The Marine Nitrogen Cycle

This chapter serves as an introduction to rest of the book. The focus here is on providing an overview of the most important pools of nitrogen, their transformations, their distribution, and their connection to the cycling of other biogeochemically relevant elements, primarily carbon, oxygen, and phosphorus. The scale is global, as subsequent chapters cover individual ocean basins and systems. The chapter also addresses a series of nitrogen challenges, such as the question of how the marine nitrogen cycle appears to be able to maintain a relatively well-established homeostasis, that is, a balance between gains and losses of fixed nitrogen. Finally, it discusses the anthropogenic perturbation of the marine nitrogen cycle. As it examines, however, the answers to many of these questions remain elusive, reminding us how little we know about the marine nitrogen cycle, and how much still remains to be discovered. Although the marine nitrogen cycle occupies a central role within the biogeochemical cycles of the sea, scientific communities barely begin to its major processes and the factors that regulate them. This occurs at a time when human interventions in the Earth system rise to unprecedented levels, with a particularly strong impact on the global nitrogen cycle.