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

白云岩洞穴滴水和洞穴的镁同位素时间序列分析：代理校准和应用

• 批准号: 374585249
• 负责人: Dr. Sylvia Riechelmann
• 金额: --
• 依托单位: Institut für Geologie, Mineralogie und Geophysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/374585249?language=en
• 关键词: Magnesium; isotope; time; series; analyses

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.

古气候数据提供了校准预测未来气候变化模型的背景。年代明确的高分辨率洞穴沉积物在这方面发挥了重要作用，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、土壤区域、喀斯特区域或洞穴本身。在世界各地的洞穴中进行的监测项目揭示了这些过程。最近的研究表明，非传统镁 (Mg) 同位素系统有助于了解土壤和喀斯特地区发生的过程。这是因为镁同位素比提供了有关岩石-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，白云岩（富含镁的碳酸盐）洞穴迄今为止几乎完全无人看管。在这里，我建议分析白云岩洞穴中收集的滴水和洞穴沉积物（方解石和霰石）的镁同位素组成。由于过去几年开展的监测项目，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，因此气候环境不同。首先将分析土壤（含镁硅酸盐）、主岩（白云岩/石灰岩）和洞穴材料的镁浓度。随后，将对所有样品（包括由于监测计划而具有已知镁浓度的滴水）进行镁同位素组成分析。获得的数据将与附近气象站的温度和降雨量数据结合起来，以便解释镁同位素变异性。本提案的目标包括 (i) 将白云岩洞穴滴水的镁同位素变异性记录为硅酸盐与碳酸盐风化比变化以及温度和降雨量变化的函数，(ii) 影响不同气候带硅酸盐与碳酸盐风化比的主导因素（温度或降雨量）的评估，(iii)身份证明文石和方解石石笋中镁同位素变异性随着硅酸盐与碳酸盐风化比的变化以及温度和降雨量的变化而变化，以及（iv）测试先前方解石沉淀（PCP）对镁同位素组成的影响。这些目标验证了以下工作假设：对于白云岩洞穴，镁同位素系统可以充分代表过去的气候重建和 PCP 过程。拟议的项目不仅将提高对白云岩洞穴中的镁同位素系统的了解，而且还将提高对整个古气候研究的镁同位素系统的了解。