A Drop in the Bucket: Hydrometeors and Surface Water / Ice Reservoir Isotope Exchange with the Atmosphere

Isotopologues of water are critical geochemical proxies and tracers used in climatological, meteorological, and hydrological studies. For example, the isotopes deuterium and oxygen-18 within all phases of water act as proxies for paleotemperatures using ice cores, as tracers for identifying groundwater sources, as tracers for freshwater mixing within oceans, and numerous other uses. Isotope fractionation (the partitioning of heavy and light isotopes during phase change) is an important process in the water cycle that generates isotope signals in vapor, liquid, and ice, and allows for their use as proxies and tracers. To first order, isotope fractionation processes are generally well understood; however there remains unresolved questions regarding post-depositional and secondary processes such as isotope fractionation during sublimation of ice and hydrometeor-background atmosphere isotope exchange. In this dissertation, these unresolved questions are explored in three areas. Firstly, the isotope evolution of water droplets as a result of evaporation and atmosphere – water droplet exchange are explored through suspending water droplets in air via acoustic levitation. In this study, the change in isotope composition of the droplet as it was suspended reflected evaporation into a closed or quasi-closed system where the evaporative flux is allowed to re-exchange with the droplet. Secondly, ice spheres were suspended via tees in a cold chamber to study the degree of change in isotope composition as a result of sublimation. In this second study, we propose that small amounts of porosity within the ice spheres increased molecular diffusion within the ice enough to generate the small observed fractionation effect. Finally, we evaluate the effect of meteorological and climatological factors on the ablation of Dry Valley lakes Lake Fryxell and Lake Bonney in Antarctica using water isotopologues. In these energy-limited lake systems, it was observed that during periods of high boundary layer turbulence, isotope fractionation during ablation of surface ice is near zero, while ablation approaches equilibrium fractionation levels during periods of low turbulence, especially at slightly warmer lakes such as Lake Fryxell. The low to near zero fractionation of ice during high turbulence periods at both lakes was consistent with those observations from the ice spheres experiment. The results of this work provide important additional clarification on the behavior of water isotopologues which should be taken into consideration in their use as climatological, meteorological, and hydrological tracers and proxies.