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方法来了解蓝藻和真核藻类中与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不受成岩作用影响的地表水氮的重要新指标。沉积样品中叶绿素衍生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15N分级的较大分类群特定差异允许使用沉积氯化色素和总氮之间的15N偏移量来重建蓝藻和真核藻对出口生产的贡献。为了使用氯化色素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方法来计算沿着叶绿素生物合成途径的每一步的酶分馏，以确定重要的分馏发生在哪里。将测量纯化的叶绿素生物合成的代谢中间产物的同位素组成。代谢组学技术，如动态通量分析，将被用来测量中间池大小和途径分支点的通量。将整合同位素、浓度和通量数据，以便了解对所表达的分馏的控制。智力价值：更好地了解藻类和蓝藻叶绿素中15N组分的控制，将促进一种强大的新的古海洋学指标的使用。除了这项工作对理解海洋氮循环的明显贡献之外，这种方法还为理解保存在沉积记录中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处，因为它允许将产生沉积有机质的生物的分类特征信息与其新陈代谢或营养底物的信息联系起来。该方法可直接应用于其他生物标记物系统。这种方法的新颖性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，在生物地球化学研究中具有巨大的潜力。更广泛的影响：进一步开发一种具有不同用途的新的化合物特异性同位素替代物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非常重要。该项目将有助于改善STEM教育和增加妇女对科学的参与。拟议的工作包括对本科生实习生和一名女高中生进行培训和指导。在这一项目的配合下，调查员通过正在进行的海洋学小学课程设计工作参与了外联工作。这位调查员还积极参与努力，通过在她所在的部门建立一个妇女小组，并开发一系列讲座，将著名的女性地球科学家带到她所在的部门，进行为期数天的互动访问，重点是科学研究和指导，从而增加妇女在地球科学领域的留住。

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.