School of Oceanography, University of Washington, Seattle, Washington 98195-5351; email:
Ann Rev Mar Sci. 2015;7:403-23. doi: 10.1146/annurev-marine-010213-135040.
Fixed nitrogen limits primary productivity in many parts of the global ocean, and it consequently plays a role in controlling the carbon dioxide content of the atmosphere. The concentration of fixed nitrogen is determined by the balance between two processes: the fixation of nitrogen gas into organic forms by diazotrophs, and the reconversion of fixed nitrogen to nitrogen gas by denitrifying organisms. However, current sedimentary denitrification rates are poorly constrained, especially in permeable sediments, which cover the majority of the continental margin. Also, anammox has recently been shown to be an additional pathway for the loss of fixed nitrogen in sediments. This article briefly reviews sedimentary fixed nitrogen loss by sedimentary denitrification and anammox, including in sediments in contact with oxygen-deficient zones. A simple extrapolation of existing rate measurements to the global sedimentary denitrification rate yields a value smaller than many existing measurement-based estimates but still larger than the rate of water column denitrification.
固定氮在全球海洋的许多地区限制了初级生产力，因此在控制大气二氧化碳含量方面发挥了作用。固定氮的浓度取决于两个过程之间的平衡：固氮生物将氮气固定为有机形式，以及反硝化生物将固定氮重新转化为氮气。然而，目前的沉积物反硝化速率受到很大限制，特别是在渗透性沉积物中，它们覆盖了大陆架的大部分地区。此外，最近的研究表明，氨氧化是沉积物中固定氮损失的另一种途径。本文简要回顾了沉积物反硝化和氨氧化作用导致的沉积物固定氮损失，包括与缺氧区接触的沉积物。将现有速率测量值简单外推到全球沉积物反硝化速率，得到的值小于许多基于现有测量的估计值，但仍大于水柱反硝化速率。
