Collaborative Research: GEOTRACES Peru-Tahiti Nitrogen Isotope Measurements

氮 (N) 是一种必需的大量营养素，其可用性会限制初级生产以及生物泵在季节性、年度、十年和千年时间尺度上从表层海洋输出碳的能力。海洋中固定（生物可利用）氮的库存是由固氮、反硝化和厌氧氨氧化（厌氧氨氧化）等生物过程驱动的。水柱缺氧区 (ODZ) 是固定氮损失和 N2O 产生的重要场所，随着全球变暖增加海洋分层和通风减少，预计未来几年这些缺氧区将扩大和加剧。了解硝酸盐、亚硝酸盐和 N2O 同位素的分布与当前海洋氧气条件和微量元素可用性的关系非常重要，以便解释硝酸盐 ä15N 信号过去和未来的变化。在该项目中，来自斯坦福大学、马萨诸塞大学达特茅斯分校和布朗大学的研究人员团队将测量沿着 GEOTRACES 太平洋秘鲁-塔希提岛剖面收集的海水样本中硝酸盐、亚硝酸盐和一氧化二氮的氮和氧同位素组成（del15N 和 del18O）。还将测量气溶胶和雨水样本中硝酸盐的 del15N 和 del18O 值，以帮助我们解释热带南太平洋内的 N 同位素预算和同位素梯度。最后，将确定 N2/Ar 和 N2 del15N 以关闭 N 质量和同位素预算。硝酸盐 del15N 是 GEOTRACES 的“核心参数”，它将补充其他测量，例如生物活性微量元素浓度和形态、硅同位素变化以及氧化还原和生产力代理。 GEOTRACES 秘鲁-塔希提岛部分提供了一个难得的机会来跟踪最大水体 ODZ 之一的氮损失同位素信号的命运。此外，人们对通过热液喷口进行氮循环对深海硝酸盐同位素的影响知​​之甚少，本节将允许定量跟踪这种输入。总之，这些测量将深入了解现代氮循环过程的相对速率，并为古海洋学应用提供背景信息。更广泛的影响：该项目将提供来自南太平洋欠采样地区的高质量硝酸盐同位素数据集，供更广泛的海洋学界通过 BCO-DMO 使用。 教育影响包括对斯坦福大学研究生、本科生和高中生的指导，以及让本科生参与布朗大学和麻省大学达特茅斯分校最先进的合作研究。该项目还将支持斯坦福大学地球学院举办的年度六年级教师研讨会的海洋部分的开发和实施。该计划包括对教师进行地球科学和海洋学前沿研究的指导，并支持他们将这些材料纳入课堂活动。

Nitrogen (N) is an essential macronutrient whose availability can limit primary production and the capacity of the biological pump to export carbon from the surface ocean on seasonal, annual, decadal, and millennial timescales. The inventory of fixed (bioavailable) N in the ocean is driven by biological processes such as nitrogen fixation, denitrification, and anaerobic ammonia oxidation (anammox). Water column oxygen deficient zones (ODZs) are important sites for fixed N loss, as well as N2O production, and they are projected to expand and intensify in the coming years as global warming increases ocean stratification and decreases ventilation. It is important to understand the distribution of nitrate, nitrite, and N2O isotopes in relation to current ocean conditions of oxygen and trace element availability order to interpret past and future changes in nitrate ä15N signals. In this project, a team of researchers from Stanford University, University of Massachusetts at Dartmouth, and Brown University will measure the nitrogen- and oxygen-isotopic composition (del15N and del18O) of nitrate, nitrite, and nitrous oxide in seawater samples collected along the GEOTRACES Pacific Peru-Tahiti Section. Values of del15N and del18O will also be measured in nitrate from aerosol and rain samples to inform our interpretation of the N isotope budget and isotopic gradients within the tropical South Pacific. Finally, N2/Ar and N2 del15N will be determined to close the N mass and isotope budgets. Nitrate del15N is a GEOTRACES "core parameter" that will complement other measurements, such as bioactive trace element concentrations and speciation, Si isotope variations, as well as redox and productivity proxies. The GEOTRACES Peru-Tahiti section provides a rare opportunity to track the fate of the isotopic signals of N loss from one of the largest water column ODZs. Furthermore, little is known about the effect of N recycling through hydrothermal vents on nitrate isotopes in the deep ocean, and this section will allow quantitative tracking of this input. Together, these measurements will yield insight into the relative rates of modern N cycle processes and will provide background information for paleoceanographic applications.Broader impacts: This project will provide a high-quality nitrate isotope data set from undersampled parts of the South Pacific for use by the broader oceanographic community via BCO-DMO. Educational impacts include the mentoring of a graduate, undergraduate, and high school students at Stanford, and the inclusion of undergraduates in state-of-the-art collaborative research at Brown and UMass-Dartmouth. The project will also support development and implementation of an oceans component for the annual 6th grade teacher workshop offered by Stanford University's School of Earth. This program includes both instruction for the teachers on cutting-edge research in Earth Science and Oceanography, and support for them to include the material into their classroom activities.