Continuous monitoring of summer surface water vapor isotopic composition above the Greenland Ice Sheet
We present here surface water vapor isotopic measurements conducted from\nJune to August 2010 at the NEEM (North Greenland Eemian Drilling\nProject) camp, NW Greenland (77.45 degrees N, 51.05 degrees W, 2484 m\na.s.l.). Measurements were conducted at 9 different heights from 0.1m to\n13.5m above the snow surface using two different types of\ncavity-enhanced near-infrared absorption spectroscopy analyzers. For\neach instrument specific protocols were developed for calibration and\ndrift corrections. The inter-comparison of corrected results from\ndifferent instruments reveals excellent reproducibility, stability, and\nprecision with a standard deviations of similar to 0.23 parts per\nthousand for delta O-18 and similar to 1.4 parts per thousand for delta\nD. Diurnal and intraseasonal variations show strong relationships\nbetween changes in local surface humidity and water vapor isotopic\ncomposition, and with local and synoptic weather conditions. This\nvariability probably results from the interplay between local moisture\nfluxes, linked with firn-air exchanges, boundary layer dynamics, and\nlarge-scale moisture advection. Particularly remarkable are several\nepisodes characterized by high (> 40 parts per thousand) surface water\nvapor deuterium excess. Air mass back-trajectory calculations from\natmospheric analyses and water tagging in the LMDZiso (Laboratory of\nMeteorology Dynamics Zoom-isotopic) atmospheric model reveal that these\nevents are associated with predominant Arctic air mass origin. The\nanalysis suggests that high deuterium excess levels are a result of\nstrong kinetic fractionation during evaporation at the sea-ice margin.