Collaborative Research: The Roles of Seasonality, Silicification, and Alteration in Nitrogen and Silicon Isotope Paleo-proxy Variability

硅藻化石（一种浮游生物）的化学成分，特别是它们的氮和硅成分，反映了过去地表水营养物质和植物吸收的变化。南大洋沉积硅藻氮和硅值的变化记录了海洋生物在多大程度上消耗了海洋表面的营养物质。这些记录被解释为记录了大尺度垂直海洋环流的变化以及铁刺激的生物生产。这些过程可能共同促进了海洋和大气之间的碳交换。拟议的工作将解决我们对硅藻代用品如何记录地表营养条件的理解差距。具体来说，这包括对环境控制的生理影响的研究，这些影响导致硅藻改变它们如何构建外壳，以及在下沉和掩埋期间的变化对氮和二氧化硅组成的潜在影响。该结果将改进过去的养分衰减重建，突出可靠重建的最佳地质条件，并增加我们对现有硅藻氮和硅同位素记录的观测时空变化的理解。这项工作将最终提高我们对过去全球尺度气候变化的理解，并为未来的变化提供背景。该项目将促进早期职业科学家的职业生涯，通过培训学生和将项目成果纳入课程作业来影响教育，并通过艺术将该项目的科学方法，目标和结果转化为新的受众。这项工作将研究：1)南大洋春季水华期间硅藻氮和硅同位素值与表面营养吸收之间的关系；2)硅藻结合的营养同位素代用物、常量营养素和生物量之间关系的空间变异性的主要控制因素；3)向沉积物转移过程中同位素信号可能发生的改变。现场组件包括67°S至54°S的样带，用于对水和颗粒进行广泛采样。结合同位素和新型荧光标记技术的船上孵育将测量硅藻氮和硅同位素的硅藻硅化程度的影响。将通过在家庭机构的实验室孵育来评估微硅化分类群的丧失和/或分离对小菌落溶解的影响。艺术与科学合作的成果将在网上和活动中公开展示。我们将通过参与海洋学研究生院的本科生研究经验和海洋学暑期本科生研究奖学金项目，扩大罗德岛大学对STEM的参与，并在该项目的研究生职位招聘中优先考虑代表性不足的群体，并通过专注于服务不足的K-12学生的研究经验和教育设施，在加州大学圣巴巴拉分校招聘代表性不足的群体。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。

The chemistry of fossil diatoms (a type of plankton), specifically their nitrogen and silicon composition, reflects past changes in surface water nutrients and uptake by plants. Changes in sedimentary diatom nitrogen and silicon values from the Southern Ocean record to what degree ocean biology consumed nutrients in the surface ocean through time. These records have been interpreted to document changes in large-scale vertical ocean circulation as well as iron-stimulated biological production. These processes likely worked together to contribute to carbon exchange between the ocean and the atmosphere. The proposed work will address gaps in our understanding of how the diatom proxies record surface nutrient conditions. Specifically, this includes an examination of environmentally controlled effects on physiology that lead diatoms to change how they build their shells and of alteration during sinking and burial as potential influences on the composition of nitrogen and silica. The results will improve reconstructions of nutrient drawdown in the past, highlight optimal geological conditions for robust reconstructions, and increase our understanding of observed spatial and temporal variability in existing diatom nitrogen and silicon isotope records. This work will ultimately improve our understanding of global-scale climate change in the past and contextualize future change. The project will foster the careers of early career scientists, impact education through training of students and incorporation of project results into course work, and translate science methods, goals, and results of this project to novel audiences through art. The proposed work will examine: 1) the relationship between diatom nitrogen and silicon isotope values and surface nutrient uptake during a Southern Ocean spring bloom, 2) primary controls on the spatial variability observed for the relationships between diatom-bound nutrient isotope proxies, macronutrients, and biomass, and 3) possible alteration to isotopic signals occurring during transit to the sediment. The field component includes a transect from 67°S to 54°S to conduct extensive sampling of water and particles. Shipboard incubations combining isotope and novel fluorescent labeling techniques will measure how degree of silicification influences diatom Nitrogen and Silica isotopes. The influence of the loss of lightly silicified taxa and/or fractionation during the dissolution of frustules will be evaluated through laboratory incubations at home institutions. Products of an art-science collaboration will be publicly displayed online and at events. We will broaden participation in STEM at the University of Rhode Island through our participation in the Graduate School of Oceanography’s Research Experience for Undergraduates and the Summer Undergraduate Research Fellowship in Oceanography Program, as well as prioritizing underrepresented groups in recruitment for the project’s graduate student position and at University California Santa Barbara through the Research Experience and Education Facility that focuses on underserved K-12 students.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.