Evolution of seawater Mg/Ca ratios since the Cretaceous: New constraints from the carbonate 'clumped isotope' thermometer.

海洋的化学演变与整个地球历史上的气候变化和生物演变有着根本的联系。很少有方法存在直接重建过去的海水离子组成，因此，海水镁钙比（Mg/Ca）的经验约束是非常有限的。我们建议开发一个记录的海水Mg/Ca的白垩纪更新世相结合的温度重建使用新的碳酸盐“聚集同位素”温度计与底栖有孔虫Mg/Ca比的测量。海水Mg/Ca的这一记录将用于检验几个假设：1）我们将检验海洋的Mg/Ca比和[Ca 2 +]是否比以前认为的更具动态性，正如一些作者所建议的那样。我们将首次能够精确地确定海水Mg/Ca变化的时间和幅度，这是碳循环模型和基于Mg/Ca的古温度重建所需的数据。2)我们将测试是否在海洋生物的生物矿化的进化变化的主要驱动力是长期变化的海水镁/钙。我们将比较我们的记录海水镁/钙的骨骼矿物学占主导地位的造礁者和沉积物生产者通过时间。

The chemical evolution of the oceans is fundamentally tied to climate change and biological evolution throughout Earth history. Few methods exist for directly reconstructing the past ionic composition of seawater, and thus empirical constraints on seawater magnesium to calcium ratios (Mg/Ca) are very limited. We propose to develop a record of seawater Mg/Ca for the Cretaceous to Pleistocene by combining temperatures reconstructed using the new carbonate 'clumped isotope' thermometer with measurements of benthic foraminiferal Mg/Ca ratios. This record of seawater Mg/Ca will be used to test several hypotheses: 1) We will test whether the Mg/Ca ratio and [Ca2+] of the oceans were much more dynamic than previously thought, as some authors have suggested. We will for the first time be able to precisely determine the timing and magnitude of changes in seawater Mg/Ca, data which are required for both carbon cycle models and Mg/Ca-based paleotemperature reconstructions. 2) We will test whether a major driving force for evolutionary change in biomineralization of marine organisms was secular variation in seawater Mg/Ca. We will compare our record of seawater Mg/Ca with the skeletal mineralogy of dominant reef-builders and sediment producers through time.