Closing the Isotope Hydrology at Summit: Measurements of Source Regions, Precipitation and Post-deposition Processes

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The stable isotopic records from the Greenland Ice Sheet are the gold standard for understanding climate variations in the Arctic on decadal to millennial scales. While the basic tenets that underlie interpretation of isotopic information appear robust in a mean sense, meteorological and glaciological processes can confound simple interpretations. Processes of concern are variations in moisture sources, cloud processes, surface ablation, blowing snow and vapor diffusion in the firn. The project objectives are to resolve fundamental uncertainties in the controls on the isotopic composition of the ice sheet through a 3-year measurement campaign at Summit, Eureka and Reykjavik. The project will use measurements and modeling to evaluate 1) the degree to which oxygen isotopic composition and deuterium excess of snow capture variations in moisture sources versus cloud microphysical conditions, and 2) the degree to which blowing snow and vapor diffusion within the firn confound accurate interpretation of variability in the isotopic record. Continuous measurements of the isotopic composition of water vapor and daily measurements of the isotopic composition of freshly-fallen and blowing snow will be made at Summit, Eureka and Reykjavik. These will be combined with measurements of the amount, size distribution, and approximate habit of falling and blowing snow, turbulence measurements to evaluate snow lofting, surface latent heat flux (ablation and frost) and energy balance, and remote sensing of polar clouds and atmospheric structure. High-resolution firn cores will be drilled to reconcile the detailed isotopic measurements and modeling with glaciological records. The new isotope measurements will jump start an emerging international pan-Arctic cooperative network of isotope measurements, which complements Arctic observations under existing Arctic Observing Network activities. The advanced measurements at Summit enhance the site as a comprehensive observatory for monitoring and understanding Arctic change.