Reactive Nitrogen Cycling in the Atmosphere and Ocean

摘要

The budget of reactive nitrogen (Nr; oxidized and reduced inorganic and organic forms of nitrogen) has at least doubled since the preindustrial era due to human activities. Excess Nr causes significant detrimental effects on many terrestrial and aquatic ecosystems; less is known about the impact on the open ocean. Nr deposition may already rival biological N-2 fixation quantitatively and will likely continue to rise. However, it is unclear how much of the Nr currently deposited to the ocean is external in origin. Understanding the importance of ocean Nr emissions versus external Nr deposition is key to quantifying the influence of deposition on ocean biogeochemistry and climate. This article reviews our understanding of the impacts of Nr deposition on the open ocean and the emissions of Nr from the ocean, placing particular emphasis on stable isotopes as a tool to investigate the surface ocean-lower atmosphere Nr cycle and its variations over time.