Collaborative Research: Deep ocean temperature and continental ice volume from benthic foraminiferal test composition, 77Ma to Present

海底沉积物记录了地球气候系统的自然变化。研究沉积物记录可以提高我们预测气候系统如何对人类活动做出反应的能力。这个项目将产生深海温度、大陆冰量和大气二氧化碳的记录。这些记录将记录过去7700万年气候系统的变化。这些数据将提高我们对极地放大等过程的理解，以及地球系统适应不同大气二氧化碳浓度的能力。这项研究还将提高我们对深海温度和冰盖体积变化的长期变化及其与大气二氧化碳变化的联系的认识。该项目将由两名女科学家执行，其中一人是一名早期职业研究员。几名本科生和研究生将参与拟议的研究活动。外展计划将包括来自初中和高中的地球/环境科学教师。底栖有孔虫是过去环境条件的优秀记录者。特别是，底栖有孔虫（bf）镁/钙比（Mg/Ca）被用作温度代理，从而可以将温度与冰体积对广泛使用的bf氧同位素代理（d18O）的影响分离开来。然而，bf Mg/Ca信号是复杂的依赖于碳酸盐饱和状态（“ω”）除了温度。底栖有孔虫锂、硼和锶与钙的比值（Li-B-Sr/Ca）有望分离温度和ω对bf Mg/Ca的贡献。拟开展的研究包括：1)利用bf d18O结合bf Mg-Li-B-Sr/Ca，构建白垩纪晚期和新生代（~77 ~ 0 Ma）的温度和冰体积史；2)在古深度样带中校准多种物种的bf Mg-Li-B-Sr/Ca偏移量，以涵盖ω范围。不同物种对温度、欧米茄和海水元素/钙比变化的生理反应将使用多变量模型来解决。1 - myr的样品间距将用于校准，而新的更高分辨率（~200 Kyr）记录将提供自77 Ma以来bf Mg/Ca变化的稳健数据集。该数据集将与bf - d18O数据一起用于验证深海温度和大陆冰量从晚白垩世到新生代共变的假设。深海温度（和化学）、大陆冰量和大气二氧化碳浓度的变化之间的联系将使用海洋碳循环的数值盒模型进行研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Sea floor sediments record the natural variability of the Earth’s climate system. Studying sediment records can improve our ability to predict how the climate system will respond to human activities. This project will produce records of deep-sea temperatures, continental ice volume, and atmospheric carbon dioxide. The records will document changes in the climate system over the last 77 million years. Those data will improve our understanding of processes such as polar amplification and the ability of the Earth’s system to adjust to different atmospheric carbon dioxide concentrations. This study will also improve our knowledge of long-term changes in deep ocean temperatures and ice-sheet volume variability and their connection to changes in atmospheric carbon dioxide. The project will be carried out by two female scientists, one of whom is an early career researcher. Several undergraduate and graduate students will participate to the proposed research activities. The outreach program will involve Earth/Environmental Science teachers from middle and high schools. Benthic foraminifera are excellent recorders of past environmental conditions. In particular, the benthic foraminiferal (bf) magnesium/calcium ratio (Mg/Ca) is used as a temperature proxy, making it possible to separate temperature from ice volume effects on the widely used bf oxygen isotope proxy (d18O). However, the bf Mg/Ca signal is complicated by a dependency on carbonate saturation state (“omega”) in addition to temperature. Benthic foraminiferal lithium, boron and strontium to calcium ratios (Li-B-Sr/Ca) show promise in separating the temperature and omega contributions to bf Mg/Ca. The proposed research will: 1) construct robust temperature and ice volume histories during the late Cretaceous and Cenozoic (~77-0 Ma) using bf d18O in conjunction with bf Mg-Li-B-Sr/Ca; and 2) calibrate offsets in bf Mg-Li-B-Sr/Ca for multiple species across paleodepth transects to encompass a range of omega. Different species’ physiological response to variations in temperature, omega, and seawater element/Ca ratios will be addressed using a multivariate model. One-Myr sample spacing will be used for the calibrations, whereas a new higher-resolution (~200 Kyr) record will provide a robust dataset of bf Mg/Ca variations since 77 Ma. This dataset will be used, together with bf d18O data, to test the hypothesis that deep ocean temperature and continental ice volume covary from the Late Cretaceous to the Cenozoic. The connections among changes in deep ocean temperature (and chemistry), continental ice volume, and atmospheric carbon dioxide concentration will be investigated using a numerical box model of the ocean carbon cycle.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.