Magnesium isotope time-series analyses of dolostone cave dripwater and speleothems: Proxy calibration and application

古气候数据为校准预测未来气候变化的模型提供了背景。在这方面，年代久远、高分辨率的洞穴沉积物是有用的，但洞穴和洞穴沉积物受到一系列复杂过程的影响，这些过程发生在大气、土壤区、岩溶区或洞穴本身。在世界各地的洞穴中进行的监测方案揭示了这些过程。最近的研究表明，非传统的镁（Mg）同位素系统是了解发生在土壤和岩溶带的过程。这是因为镁同位素比值提供了岩石-水相互作用，水的停留时间和风化过程的信息。然而，迄今为止，研究主要集中在石灰岩（贫镁碳酸盐）洞穴中形成的洞穴。另一方面，白云岩（富镁碳酸盐）洞穴几乎完全被忽视到目前为止，在这里，我建议分析的滴水沃茨和洞穴沉积物（方解石和文石）的Mg同位素组成的白云岩洞穴。由于过去几年执行的监测计划，拟议项目所需的所有样本材料都已在波鸿鲁尔大学提供。样品来自德国和摩洛哥的洞穴，因此，不同的气候环境。首先分析土壤（含镁硅酸盐）、寄主岩石（白云岩/石灰岩）和洞穴沉积物材料的镁浓度。随后，将对所有样本，包括监测方案中已知镁浓度的滴水沃茨，进行镁同位素组成分析。所获得的数据将与附近气象站的温度和降雨量数据相结合，以解释镁同位素变异性。本提案的目标包括：（i）记录白云岩洞穴滴水沃茨的镁同位素变异性，作为硅酸盐与碳酸盐风化比变化的函数，从而，温度和降雨量的变化，（二）对主导因素的评价（iii）文石和方解石石笋中Mg同位素的变异性作为硅酸盐与碳酸盐风化比的变化，因此，温度和降雨量的变化和（iv）测试之前的方解石沉淀（PCP）对Mg同位素组成的影响。这些目标导致以下工作假设的验证：在白云岩洞穴的情况下，镁同位素系统是一个足够的代理过去的气候重建和过程PCP。该项目将导致镁同位素系统的先进水平的理解不仅在白云岩洞穴，而且在一般情况下，因此，在古气候研究。

Palaeoclimate data provide the background against which models, forecasting future climate changes, are calibrated. Well-dated, high-resolution speleothem deposits are instrumental in this context, but caves and thus speleothems are affected by a complex spectrum of processes, which take place in the atmosphere, the soil zone, the karst zone or the cave itself. Monitoring programmes performed in caves worldwide shed light on these processes. Recent studies have shown that the non-traditional Magnesium (Mg) isotope system is instrumental in understanding processes taking place in the soil and karst zone. This is because Mg isotope ratios provide information on rock-water interaction, water residence time and weathering processes. However, research focused mainly on caves formed in limestone (Mg-poor carbonate) caves up to now. On the other hand, dolostone (Mg-rich carbonate) caves were nearly completely unattended so far.Here, I propose to analyse the Mg isotopic composition of drip waters and speleothems (calcite and aragonite) collected in dolostone caves. All sample material needed for the proposed project is already available at the Ruhr-University Bochum due to monitoring programmes performed in the past few years. Samples are from German as well as Moroccan caves and thus, different climate settings. Soil (Mg-bearing silicates), host rock (dolostone/limestone) and speleothem material will first be analysed regarding the Mg concentration. Subsequently all samples, including drip waters with known Mg concentration due to the monitoring programmes, will be analysed for their Mg isotope composition. The obtained data will be set in context with temperature and rainfall amount data of nearby meteorological stations in order to interpret the Mg isotope variability.The objectives of this proposal include (i) the documentation of the Mg isotope variability of dolostone cave drip waters as a function of changes in the silicate versus carbonate weathering ratio and thus, changes in temperature and rainfall amount, (ii) the evaluation of a dominant factor (temperature or rainfall amount) influencing the silicate versus carbonate weathering ratio in different climate belts, (iii) the identification of the Mg isotope variability in aragonite and calcite stalagmites as changes in the silicate versus carbonate weathering ratio and thus, changes in temperature and rainfall amount and (iv) testing the influence of prior calcite precipitation (PCP) on the Mg isotope composition. These aims lead to the verification of the following working hypothesis: In case of dolostone caves, the Mg isotopes system is an adequate proxy for past climate reconstructions and the process PCP. The proposed project will lead to an advanced level of understanding of the Mg isotope system not only in dolostone caves but also in general and thus, in palaeoclimate research.