A detailed study of snow accumulation and stable isotope content in Dome C (Antarctica)

International audienceSnow samples have been taken in the Dome C area in order to study the variations of the accumulation rate and of the stable isotope content over the last century. Stake observations indicate a large spatial variability of the accumulation rate at a 1-year scale (σs = 2.6 g cm$^{−2}$ yr$^{−1}$ for a mean value ā = 3.6 g cm$^{−2}$ yr$^{−1}$). The depth of the 1965 and 1955 layers determined from beta radioactivity measurements in 19 sites lets us deduce that the spatial variability becomes small at a 10-year scale (σs = 0.3 g cm$^{−2}$ yr$^{−1}$), showing that the snow collected at one point is well representative of the fallen precipitation over this period. The rate of snow accumulation since 1965 is about 30% higher than during the 1955–1965 period. This conclusion is supported by measurements over a large geographical sector of East Antarctica. Shorter-term changes of the snow accumulation have been studied by various means and in particular from detailed deuterium content profiles; by comparing with the beta and tritium radioactivity determinations it is shown that the deuterium variations do not allow us to obtain a seasonal record. In such a low-accumulation area, different mechanisms (such as smoothing of the isotopic signal, roughness of the surface, irregularity of the accumulation) which may disturb the short-term record are discussed. The interpretation of stratigraphie observations is not straightforward. However, it was possible to obtain a calibration down to the 1955 layer, which allows us to offer a dating of the snow layers over the last century. The mean accumulation so obtained (3.7 g cm$^{−2}$ yr$^{−1}$) is in good agreement with the value (3.6±0.5) deduced from lead 210 measurements. Geographical changes of the mean deuterium content are relatively small, showing that at a 10-year scale the isotopic signal is well representative of the mean deuterium content of the precipitation. This ensures that the smoothed (10-year running mean values) deuterium profile obtained over the last 160 years provides a good indication of the temperature secular trend in the Dome C area