Comparing and refining two novel methods for paleothermometry in speleothems - carbonate clumped isotopes vs. fluid inclusion noble gas concentrations

洞穴状方解石越来越多地被用作古气候档案。然而，它们的碳、氧同位素受许多参数的影响，因此不能用于直接恢复古温度。已开发出独立于方解石δ18O确定绝对古温度的创新方法。流体包裹体稀有气体浓度和碳酸盐簇状同位素测温是最有前景的两种方法。块状同位素温度计是基于碳酸盐晶格中13C-18O键随温度变化的丰度，已成功地应用于各种海洋生物的碳酸盐贝壳中，反映了方解石形成期间的温度。惰性气体方法是基于气体在水中随温度变化的溶解度，是地下水中传统惰性气体方法的变种，适用于洞穴相流体包裹体。这两种方法的精度都达到±1℃。这两种方法分别在以色列和德国的洞穴中进行了初步测试，虽然在现代系统中观察到了温度偏差，但在不同的时间段之间得到了合理的温差。这两种方法都受到不同限制的限制：在成团同位素情况下的非平衡分馏还没有被很好地理解，在惰性气体测温的情况下在一些石笋中检测到过剩成分。这项拟议的研究将通过测量现代洞穴沉积物样品和已经确定惰性气体温度的样品中的块状同位素来比较这两种测温方法。这将使我们能够更好地了解在这两种方法中观察到的温度偏差的来源，并表征这些方法可以应用的洞穴形成条件。

Speleothem calcite is increasingly used as paleoclimate archive. However, their carbon and oxygen isotopes are affected by many parameters and therefore cannot be used for direct paleotemperature reconstruction. Innovative methods have been developed to determine absolute paleotemperatures independently of calcite δ18O. Fluid inclusion noble gases concentrations and carbonate clumped isotope thermometry are two of the most promising approaches. The clumped isotope thermometer is based on the temperature dependent abundance of 13C-18O bonds in the carbonate lattice and has been successfully applied in carbonate shells from a variety of marine organisms, reflecting the temperature during calcite formation. The noble gas method is based on the temperature dependent solubility of gases in water and is a variant of the traditional noble gas approach in groundwater, applied to speleothem fluid inclusions. The precision of both methods is up to ± 1°C. Preliminary tests of these methods in speleothems from Israel and Germany, respectively, resulted in reasonable temperature differences between distinct time periods though in both methods a temperature offset in the modern system was observed. Both methods are limited by different constraints; the not-well understood non-equilibrium fractionation in the case of clumped isotopes and a surplus component detected in some stalagmites in the case of the noble gas thermometry. The proposed research will compare the two thermometry methods by measuring clumped isotopes in modern speleothem samples and in samples where noble gas temperatures have been already determined. This will enable us to better understand the source of temperature offsets observed in both methods and to characterize the speleothem formation conditions in which these methods can be applied.