EAR-PF: Testing if the SPICE is right - disentangling diagenesis, seawater chemistry, and ecological change across Cambrian trilobite extinctions using Ca and Mg isotope ratios

Preston Cosslett Kemeny博士获得了美国国家科学基金会地球科学博士后奖学金，在Clara博士Blättler的指导下在芝加哥大学开展研究，专业发展和推广活动。在这个项目中，Kemeny博士将研究寒武纪（约5.4亿至4.85亿年前）三叶虫灭绝与海水化学之间的关系。这项工作对未来几十年建立健全的环境和生态政策具有广泛的意义，因为了解古代生命和气候的交织性质为预测和应对人为气候变化提供了基础背景。以前，对岩石化学变化的许多解释暗示了全球碳循环与生态循环之间的因果关系。然而，沉积过程研究的最新进展表明，灭绝和多样化与环境扰动的关系可能很弱。寒武纪为测试生态学和海水化学之间的联系提供了独特的机会，因为它包含了与化学异常相关的多个三叶虫灭绝和多样化间隔。在这项工作中，Kemeny博士将对寒武纪岩石和化石进行地球化学测量，并在数值模型中综合这些观察结果，以更好地了解灭绝与全球碳循环之间的关系。此外，Kemeny博士将继续努力通过研究、教学、指导和服务活动来创建一个包容性的社区，以增加地球科学的多样性、公平性、包容性和可及性。这些活动将包括指导本科生和研究生，培训有效和包容的教学法，并与当地教师合作制定有关全球碳循环和古生物学的公开课程计划。该项目将通过量化全球碳循环与寒武纪三叶虫灭绝之间的联系，研究生命与气候的共同进化。Kemeny博士将(1)测量密苏里盆地岩心样品中的钙和镁同位素比率，以确定寒武纪阶阶正碳同位素偏移（SPICE）是否反映了海洋13C/12C比率的变化或沉积后蚀变或矿物学的变化，(2)使用硫和铀同位素比率测试SPICE事件期间海洋缺氧的现有假设。(3)评价三叶虫化石作为成岩改造和海水化学的新代用物；(4)在海洋-大气系统的箱形模型中再现同位素观测，并在数值上约束成岩作用产生碳同位素漂移的时空尺度。通过在SPICE活动期间将生物多样性变化与环境变化分开，该项目将采取具体步骤来理解生命与气候的共同进化。此外，通过探索基于三叶虫的成岩蚀变代理，本研究可为地球化学界重建海洋化学和研究古生代全球碳循环与生态转换之间的联系提供新的工具。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。

Dr. Preston Cosslett Kemeny has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out research, professional development, and outreach activities at the University of Chicago under the mentorship of Dr. Clara Blättler. In this project, Dr. Kemeny will investigate the relationship between trilobite extinction and seawater chemistry during the Cambrian Period (approximately 540 to 485 million years ago). This work has broad implications for establishing robust environmental and ecological policy in the coming decades because understanding the interwoven nature of ancient life and climate provides fundamental context for predicting and responding to anthropogenic climate change. Previously, many interpretations of chemical variability in rocks implicated causal linkages between the global carbon cycle and ecological turnover. However, recent developments in the study of sedimentary processes have suggested that extinction and diversification may only weakly relate to environmental perturbations. The Cambrian Period offers unique opportunities for testing connections between ecology and seawater chemistry because it contains multiple trilobite extinction and diversification intervals associated with chemical anomalies. In this work, Dr. Kemeny will perform geochemical measurements on Cambrian rocks and fossils, and synthesize those observations within a numerical model, to better understand the relationship between extinction and the global carbon cycle. In addition, Dr. Kemeny will continue efforts to create an inclusive community through research, teaching, mentorship, and service activities that increase diversity, equity, inclusivity, and accessibility in the geosciences. These activities will include mentoring undergraduate and graduate students, training in effective and inclusive pedagogy, and working with local teachers to develop publicly available lesson plans on the global carbon cycle and paleontology.This project will study the coevolution of life with climate by quantifying connections between the global carbon cycle and trilobite extinction during the Cambrian Period. Dr. Kemeny will (1) measure calcium and magnesium isotope ratios in drill core samples from the Missouri basin to determine whether the Cambrian Steptoean Positive Carbon Isotope Excursion (SPICE) reflects a shift in the marine 13C/12C ratio or a shift in either the style of post-depositional alteration or mineralogy, (2) test existing hypotheses of marine anoxia during the SPICE event using sulfur and uranium isotope ratios, (3) evaluate trilobite fossils as a novel proxy for diagenetic modification and seawater chemistry, and (4) reproduce the isotopic observations within a box model of the ocean-atmosphere system and numerically constrain the temporal and spatial scales over which diagenesis can produce carbon isotope excursions. By disentangling biodiversity change from environmental change during the SPICE event, this project will take concrete steps towards understanding the coevolution of life with climate. Furthermore, by exploring a trilobite-based proxy for diagenetic alteration, the proposed work may provide a new tool to the geochemical community for reconstructing marine chemistry and for studying connections between the global carbon cycle and ecological turnover throughout the Paleozoic.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.