Collaborative Research: US GEOTRACES PMT: Investigating geochemical tracers of the Pacific nitrogen cycle and budget

硝酸盐是海洋植物和藻类生长所需的重要营养物质。它在深海中很丰富，但在大多数阳光普照的表层水域却很稀少。这个项目的目的是为了更好地了解是什么控制着深海中硝酸盐的可用性及其向地表水的输送。斯坦福大学、普林斯顿大学和布朗大学的研究人员将分析在阿拉斯加和太平洋塔希提岛之间收集的海水硝酸盐的稳定同位素。这些数据将提供有关太平洋大部分地区硝酸盐供应的信息，并允许对海洋光合作用过去和未来的变化作出明智的决定。该合作项目将在GEOTRACES项目下进行，该项目是一项了解全球海洋元素分布的国际努力。这项研究将包括所有三个学术机构的本科生、研究生和博士后研究人员。研究人员将为普林斯顿大学的初中和高中教师开展为期一天的教师学者项目研讨会。讲习班将侧重于获取和可视化海洋数据集和互联网上可获得的其他内容，以便在课堂上进行基于项目的学习。调查人员还将参加每年夏天在斯坦福大学举办的教师研讨会。该项目的数据将通过生物和化学海洋学数据管理处（www.bco-dmo.org）向公众提供。这些数据还将汇编在GEOTRACES数据产品中，这些产品将免费提供。海洋内部硝酸盐同位素组成记录了年、几十年、几百年和几千年时间尺度上的生物地球化学和物理过程，其中浅海记录的时间尺度较短，深海记录的时间尺度较长。这些都是有意义的时间尺度，有助于(1)了解海洋中氮的生物地球化学、海洋生产力和全球碳循环的反馈结构，(2)重建海洋生物地球化学和碳循环的过去变化，以及(3)预测未来的变化。本提案旨在分析阿拉斯加和塔希提岛之间即将到来的美国GEOTRACES太平洋经向样带（GP15）期间的硝酸盐同位素。硝酸盐同位素对海洋氮循环和平衡提供了关键的限制，特别是在太平洋，各种过程影响硝酸盐的分布及其向地表水的供应。作为不断增长的全球海洋硝酸盐同位素数据集的一部分，这种主要是经向剖面的硝酸盐同位素数据将具有广泛的用途，并可与作为GEOTRACES工作的一部分将生成的许多互补的地球化学数据集进行比较。此外，将测量气溶胶中的硝酸盐同位素，以支持对该剖面地表水中硝酸盐同位素的解释。提出的测量方法将有助于研究三个主要问题：1)太平洋盆地不同营养丰富地区（南大洋、赤道太平洋和亚北极北太平洋）氮生物地球化学的异同，以及它们如何影响低纬度地表水的硝酸盐供应？2)跨太平洋地表水的氮燃料出口生产有哪些来源？3)表层和次表层过程在海洋内部硝酸盐同位素分布中的作用是什么？

Nitrate is an important nutrient that marine plants and algae need for growth. It is abundant in deep ocean waters, but scarce in most sunlit surface waters. The purpose of this project is to better understand what controls the availability of nitrate in the deep ocean and its delivery to surface waters. Researchers from Stanford University, Princeton University, and Brown University will analyze the stable isotopes of seawater nitrate collected between Alaska and Tahiti in the Pacific Ocean. The data will provide information about the supply of nitrate to a large section of the Pacific Ocean and allow informed decisions on past and future changes in marine photosynthesis. This collaborative project will be carried under the GEOTRACES program, an international effort to understand the distribution of elements in the global ocean. This study will include undergraduate, graduate, and postdoctoral researchers at all three academic instititutions. The investigators will develop a 1-day workshop for the Teachers as Scholars program, for middle and high school teachers at Princeton University. The workshop will focus on accessing and visualizing ocean data sets and other content available on the internet for project-based learning in the classroom. Investigators will also participate in teacher workshops offered each summer at Stanford University. Data from this project will be made available to the public through the Biological and Chemical Oceanography-Data Management Office (www.bco-dmo.org). The data will also be compiled in GEOTRACES data products that will be freely available.The isotopic composition of nitrate in the ocean interior records biogeochemical and physical processes on the time scales of years, decades, centuries, and millennia, with the shallow subsurface and deep ocean recording shorter and longer time scales, respectively. These are meaningful time scales in the efforts to (1) understand the feedbacks that structure the biogeochemistry of N in the ocean, ocean productivity, and the global carbon cycle, (2) reconstruct past changes in ocean biogeochemistry and carbon cycling, and (3) perhaps predict future changes. This proposal seeks to analyze the nitrate isotopes during the upcoming US GEOTRACES Pacific Meridional Transect (GP15) between Alaska and Tahiti. Nitrate isotopes provide critical constraints on the ocean N cycle and budget, especially in the Pacific Ocean where a variety of processes affect the distribution of nitrate and its supply to surface waters. This largely meridional section of nitrate isotope data will be broadly useful as part of the growing nitrate isotope dataset for the global ocean and for comparison to the many complementary geochemical data sets that will be generated as part of this GEOTRACES effort. In addition, nitrate isotopes in aerosols will be measured to support interpretations of nitrate isotopes in surface waters along the section. The proposed measurements will contribute to the investigation of three overarching questions: 1) What are the similarities and differences in N biogeochemistry among the different nutrient-rich regions in the Pacific basin: the Southern Ocean, equatorial Pacific, and subarctic North Pacific, and how do they affect nitrate supply to low-latitude surface waters? 2) What sources of nitrogen fuel export production in surface waters across the Pacific? 3) What are the roles in surface and subsurface processes in the distribution of nitrate isotopes in the ocean interior?