Exploring the potential of 17O-excess in ice to constrain post-depositional alteration and loss by sublimation.

• Applicant: Professor Dr. Michael Staubwasser
• Subject Area: Mineralogy, Petrology and Geochemistry ; Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 266640734

The use of common stable isotope ratios of water (D/H, 18O/16O) in low and mid-latitude snow and ice deposits for budgeting water resources from mountain glaciers and for paleoclimate reconstruction from ice cores is currently limited by the complexity of isotope fractionation reactions occurring after deposition. Post-depositional loss due to sublimation is perhaps the most widely recognized process that modifies the isotopic composition of snow and ice. Such post-depositional modification by sublimation - and by other processes, such as melting-refreezing cycles - are difficult to correct for using the conventional H and O isotope systems because of a dependency of isotope fractionation on temperature. The 17O-excess parameter - similar to d-excess derived from deltaD and delta18O - calculated from the triple O-isotope system (16O-17O-18O), is nearly insensitive to temperature changes in the typical range found on the earth's surface. This allows to identify kinetically controlled isotope exchange, for example during evaporation, without having to consider temperature dependent equilibrium fractionation. We propose to determine triple O-isotope fractionation factors and the evolution of 17O-excess during sublimation and melting-freezing in a series of carefully designed laboratory experiments. We then seek to test the general applicability of 17O-excess to constrain secondary isotopic alteration of snow and ice in the natural high-altitude environment - at Schneefernerhaus research station, German Alps - by a high-resolution monitoring study over a few two-week-long intervals, complemented by regular low resolution snow sampling over the course of a year. Finally, we seek to investigate the most recent ice from the well dated holocene cave ice deposit at Scarisoara ice cave, Romania, with the objective to constrain by 17O-excess the post-depositional isotopic alteration of ice during the annually occurring melting-refreezing cycles that currently hampers the use of stable H and O isotope ratios as paleoclimatic proxies at this location.

• DFG Programme: Research Grants
• International Connection: Austria, USA
• Cooperation Partners: Dr. Sergey Assonov; Professor Bogdan Onac