Nitrogen isotope fractionation and geological nitrogen cycle

轻稳定同位素已成为追踪物质来源和监测行星和地球科学中（生物）地球化学过程的常规和强大的工具。例如，碳同位素已被用于研究地球上各种时空尺度的碳循环。这一努力极大地促进了我们对地球地幔、地壳，特别是大气层的演化和相互作用的理解，其中温室气体二氧化碳的水平直接影响气候和环境。与此形成鲜明对比的是，氮的循环，一个在地球所有水库中与碳同样重要的成分，仍然知之甚少，尽管它的几个物种（NH3，N2 O，N2）也作为温室气体。这主要是由于（1）对控制氮迁移的关键过程中的氮同位素效应以及在不同压力-温度条件下的选址认识不足，以及（2）定义不同储层的氮属性的边界条件约束不足。（1）使用实验室和现场-基于在与重要的氮循环过程相关的各种温度下确定不同氮物质之间的氮同位素分馏的研究，例如非生物氮还原、铵-氨转化、氨脱气和矿物之间的铵交换。(2)澄清了在研究俯冲带大规模氮循环方面的不确定性，包括确定俯冲早期氮行为的特征和检测弧火山岩中再循环的地壳氮及其对全球地质氮循环的贡献。

Light stable isotopes have become a routine and robust tool to trace material sources and monitor (bio)geochemical processes in planetary and geosciences. For example, carbon isotopes have been used to examine the carbon cycle in various temporal and spatial scales on the Earth. This effort has significantly advanced our understanding of the evolution of and interaction between the Earth's mantle, crust, and particularly atmosphere, in which the level of greenhouse gas CO2 directly impacts the climate and environment. In striking contrast, the cycle of nitrogen, a component equally important as carbon in all Earth's reservoirs, is still poorly understood even though several of its species (NH3, N2O, N2) also act as greenhouse gases. This has been mainly attributed to (1) the poor knowledge of nitrogen isotope effects in key processes controlling nitrogen transfer and siting at different pressure-temperature conditions and (2) poorly constrained boundary conditions to define the nitrogen properties of different reservoirs.To fill this gap, this Discovery Program has two objectives:(1) use laboratory- and field-based investigations to determine the nitrogen isotope fractionations between different nitrogen species at a variety of temperatures related to important nitrogen cycling processes, such as abiotic nitrogen reduction, ammonium-ammonia transformation, ammonia degassing, and ammonium exchange between minerals.(2) clarify the uncertainties in the study of large-scale nitrogen cycling across subduction zones, including characterizing the nitrogen behavior in early subduction and detecting the recycled crustal nitrogen in arc volcanic rocks and their contributions to the global geological nitrogen cycle.