Collaborative Research: GEOTRACES Peru-Tahiti Nitrogen Isotope Measurements

氮（N）是一种必需的常量营养素，其可用性可以限制初级生产和生物泵在季节，年度，十年和千年时间尺度上从海洋表面输出碳的能力。海洋中固定（生物可利用）氮的存量是由生物过程驱动的，如固氮、反硝化和厌氧氨氧化（anammox）。水柱缺氧区（ODZs）是固定氮损失和N2 O产生的重要场所，随着全球变暖增加海洋分层和减少通风，它们预计将在未来几年扩大和加强。了解硝酸盐、亚硝酸盐和N2 O同位素的分布与当前海洋氧和微量元素可用性条件的关系，以解释硝酸盐15 N信号过去和未来的变化是很重要的。在这个项目中，来自斯坦福大学、马萨诸塞州大学达特茅斯分校和布朗大学的一组研究人员将测量沿着GEOTRACES太平洋秘鲁-塔希提段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（del 15 N和del 18 O）。del 15 N和del 18 O的值也将被测量的硝酸盐气溶胶和雨水样品，以告知我们的解释的N同位素预算和同位素梯度在热带南太平洋。最后，N2/Ar和N2 del 15 N将被确定为接近N质量和同位素收支。硝酸盐del 15 N是GEOTRACES的“核心参数”，将补充其他测量，如生物活性微量元素浓度和形态，Si同位素变化，以及氧化还原和生产率代理。GEOTRACES秘鲁-塔希提岛部分提供了一个难得的机会来跟踪最大的水柱臭氧消耗区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的氮再循环对深海硝酸盐同位素的影响知之甚少，本节将对这一输入进行定量跟踪。总之，这些测量将产生洞察到现代N循环过程的相对速率，并将提供背景信息为paleoceanographicapplication.Broader的影响：该项目将提供一个高品质的硝酸盐同位素数据集，从采样不足的部分南太平洋使用的更广泛的海洋社区通过BCO-DMO。 教育影响包括指导斯坦福大学的研究生、本科生和高中生，以及将本科生纳入布朗大学和麻省大学达特茅斯分校最先进的合作研究。该项目还将支持为斯坦福大学地球学院每年举办的六年级教师讲习班制定和实施海洋部分。该计划包括为教师提供地球科学和海洋学前沿研究的指导，并支持他们将材料纳入课堂活动。

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.