Stable water isotope measured on Col du Dôme and Colle Gnifetti ice cores

In the European Alps, ice core studies have been mainly performed in view of the recent man-made influence on the atmospheric load of aerosol-related species, while respective investigations on the pre-industrial aerosol or on stable water isotope-based climate records remained sparse. We address from a glaciological perspective the specific conditions of Alpine drilling sites and, in particular, the role of depositional noise. Thereby, we refer to two major drilling areas (located in the summit range of Monte Rosa and Mt Blanc massif, respectively) which largely differ in their snow accumulation rate and, hence, in their accessible time scale. A simple scheme considering the seasonality of both, the precipitation-borne signal and the snow erosion-controlled net accumulation rate is presented. It shows that water isotope trends are generally more sensitive to distortion by a seasonality effect than recent snow impurities trends, although the influence of a given seasonal accumulation rate cycle on the mean levels of water isotopes and impurities is similar. These findings are illustrated on the decadal and centennial time scale by the inter- and intra-site variability of major ion and water isotope records. The intra-site comparison includes the discussion of strong water isotope depletions seen some meters above bedrock at low accumulation drilling sites