Collaborative Research: ETBC--The Cycling of Nitrogen in an Earth System Model: Constraints and Implications for Climate Change

该项目的总体目标是：1)通过数值模拟、数据综合和分析相结合，限制活性氮（Nr）的全球预算；2)对活性氮循环与气候之间的总体相互作用进行初步估计。氮循环是地球气候系统的关键调节器，连接着陆地、海洋、光化学和工业过程，并调节着碳循环。在过去的一个半世纪里，农业和化石燃料燃烧的扩张和强化导致向大气排放的Nr增加了一倍多，对地球系统产生了深远的影响。在CCSM（社区气候系统模式）中，通过跟踪三个模式域的Nr来模拟一个封闭的全球Nr循环：(1)大气，(2)陆地，包括原生和农业生态系统，以及(3)淡水和海洋。虽然这项工作的大部分基础已经在CCSM中得到了发展，但氮循环还没有在不同的模型域中耦合。在全耦合系统中，每个模型域将模拟其域内Nr的输运和生成以及其域内Nr的化学性质和损失，并要求域间的氮通量自一致。这种质量平衡的方法将避免在单个域内孤立地模拟氮循环时发生的未跟踪的Nr损失。此外，还将考虑Nr对陆地碳汇以及对辐射重要物种氧化亚氮、臭氧、甲烷和气溶胶硫酸铵的不同和相反的影响。据推测，变化的Nr循环对这四种大气物种的总体影响将导致足够的变暖，以抵消与增加的Nr可用性和增加的陆地碳吸收量相关的冷却。用于评估地球系统模式中氮循环的综合数据集、本文开发的氮-碳-气候耦合模式以及CCSM模拟将广泛提供给大学和国家实验室社区，并将为即将到来的IPCC第五次评估做出贡献。本项目的主要研究人员大多积极从事研究生教育和培训工作，也大多参加本科生活动。这项研究将支持另外四名研究生和一名博士后以及一些本科生。所有人都将在各自的当地机构以及参与该项目的所有机构和学科参与研究活动。

The overarching goals of this project are: 1) to constrain the global budget of reactive nitrogen (Nr) through a combination of numerical simulations, data synthesis and analysis; and 2) to produce initial estimates of the overall interaction between reactive nitrogen cycling and climate. The nitrogen cycle is a key regulator of the Earth's climate system, linking terrestrial, marine, photochemical, and industrial processes, and modulating the carbon cycle. Over the last century and a half, expansion and intensification of agriculture and fossil fuel combustion have led to a more than doubling of Nr emissions to the atmosphere with profound impacts on the earth system. A closed global Nr cycle will be simulated within the CCSM (Community Climate System Model) by tracking Nr across three model domains: (1) atmosphere, (2) land, including native and agroecosystems, and (3) fresh and oceanic waters. While the basis for much of this work has already been developed within the CCSM, the nitrogen cycle has not been coupled across the different model domains. In the fully coupled system, each model domain will simulate the transport and production of Nr within its domain and the chemistry and loss of Nr from its domain, with the requirement that the nitrogen fluxes between the domains be self-consistent. This mass-balanced approach will avoid the untracked losses of Nr that occur when the nitrogen cycle is modeled in isolation within a single domain. Moreover, it will consider the diverse and opposing impacts of Nr on terrestrial carbon sinks and on the radiatively important species nitrous oxide, ozone, methane and aerosol ammonium sulfate. It is hypothesized that the overall effect of a changing Nr cycle on these four atmospheric species will lead to a warming sufficient to offset the cooling associated with increased Nr availability and increased terrestrial carbon uptake.The synthesized datasets for evaluating the nitrogen cycle in Earth System Models, the coupled nitrogen-carbon-climate model developed here, and the simulations with the CCSM will be made broadly available to university and national laboratory communities and will contribute to the upcoming IPCC 5th Assessment. Most of the principal investigators in this project are actively engaged in graduate student education and training, and most participate in undergraduate activities as well. The research will support four additional graduate students and one postdoctoral associate as well as a number of undergraduates. All will become involved in the research activities both at their respective local institutions, as well as across all institutions and disciplines involved in the project.