NSFOCE-BSF: Foraminiferal Na/Ca: a new proxy for reconstructing Cenozoic seawater composition

海水成分的变化对地球气候和海洋中的生物过程具有重要影响，因为它们与碳循环有关。具体而言，新生代（过去约6500万年）海洋中钙浓度的历史与陆地上硅酸盐和碳酸盐岩石的化学风化以及海洋中碳酸盐矿物的沉淀和溶解密切相关，这些过程控制着大气二氧化碳浓度的长期变化，从而强烈影响全球气候。 鉴于目前由于温室气体的增加而加速了地球化学循环，这些过去的过程可能会为未来没有现代类似物的条件提供见解。这项研究旨在开发一种新的方法，通过与海水钠浓度的比较来重建海洋中钙的变化，海水钠浓度被认为在数千万年的时间尺度上是恒定的。该项目是通过一个特殊的机会资助美国-以色列海洋科学合作。该项目将培训一名美国博士后和两名以色列研究生，他们将在两个实验室工作，并与两位主要研究人员互动。该项目还涉及几名本科生，他们将接受各种实验室活动的培训。本研究为利用有孔虫Na/Ca值重建新生代海水钙浓度（[Ca]）提供了一种新的方法。将进行培养实验（由以色列团队领导）和岩心顶部校准（由美国团队领导），以进一步验证初步观察结果，并生成底栖有孔虫中Na/Ca和其他元素比率的记录，作为重建新生代海水化学的手段。对底栖动物（盖盖螺（Operculinaammonoides））、氨螺（Ammonitepida）和裂叶双盖螺（Amphisteginalobifera）和浮游动物（G. ruber和G. siphnifera）有孔虫的分布系数将被用来确定Na/Ca和上述其他元素在不同海水[Ca]和在可变和恒定方解石饱和度条件下的分配系数。 这些实验和岩心顶部校准的结果将用于生成过去5500万年的完整Na/Ca记录。

Variations in the composition of seawater have important implications for Earth climate and biological processes in the ocean because of their relation to the carbon cycle. Specifically, the history of calcium concentration in the ocean over the Cenozoic (past ~65 million years) is tightly linked to chemical weathering of silicate and carbonate rocks on land and the precipitation and dissolution of carbonate minerals in the ocean, processes that control long-term changes in atmospheric carbon dioxide concentration and thus strongly influence global climate. Given the current acceleration of biogeochemical cycling due to the increase in greenhouse gases, these past processes may provide insights to future conditions that have no modern analogs. This research seeks to develop a new method of reconstructing variability in calcium in the oceans using comparison to seawater sodium concentrations, which are thought to be constant on timescales of many tens of millions of years. The project is funded through a special opportunity for U.S.-Israeli collaboration in ocean sciences. The project will train a U.S. post-doc and two Israeli graduate students who will spend time at both labs and will interact with the two principal investigators. The project also involves several undergraduate students who will be trained in various laboratory activities. Specifically, this research will provide a new method to reconstruct Cenozoic seawater calcium concentrations ([Ca]) using foraminiferal Na/Ca. Culture experiments (led by the Israeli team) and core top calibrations (led by the U.S. team) will be undertaken to further validate preliminary observations and generate records of Na/Ca and other elemental ratios in benthic foraminifera as means for reconstructing Cenozoic seawater chemistry. Culture experiments of benthic (Operculina ammonoides, Ammonia tepida and Amphistegina lobifera) and planktonic (G. ruber and G. siphnifera) foraminifera will be used to determine the distribution coefficients of Na/Ca and the other elements discussed above at different seawater [Ca] and under variable and constant calcite saturation conditions. The results from these experiments and core top calibrations will be used to generate a complete Na/Ca record for the last 55 Myr.