Influences of high reliefs on isotope hydrology and coupled climate proxies

气候代用物，如树木年轮，依靠稳定的同位素比率来重建古气候条件。这些信息可以用来校准评估和预测全球气候变化正在发生和未来影响的模式。根据模型预测，地中海西部地区将面临严重的气候变化。因此，该地区的科西嘉岛一直是通过树木年代学和稳定同位素重建古气候的目标。然而，科西嘉松树的氧稳定同位素结果还不能令人满意地解释。树木年轮的氧稳定同位素值（delta18O）主要取决于当地降水和土壤水分的氧同位素比值。降水delta18O值随温度、海拔和湿源地区的不同而变化。这些参数现在是相当精确的，但过去需要假设。一个重要的同位素效应是所谓的海拔效应，它描述了降水delta18O值与海拔的关系。国际原子能机构（IAEA）的大型全球降水同位素网络（GNIP）数据库允许对同位素效应进行良好的区域估计。然而，在高山陡峭的地区，事情变得更加困难。一些最新的出版物表明，在特定的季节，这些地区没有高度梯度。观测结果的原因可能是大气行星边界层（PBL）的季节性高度变化。这个同位素水文学提案是CorsicArchive项目包的一部分，该项目包还包括气候、树木同位素和树木生态学的相互关联的提案。计划沿东西高度样带安装并定期取样9个同位素降水采样器。本提案将专门探讨PBL的动力学和同位素高度效应。其他问题涉及气团的水分来源和岛屿水文循环内的当地水分再循环。此外，土壤水和地表水分析计划追踪和量化沿水到树木年轮路径的delta18O值的变化。本文提出的方法旨在填补目前高海拔地区同位素水文知识的空白，并最终导致对气候变化敏感地区相关气候指标的更可靠解释。就目前的气候变化而言，了解过去的气候变化及其触发因素对于更好地预测未来的变化至关重要。

Climate proxies such as tree rings rely on stable isotope ratios for the reconstruction of palaeoclimatic conditions. Such information then allow the calibration of models that evaluate and predict ongoing and future effects of global climate change. According to model predictions, the western Mediterranean is a region that will face severe climatic changes. Therefore, the island of Corsica in that region has been the target for palaeoclimate reconstructions by means of dendrochronology and stable isotopes. However, the oxygen stable isotope results from Corsican pines could not yet be interpreted satisfactorily. The oxygen stable isotope values (delta18O) of tree rings mainly depend on the oxygen isotope ratio of local precipitation and soil water. The precipitation delta18O values vary according to temperature, altitude and the moisture source area. Such parameters are determined nowadays rather precise but need to be assumed for the past. An important isotope effect is the so-called altitude effect that describes the relation of the delta18O value of precipitation and altitude. The large global network of isotopes in precipitation (GNIP) database of the International Atomic Energy Agency (IAEA) allows for a good regional estimate of isotope effects. However, things become more difficult in regions with high and steep mountain reliefs. Some latest publications suggest that the altitude gradient is absent in such regions during specific seasons. The reason for that observation could be seasonal height variations of the atmospheric planetary boundary layer (PBL). This isotope hydrology proposal is part of the project package CorsicArchive that also consists of interlinking proposals for climate, dendroisotopes and dendroecology. It is planned to install and regularly sample nine isotope precipitation samplers along an east-west altitudinal transect. This proposal will specifically explore the dynamics of the PBL and the isotope altitude effect. Additional questions relate to moisture source of air masses and the local moisture recycling within the islands hydrologic cycle. Furthermore, soil water and surface water analyses are planned to trace and quantify changes of the delta18O values along the pathway of water to the tree rings. The approach of this proposal aims to fill the gaps in the current knowledge of isotope hydrology of high reliefs and will finally lead to a more robust interpretation of related climate proxies in a climate change sensitive region. With respect to the current climate change, it is essential to understand climatic variations and its triggers in the past to better predict future changes.