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.

在欧洲阿尔卑斯山区，冰芯研究此前主要围绕近期人为活动对气溶胶相关物种大气载荷的影响展开，而针对前工业时代气溶胶或以稳定水同位素（stable water isotope）为基础的气候记录的相关研究仍较为匮乏。本研究从冰川学视角出发，探讨阿尔卑斯冰芯钻探点位的特定条件，尤其是沉积噪声（depositional noise）的作用。为此，我们选取两处主要钻探区域（分别位于罗萨峰（Monte Rosa）主峰带与勃朗峰（Mt Blanc）地块），二者的积雪积累率差异显著，因此可获取的时间尺度也各不相同。本研究提出了一套简易模型，同时考虑了降水携带的信号与积雪侵蚀调控的净积雪积累率的季节变化特征。研究结果表明，尽管给定的季节积累率周期对水同位素与杂质平均浓度的影响相似，但水同位素序列通常较近期积雪杂质序列更易受季节效应的干扰而发生畸变。本研究通过主要离子与水同位素记录的点位间及点位内变异性，在十年至百年时间尺度上对上述发现进行了验证说明。点位内对比分析还探讨了低积累率钻探点位基岩上方数米处观测到的显著水同位素亏损现象。