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)通过结合数值模拟、数据合成和分析来限制全球活性氮(Nr)的预算；以及2)对活性氮循环与气候之间的整体相互作用做出初步估计。氮循环是地球气候系统的关键调节器，将陆地、海洋、光化学和工业过程联系起来，并调节碳循环。在过去的一个半世纪里，农业和化石燃料燃烧的扩大和强化导致向大气排放的Nr增加了一倍以上，对地球系统产生了深远的影响。一个封闭的全球Nr循环将在CCSM(社区气候系统模式)中通过跟踪三个模型域的Nr来模拟：(1)大气，(2)陆地，包括自然和农业生态系统，(3)淡水和海洋水域。虽然这项工作的大部分基础已经在CCSM内开发，但氮循环还没有跨不同的模型域耦合。在全耦合系统中，每个模型区域将模拟Nr在其区域内的传输和生产，以及Nr在其区域中的化学和损失，要求区域之间的氮通量是自洽的。这种质量平衡的方法将避免在单个区域内孤立地模拟氮循环时发生的未跟踪的Nr损失。此外，它还将考虑Nr对陆地碳汇以及对具有辐射重要性的物种一氧化二氮、臭氧、甲烷和气溶胶硫酸铵的不同和相反的影响。假设变化的Nr循环对这四个大气物种的总体影响将导致气候变暖，足以抵消与Nr可用性增加和陆地碳吸收增加相关的冷却。用于评估地球系统模型中氮循环的综合数据集、这里开发的氮-碳-气候耦合模型以及与CCSM的模拟将广泛地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。该项目的主要研究人员大多积极参与研究生教育和培训，并参与本科生活动。这项研究将支持另外四名研究生和一名博士后助理以及一些本科生。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.