Isotopic exchange on the diurnal scale between near-surface snow and lower atmospheric water vapor at Kohnen station, East Antarctica
Abstract. Quantifying the magnitude of post-depositional processes affecting the isotopic composition of surface snow is essential for a more accurate interpretation of ice core data. To achieve this, high temporal resolution measurements of both lower atmospheric water vapor and surface snow isotopic composition are required. This study presents the first continuous measurements of water vapor isotopes performed in East Antarctica (Kohnen station) from December 2013 to January 2014 using a laser spectrometer. During our monitoring period, the synoptic variability of the water vapor isotopic composition is found to be low compared to the diurnal cycle and we therefore concentrate our study on interaction between the isotopic composition of the vapor and the snow surface on a diurnal timescale. The peak-to-peak amplitude of the snow surface isotopic composition over 24 h reaches 3 ‰ for δD, in phase with the diurnal variations of δD in surface vapor, which itself has an amplitude of 36 ‰. A simple box model treated as a closed system has been developed to study the exchange of water molecules between an air and a snow reservoir. In the vapor, the simulations show too much isotopic depletion compared to the observations. Mixing with other sources (wind advection, free troposphere) has to be included in order to fit the observations. At the snow surface, the simulated isotopic values are close to the observations with a snow reservoir of ∼5 mm depth (range of the snow sample depth). Our analysis suggests that vapor-snow exchanges can no longer be considered insignificant for the isotopic composition of near surface snow in central Antarctica.