Collaborative Research: GEOTRACES Peru-Tahiti Nitrogen Isotope Measurements

氮(N)是一种基本的常量营养素，其可获得性会限制初级生产量和生物泵在季节、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(生物有效)氮的清单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(ODZ)是固定N损失和N2O产生的重要场所，随着全球变暖增加海洋分层和减少通风，预计它们在未来几年将扩大和加强。重要的是要了解硝酸盐、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有效性顺序的关系，以解释硝酸盐ä15N信号过去和未来的变化。在这个项目中，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一组研究人员将测量沿GEOTRACES太平洋秘鲁-塔希提岛段采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)。Del15N和del18O的值也将在气溶胶和降雨样本的硝酸盐中进行测量，以帮助我们解释热带南太平洋内的N同位素收支和同位素梯度。最后，将确定N_2/Ar和N_2/Ar和N_2del15N以接近N质量和同位素预算。硝酸盐del15N是GEOTRACES的一个“核心参数”，它将补充其他测量方法，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指标。GEOTRACES秘鲁-塔希提岛段提供了一个难得的机会来追踪来自最大的水柱ODZ之一的氮损失的同位素信号的命运。此外，人们对通过热液喷口循环的氮对深海硝酸盐同位素的影响知之甚少，这一部分将使我们能够对这一输入进行定量跟踪。总而言之，这些测量将深入了解现代N循环过程的相对速率，并将为古海洋学应用提供背景信息。广泛影响：该项目将提供南太平洋采样不足部分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达特茅斯大学最先进的合作研究。该项目还将支持为斯坦福大学地球学院举办的年度六年级教师讲习班开发和实施海洋部分。该计划包括对教师在地球科学和海洋学方面的前沿研究的指导，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.