. In this review, we synthesize published meteoric (derived from precipitation) water triple oxygen isotope data with a new, near-global surface water dataset of delta'O-18, delta'O-17, delta H-2, deuterium-excess, and Delta'O-17, where Delta'O-17 is defined as delta'O-17-lambda(ref) delta'O-18, delta' notation is a logarithmic definition of the common d value (delta'=ln( delta + 1), and.ref is equal to 0.528. The expanded dataset shows that meteoric water delta' O-18 and delta'O-17 fit multiple regression lines and indicates that one global meteoric water line does not adequately describe all triple oxygen isotope data. Instead, this isotope system may be sensitive to processes such as moisture transport, rainout, and evaporation that do not affect the water cycle equally across the globe. This review provides a practical guide to understand Delta'O-17 variation in waters, explains the utility of this isotope system in hydrologic and paleoclimate studies, and outlines directions of future work that will expand the use of Delta'O-17.