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

古气候数据为预测未来气候变化的模型提供了校准的背景。在这种情况下，年代准确、分辨率高的洞穴沉积是有益的，但洞穴和洞穴受到一系列复杂过程的影响，这些过程发生在大气、土壤地带、岩溶地带或洞穴本身。在世界各地的洞穴中执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(镁)同位素系统有助于理解土壤和岩溶地带发生的过程。这是因为镁同位素比值提供了关于岩石-水相互作用、水停留时间和风化过程的信息。然而，到目前为止，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，到目前为止，白云岩(富镁碳酸盐)洞穴几乎完全没有人看管。在这里，我建议分析白云岩洞穴中采集的滴水和洞穴(方解石和文石)的镁同位素组成。由于过去几年实施的监测方案，波鸿鲁尔大学已经提供了拟议项目所需的所有样本材料。样本来自德国和摩洛哥的洞穴，因此，不同的气候环境。首先将分析土壤(含镁硅酸盐)、寄主岩石(白云岩/石灰岩)和洞穴物质中的镁含量。随后，将分析所有样本，包括由于监测方案而已知镁浓度的滴水，以确定其镁同位素组成。这项建议的目的包括：(I)记录白云岩洞穴滴水的镁同位素变异性，作为硅酸盐和碳酸盐风化比变化的函数，从而记录温度和降雨量的变化；(Ii)评估影响不同气候带硅酸盐和碳酸盐风化比的主导因素(温度或降雨量)；(Iii)鉴定文石和方解石石笋中的镁同位素变异性，作为硅酸盐和碳酸盐风化比的变化，从而温度和降雨量的变化以及(Iv)测试先前方解石降水(PCP)对镁同位素组成的影响。这些目的导致了以下工作假说的验证：在白云岩洞穴的情况下，镁同位素系统足以替代过去的气候重建和PCP过程。拟议的项目将不仅在白云岩洞穴中，而且在一般情况下，从而在古气候研究中促进对镁同位素系统的更高水平的了解。

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.