A tandem Mg/Ca-clumped isotope approach for palaeotemperature estimation of past climate

对全球温度变化幅度的估计是预测未来气候的核心。然而，大多数数值气候模拟研究都集中在仪器周期，这只涵盖了相对较短的时间（<100年）。为了更好地了解未来的气候变化，并测试这些模型的鲁棒性，重要的是重建整个地球历史上过去的温度变化。然而，这不是一个微不足道的问题，因为我们必须依赖于温度变化的代理人，而这些代理人往往会产生模糊的结果。在过去的几十年中，已经开发了几个过去海洋温度的替代物，包括古生态转换函数，Mg/Ca和生物标志物（UK'37，TEX 86）。在古温度测量的最新进展中，基于碳酸盐中13 C-18 O键丰度的“聚集同位素”的应用是其中之一。这种方法的优点是13 C18 O 16 O2的形成是温度依赖性的，但与溶解的无机碳和海水的d18 O无关。因此，同时测量“成团同位素”和传统的氧同位素提供了一个独特的解决方案，碳酸盐岩古温度方程约束温度和d18 O的水。有孔虫方解石的Mg/Ca比也同样显示出温度依赖性。因此，配对测量镁/钙和氧同位素从相同的有孔虫标本允许重建的氧同位素的海水。该提案的主要目的是将联合收割机的镁/钙测量和同一有孔虫试验的成块同位素测量结合起来，以产生独立的温度估计值。结合Mg/Ca和团聚体同位素古温度方程，可以预测Mg/Ca和团聚体同位素之间的预期关系。坚持化石有孔虫的预期关系将提供古温度估计的信心，或者，如果他们偏离预期的关系，将确定一个或两个代理的问题。最初，我们将使用现代有孔虫来测试预测的关系，这些有孔虫覆盖的温度范围约为100 ℃。6 ~ 28度进行验证和校准。接下来，我们将测试的方法在末次冰期的应用，在北大西洋的一个横断面的日期明确的沉积物芯。科学界对末次冰消期气候突变事件的严重程度仍有争议。例如，在这些极端事件期间，从海洋（~2-4度）和陆地（~6-10度）档案推断的热带冷却估计存在很大差异。这种差异可能是温度代理的季节性偏差的结果。然而，温度范围远远大于热带地区平均季节温差的预期。这就提出了一个问题，即这些差异是真实的，还是由特定代理的敏感性或可靠性差异造成的。通过对Mg/Ca和聚集同位素的串联测量，将有可能确定末次冰期气候突变事件期间温度变化的幅度并估计其空间范围。此外，第四纪晚期的井芯提供了一个理想的测试案例，我们的串联镁/钙聚集同位素古温度计的成功开发和应用将允许调查有关地球的气候历史的许多相关的开放性问题。

The estimation of the magnitude of global temperature change is central for predicting future climate. However, most numerical climate modeling studies have focused on the instrumental period, which covers only a relatively small amount of time (<100 years). To better understand future climate change and to test the robustness of these models, it is important to reconstruct past temperature changes throughout Earth history. This is not a trivial problem, however, because we must rely on proxies of temperature change that often yield ambiguous results. Over the past decades several proxies of past ocean temperature have been developed including palaeoecological transfer functions, Mg/Ca, and biomarkers (Uk'37, TEX86). Among the newest advances in palaeothermometry is the application of "clumped isotopes" which is based on the abundance of 13C-18O bounds in carbonates. The advantage of this method is that the formation of 13C18O16O2 is temperature dependent but independent of the dissolved inorganic carbon and the d18O of seawater. Therefore, the simultaneous measurement of "clumped isotopes" and traditional oxygen isotopes provides a unique solution to the carbonate palaeotemperature equation by constraining both temperature and d18O of water. The Mg/Ca ratio of foraminiferal calcite has been similarly shown to be temperature dependent. Hence, paired measurements of Mg/Ca and oxygen isotopes from the same foraminiferal specimens permit reconstruction of the oxygen isotopes of the sea water. The main aim of the proposal is to combine Mg/Ca and clumped isotope measurements of the same foraminiferal tests to produce independent estimates of temperature. By combining the Mg/Ca and clumped isotopes palaeotemperature equations, the expected relationship between Mg/Ca and clumped isotopes can be predicted. Adherence to the expected relationship in fossil foraminifera will provide confidence in the palaeotemperature estimates or, if they diverge from the expected relationship, will identify problems with either one or both proxies. Initially, we will test the predicted relationship using modern foraminifera which cover a temperature range from approx. 6 to 28 degree to verify and calibrate the method. Next, we will test the application of the method during the last glacial period using a transect of well-dated sediment cores in the north Atlantic. The magnitude of abrupt climate change events during the last deglacial is still under debate in the scientific community. For example, large discrepancies exist in estimates of tropical cooling inferred from marine (~2-4 degree) and terrestrial (~6-10 degree) archives during these extreme events. This discrepancy may be the result of seasonal bias of the temperature proxies. However, the temperature range is much larger than expected for average seasonal temperature differences in the tropics. This raises the question whether these discrepancies are real or caused by differences in the sensitivity or reliability of specific proxies. With tandem measurements of Mg/Ca and clumped isotopes it will be possible to determine the magnitude of temperature change and estimate its spatial extent during abrupt climate change events of the last glacial. Furthermore, the well-dated cores of the late quaternary provide an ideal test case for our tandem Mg/Ca-clumped isotope palaeothermometer whose successful development and application will permit to investigate many relevant open questions about earth's climate history.