Exploring the potential of 17O-excess in ice to constrain post-depositional alteration and loss by sublimation.
Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
Final Report Abstract
Over the course of this study, we were able to demonstrate for the first time the validity of the fundamental Craig-Gordon isotope evaporation model in nature for the triple-oxygen isotope system under conditions of evaporation from lakes without recharge, and with recharge. This was demonstrated on lakes from the Sistan Desert (Iran) and Atacama Desert (Chile) over large salinity gradients, that exactly reproduced model expectations at the given climate boundary conditions. Evaporation causes residual water to evolve away from the Global Meteoric Water Line (GMWL) along trajectories that depend mainly on relative humidity, the isotopic composition of initial water, and the isotopic composition of ambient water vapor. These trajectories cannot be seen in plots of δ17O over δ18O because effects are too small to see, but are best observed in a plot of 17O-excess over δ18O, where 17O-excess quantifies the deviation from the GMWL. These two principal types of evaporation cannot be resolved in the classic δ2H-δ18O system, as evaporation trajectories observed in plots of d-excess over δ18O are indistinguishable from each other. This constitutes a significant advantage of the triple oxygen isotope system. We then conducted two field campaigns on the Zugspitze Massiv to investigate and quantify snow and ice sublimation over large snow and ice fields. Based on the fundamental systematics of evaporation summarized above, along with the use of weather data monitoring, and back-tracking of air transport pathways, we were able to model the respective contributions of rain out and continental vapor recycling along the moisture path, and local sublimation / evaporation from snow and ice fields in total atmospheric moisture on the Zugspitze Massiv. Again, these aspects cannot be resolved in much clarity in the classic δ2H-δ18O system. Since not much was known about the triple oxygen isotope evaporation systematics at the start of this project, some of our initially stated objectives quickly became obsolete and were not carried out mostly because of developments during the course of this study led to more important findings. For example, our freezing experiments conducted very early did not yield significant kinetic isotope effects. As such, and for time constraints, we abandoned the analysis of the ice profile from Scarisoara Ice Cave, Romania. An intitial survey of samples from this cave did not produce significant deviations in the 17O-excess parameter despite clear variability in δ18O.
Publications
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(2015). Triple oxygen isotope signatures in evaporated water bodies from the Sistan Oasis, Iran. Geophysical Research Letters, 42
Surma, Assonov, Bolourchi, Staubwasser
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(2018). The evolution of O-17-excess in surface water of the arid environment during recharge and evaporation. Scientific Reports, 8, Article Number 4972
Surma, Assonov, Herwartz, Voigt, Staubwasser
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(2021), Triple Oxygen Isotope Systematics in the Hydrologic Cycle. Reviews in Mineralogy & Geochemistry, 86, 401-428
Surma, Assonov, Staubwasser
