Continuous measurements of atmospheric water vapour isotopes in Western Siberia (Kourovka)

Abstract

Abstract. The isotopic composition of atmospheric water vapour at the land surface has been continuously monitored at the Kourovka astronomical observatory in Western Siberia (57.037° N, 59.547° E, 300 m a.s.l.) since April 2012. These measurements provide the first record of δD, δ18O and d-excess in this region. Air was sampled at 8 m height within a forest clearing. Measurements were made with a Wavelength-Scanned Cavity Ring Down Spectroscopy analyzer. A specific protocol was developed for calibration and drift corrections with a particular enhancement to ensure reliable measurements at low humidity during winter. The isotopic measurements conducted till August 2013 exhibit a clear seasonal cycle with maximum δD and δ18O values in summer and minimum values in winter. In addition, considerable synoptic timescale variability of isotopic composition was observed with typical variations of 50–100‰ for δD, 10–15‰ for δ18O and 2–8‰ for d-excess. The strong correlations between δD and local meteorological parameters (logarithm-of-humidity and temperature) are explored, with a lack of dependency in summer that points to the importance of continental recycling and local evapotranspiration. The overall correlation between δD and temperature is associated with a slope of 3‰ °C−1. Large d-excess diurnal variability was observed during summer with up to 30‰ depletion during the night and the minima manifested shortly after sunrise. The accuracy of the isotopic measurements was quantified as 1.4–11.2‰ for δD and 0.23–1.84‰ for δ18O depending on the humidity.