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

Abstract

Abstract. Since September 2011, a Wavelength-Scanned Cavity Ringdown Spectroscopy analyzer has been remotely operated in Ivittuut, southern Greenland, providing the first continuous record of surface water vapour isotopic composition (δ18O, δD) in South Greenland and the first record including the winter season in Greenland. This record depicts small summer diurnal variations. Measurements of precipitation isotopic composition suggest equilibrium between surface vapour and precipitation. The vapour data show large synoptic and seasonal variations corresponding to shifts in moisture sources estimated using a quantitative moisture source diagnostic. The arrival of low pressure systems towards south Greenland leads to δ18O enrichment (+5‰) and deuterium excess depletion (−15‰), coupled with moisture sources shifts. Monthly δ18O is minimum in November–December and maximum in June–July, with a seasonal amplitude of ~10‰. The strong correlation between δ18O and the logarithm of local surface humidity is consistent with Rayleigh distillation processes. The relationship with local surface air temperature is associated with a slope of ~0.4‰ °C−1. During the summer 2012 heat waves, the observations display a divergence between δ18O and local climate variables, probably due to the isotopic depletion associated with long distance transport from subtropical moisture sources. Monthly deuterium excess is minimum in May–June and maximum in November, with a seasonal amplitude of 20‰. It is anti-correlated with δ18O, and correlated with local surface relative humidity (at the station) as well as surface relative humidity in a North Atlantic sector, south of Greenland and Iceland. While synoptic and seasonal variations are well represented by the Atmospheric General Circulation Model LMDZiso for Ivittuut δ18O, the model does not capture the magnitude of these variations for deuterium excess.