EPSS Colloquium fall-2017

¹⁸O/¹⁶O ratios are widely used in paleoclimate studies as proxies for temperature, precipitation amount and hydrologic change, but interpretations of these records are often challenged by the multiple factors that can influence them. Variation in ¹⁷O/¹⁶O ratios of Earth materials have long been assumed to co-vary with ¹⁸O/¹⁶O ratios in predictable and uniform ways such that they were not considered useful in studies of Phanerozoic climate. However, recent advances in the ability to measure small differences in D¹⁷O, the deviation from an expected relationship between ¹⁸O/¹⁶O and ¹⁷O/¹⁶O ratios, both in waters and low-temperature materials (e.g., carbonates, bioapatites, silicates, oxides) present the opportunity to use triple oxygen isotope measurements in hydrological and paleoclimate studies. In particular, the sensitivity of D¹⁷O to kinetic fractionation means that it can be used to constrain the influence of kinetic effects on variations in d¹⁸O. In this talk, I will review the growing number of datasets on the triple oxygen isotope composition of the hydrosphere and present an example of how triple oxygen isotopes in lacustrine carbonates can be used to constrain hydroclimate in the past. A compilation of D¹⁷O data from precipitation, which includes snow from polar regions, tropical storms and weekly precipitation collections from mid-latitudes, shows that the D¹⁷O of precipitation can range from -0.06 to +0.07‰. In the western U.S., there are clear seasonal differences in D¹⁷O of precipitation. A continent-wide survey of tap waters from the U.S. mirrors the variation observed in precipitation. Among leaf waters, D¹⁷O values range from -0.28 to +0.04‰ and can vary by as much as 0.16‰ in a plant within a single day. The mass-dependent effects associated with kinetic fractionation are likely responsible for the majority of the observed variation in waters, either during re-evaporation of rainfall in warm climates, snow formation at very cold temperatures, or evapotranspiration. In lakes, variation in D¹⁷O can be used to discern the role of evaporative water loss in the overall water balance. In summary, the combination of the observed variation of D¹⁷O in continental waters and the emerging techniques for measuring D¹⁷O in a wide range of geologic materials means that it is now possible to use D¹⁷O to monitor the effects of kinetic fractionation on meteoric waters and provide additional constraints on variation of d¹⁸O in sedimentary archives.