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

海洋的化学演化从根本上与整个地球历史上的气候变化和生物进化有关。直接重建海水过去的离子组成的方法很少，因此对海水镁钙比(mg/Ca)的经验约束非常有限。我们建议通过结合使用新的碳酸盐“块状同位素”温度计重建的温度和海底有孔虫的镁/钙比值来发展白垩纪至更新世海水镁/钙比值的记录。这一海水镁/钙的记录将被用来检验几个假设：1)我们将测试海洋的镁/钙比和[钙]是否像一些作者所说的那样比以前认为的更加动态。我们将首次能够准确地确定海水中镁/钙的变化时间和大小，这是碳循环模型和基于镁/钙的古温度重建所需的数据。2)我们将测试海洋生物矿化进化变化的主要驱动力是否是海水中镁/钙的长期变化。我们将把我们的海水镁/钙记录与随着时间推移的主要造礁和沉积物生产者的骨骼矿物学进行比较。

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.