Of all the biogeochemical cycles, nitrogen is the one most intimately and thoroughly associated with microbes. Essential and unique steps in the nitrogen cycle are performed by a wide array of bacteria, archaea, and eukaryotes, and the broad outlines of the cycle have been understood for over a century. That is why recent discoveries, in both terrestrial and aquatic environments, have surprised and intrigued the biogeochemical community. In this article, we focus on a few of the most exciting, very recent developments in the nitrogen cycle, summarize the changes in our understanding, and point out some questions to guide future research. The main processes of interest are anaerobic ammonium oxidation (anammox), aerobic nitrification by archaea, nitrogen fixation by unicellular marine cyanobacteria, and the issue of the balance and coupling between internal input and removal pathways. The nitrogen cycle in marine environments (Figure 1), in whole and in all of it various parts, is thoroughly reviewed in the recent revision of Nitrogen in Marine Environments (Capone et al., in press).

Ward, B.B., D.G. Capone, and J.P. Zehr. 2007. What’s new in the nitrogen cycle? Oceanography 20(2):101–109, https://doi.org/10.5670/oceanog.2007.53.

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