The isotopic composition of water vapour and precipitation in Ivittuut, southern Greenland

Since September 2011, a wavelength-scanned cavity ring-down spectroscopy analyser has been remotely operated in Ivittuut, southern Greenland, providing the first record of surface water vapour isotopic composition based on continuous measurements in South Greenland and the first record including the winter season in Greenland. The comparison of vapour data with measurements of precipitation isotopic composition suggest an equilibrium between surface vapour and precipitation. delta O-18 and deuterium excess are generally anti-correlated and show important seasonal variations, with respective amplitudes of similar to 10 and similar to 20 parts per thousand, as well as large synoptic variations. The data depict small summer diurnal variations. At the seasonal scale, delta O-18 has a minimum in November-December and a maximum in June-July, while deuterium excess has a minimum in May-June and a maximum in November. The approach of low-pressure systems towards South Greenland leads to delta O-18 increase (typically + 5 parts per thousand) and deuterium excess decrease (typically - 15 parts per thousand). Seasonal and synoptic variations coincide with shifts in the moisture sources, estimated using a quantitative moisture source diagnostic based on a Lagrangian back-trajectory model. The atmospheric general circulation model LMDZiso correctly captures the seasonal and synoptic variability of delta O-18, but does not capture the observed magnitude of deuterium excess variability. Covariations of water vapour isotopic composition with local and moisture source meteorological parameters have been evaluated. delta O-18 is strongly correlated with the logarithm of local surface humidity, consistent with Rayleigh distillation processes, and with local surface air temperature, associated with a slope of similar to 0.4 parts per thousand degrees C-1. Deuterium excess correlates with local surface relative humidity as well as surface relative humidity from the dominant moisture source area located in the North Atlantic, south of Greenland and Iceland.