Award: OCE-1459698

Nitrogen (N) is thought to limit productivity in large parts of the ocean. Because productivity in much of the ocean is limited by N, the oceanic N cycle is linked to the uptake (and release) of carbon dioxide by the oceans and as such, is sensitive to many climate change drivers. We live in an era when many of Earth?s ecosystems are under increasing strain due to accelerating human exploitation and disruption of natural nutrient and carbon cycles. As a result of this project, we are discovering that cyanate plays a dynamic role in the oceanic N cycle and is bioavailable to marine microbes. Until now there was no method for estimating cyanate concentrations in seawater or its uptake by microorganisms. As part of this project, we have applied a sensitive method for measuring cyanate concentrations in seawater (Widner et al. 2013, Analytical Chemistry) and a tracer method using highly enriched (15N and 13C) cyanate to estimate its uptake by microorganisms. We provided the first cross-system comparison of cyanate concentrations and uptake by microbes. In addition, we made a detailed examination of environmental gradients in cyanate concentrations and compared cyanate concentrations and uptake kinetics with those of other bioavailable N compounds. We provided the first evidence that cyanate is photochemically formed in surface waters, at rates similar to those shown for ammonium photoproduction and the cyanate is produced during the degradation of organic matter. Additionally, we found that cyanate is taken up by mixed phytoplankton assemblages across diverse oceanic environments. Based on these results, we contend that cyanate contributes substantially to nitrogen cycling in both coastal and offshore marine environments. While not explicitly a part of this project, we used the cruise opportunities to expand our measurements of cyanate concentrations in the sea and examine rates of cyanate uptake and losses in the eastern tropical North and South Pacific Ocean associated with the oxygen deficient zones there. We discovered that cyanate was denitrified by marine microbes in oxygen deficient waters and dubbed this process ?cyanammox?. During our dedicated cruise for this project, we also facilitated research by NASA scientists. Because of the likely sources of its production and consumption, cyanate exhibits a nutrient like distribution in the environment. We continue to identify sources of cyanate in the environment and quantify rates at which it is produced and consumed. These observations may contribute to balancing the marine N budget and understanding the metabolic diversity of marine microbes in the ocean at present and the diversity of microbial metabolisms over Earth?s history. Our results also generate a multitude of questions that are likely to be fodder for decades of research to come. What are the dominant sources and sinks of cyanate in disparate marine environments? Is cyanate also involved in dissimilatory nitrogen losses from oxygen deficient oceanic systems? Which organisms produce and consume cyanate, and does this change depending on environmental conditions? Might this simple compound have been important in the evolution of life? Is cyanate also an important participant in nitrogen cycling in freshwater and terrestrial systems? Are there agricultural, urban, and industrial sources of cyanate? These questions are of interest not only to marine biogeochemists but also to freshwater and terrestrial biogeochemists; environmental chemists, engineers, and microbiologists; molecular biologists and evolutionary biologists; geobiologists and paleochemists; and astrobiologists. Last Modified: 06/02/2019 Submitted by: Margaret R Mulholland