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

化石硅藻(浮游生物的一种)的化学成分，特别是它们的氮和硅组成，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随着时间的推移，海洋生物消耗表层海洋营养物质的程度。这些记录被解释为记录了大规模垂直海洋环流以及铁刺激的生物生产的变化。这些过程很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替代物如何记录表面营养条件的理解上的空白。具体地说，这包括检查环境控制对生理的影响，导致硅藻改变它们建造贝壳的方式，以及下沉和埋葬过程中的变化，作为对氮和二氧化硅组成的潜在影响。这些结果将改进过去营养盐下降的重建，突出稳健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中观察到的空间和时间变异性的理解。这项工作最终将提高我们对过去全球范围气候变化的理解，并为未来的变化提供背景信息。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工作来影响教育，并通过ART将该项目的科学方法、目标和结果转化为新的受众。拟议的工作将检查：1)在南大洋春季水华期间硅藻氮和硅同位素值与表层养分吸收之间的关系，2)对硅藻结合的营养同位素代用品、常量营养素和生物量之间关系所观察到的空间变异性的基本控制，以及3)在向沉积物转移过程中发生的同位素信号的可能变化。该场分量包括一条从67°S到54°S的断面，用于对水和颗粒进行广泛的采样。结合同位素和新的荧光标记技术的船上培养将测量硅化程度如何影响硅藻、氮和二氧化硅同位素。将通过国内机构的实验室培养来评估在小果溶解过程中损失的轻度硅化分类群和/或分级的影响。艺术与科学合作的产品将在网上和活动中公开展示。我们将通过参与海洋研究生院的本科生研究经历和夏季本科生海洋学研究奖学金项目，以及在加州大学圣巴巴拉大学通过专注于服务不足的K-12学生的研究经验和教育基金，优先招收该项目研究生职位和加州大学圣巴巴拉大学的代表不足的群体，扩大我们对罗德岛大学STEM的参与。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.