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。它在深海沃茨中含量丰富，但在大多数阳光照射的表层沃茨中含量稀少。该项目的目的是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沃茨的输送。来自斯坦福大学、普林斯顿大学和布朗大学的研究人员将分析在太平洋阿拉斯加和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做出明智的决定。这一合作项目将在GEOTRACES计划下进行，该计划是一项旨在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发一个为期一天的教师学者项目研讨会。讲习班将侧重于访问和可视化海洋数据集和互联网上提供的其他内容，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办公室（www.bco-dmo.org）向公众提供。海洋内部硝酸盐的同位素组成记录了以年、几十年、几百年和几千年为时间尺度的地球化学和物理过程，浅地下和深海分别记录了较短和较长的时间尺度。这些都是有意义的时间尺度，努力（1）了解结构的反馈海洋中的N，海洋生产力和全球碳循环，（2）重建过去的变化在海洋地球化学和碳循环，（3）也许预测未来的变化。该提案旨在分析阿拉斯加和塔希提岛之间即将进行的美国GEOTRACES太平洋子午线断面（GP15）期间的硝酸盐同位素。硝酸盐同位素对海洋氮循环和收支提供了重要的限制，特别是在太平洋，各种过程影响硝酸盐的分布及其向表层沃茨的供应。硝酸盐同位素数据的这一大部分是非对称的，将作为全球海洋不断增长的硝酸盐同位素数据集的一部分，并与作为GEOTRACES工作的一部分而产生的许多补充地球化学数据集进行比较，这将是广泛有用的。此外，还将测量气溶胶中的硝酸盐同位素，以支持对剖面沿线沿着水沃茨中硝酸盐同位素的解释。建议的测量将有助于调查的三个首要问题：1）在太平洋盆地的不同营养丰富的地区之间的氮的地球化学的相似性和差异：南大洋，赤道太平洋，和亚北极北太平洋，以及它们如何影响硝酸盐供应低纬度表面沃茨？2)太平洋表面沃茨的氮燃料出口生产的来源是什么？3)在海洋内部硝酸盐同位素分布的表面和次表面过程中有什么作用？

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?