OCE-RIG: The chlorophyll 15N proxy for nitrogen cycling and export production: Understanding nitrogen isotope fractionations in chlorophyll biosynthesis

概述：在这个项目中，研究人员将使用多学科的方法来了解与蓝藻和真核藻类叶绿素生物合成相关的氮同位素分馏。叶绿素降解产物的氮同位素比值是一个重要的新的地表水氮，是不改变成岩作用的代理。来自沉积物样本中叶绿素的生物标志物可以保存数亿年，因此可以作为了解古代海洋氮循环的工具。此外，叶绿素15 N分馏的大类群特异性差异允许使用沉积的chloropigment和散装氮之间的15 N补偿重建蓝藻和真核藻类的出口生产的贡献。为了使用氯色素15N代用品，必须了解同位素分馏的这些差异。这项工作使用同位素盒模型的方法来计算酶分馏在每一步沿着叶绿素生物合成途径，以确定重要的分馏发生。将测量叶绿素生物合成的纯化代谢中间体的同位素组成。代谢组学技术，如动力学通量分析，将用于测量中间池的大小和沿着途径分支点的通量。同位素，浓度和通量数据将被整合，以了解表达分馏的控制。智力优势：更好地了解藻类和蓝藻叶绿素中15 N分馏的控制将提高一个强大的新的古海洋学代理的使用。除了这项工作对理解海洋氮循环的明显贡献之外，这种方法还为理解沉积记录中保存的有机分子的分馏提供了一个新的框架。这些分子化石的同位素分析在古海洋学中有很大的用途，因为它可以将产生沉积有机质的生物的分类身份的信息与其代谢或营养基质的信息联系起来。所提出的方法可以直接应用于其他生物标志物系统。这种方法的新奇在于它结合了稳定同位素地球化学和代谢组学的分析技术，代谢组学是生物医学研究中的一个新兴领域，在地球化学研究中具有巨大的潜力。更广泛的影响：进一步开发具有不同应用的重要的新化合物特定同位素代用品将有助于我们了解现代海洋氮循环，这对于预测和减轻人为气候变化对海洋生物地球化学的影响至关重要。该项目将有助于改善STEM教育和增加妇女对科学的参与。拟议的工作包括培训和指导本科实习生和一名女高中生。结合这一项目，调查员通过正在进行的海洋学基础小学课程设计工作参与外联活动。调查员还积极参与努力，以增加保留妇女在地球科学，建立一个小组，为妇女在她的部门，并制定了讲座系列，使突出的女地球科学家到她的部门进行为期多日的互动访问，将重点放在科学研究和指导。

Overview: In this project, the investigator will use a multidisciplinary approach to understand nitrogen isotope fractionations associated with chlorophyll biosynthesis in cyanobacteria and eukaryotic algae. Nitrogen isotope ratios of chlorophyll degradation products are an important new proxy for surface water nitrogen that is unaltered by diagenesis. Biomarkers derived from chlorophyll in sedimentary samples can be well preserved for hundreds of millions of years, and can therefore act as a tool for understanding ancient marine nitrogen cycling. Additionally, large taxon-specific differences in chlorophyll 15N fractionations allow for the use of 15N offsets between sedimentary chloropigment and bulk nitrogen to reconstruct the contribution of cyanobacteria and eukaryotic algae to export production. In order to use the chloropigment 15N proxy, these differences in isotopic fractionation must be understood. The work uses an isotope box model approach for calculating enzymatic fractionations at each step along the chlorophyll biosynthetic pathway in order to determine where important fractionations occur. Purified metabolic intermediates of chlorophyll biosynthesis will be measured for their isotopic composition. Metabolomics techniques such as kinetic flux profiling will be used to measure intermediate pool sizes and fluxes along pathway branch points. Isotope, concentration, and flux data will be integrated in order to understand the control of expressed fractionations. Intellectual Merit: A better understanding of the controls of 15N fractionations in algal and cyanobacterial chlorophyll will improve the use of a powerful new paleoceanographic proxy. Beyond the obvious contributions of this work to understanding marine nitrogen cycling, this approach provides a new framework for understanding fractionations of organic molecules that are preserved in the sedimentary record. Isotopic analysis of these molecular fossils has great utility in paleoceanography because it allows for linking of information on taxonomic identity of organisms that produce sedimentary organic matter with information about their metabolism or nutrient substrates. The proposed approach can be directly applied to other biomarker systems. The novelty in this approach lies in its combination of analytical techniques from stable isotope geochemistry and metabolomics, an emerging field in biomedical research that has tremendous potential in biogeochemical studies. Broader Impacts: Further development of an important new compound-specific isotope proxy with diverse applications will contribute to our understanding of the modern marine nitrogen cycle, which is important for predicting and mitigating the effects of anthropogenic climate change on marine biogeochemistry. This project will contribute to improving STEM education and increasing the participation of women in science. The proposed work involves training and mentoring of undergraduate interns and a female high school student. In conjunction with this project, the investigator is involved in outreach through ongoing work on oceanography-based elementary school curriculum design. The investigator is also actively involved in efforts to increase retention of women in geosciences by establishing a group for women in her department, and developing a lectureship series to bring prominent female geoscientists to her department for multi-day interactive visits that will focus on both scientific research and mentoring.