The Marine Cyanate Cycle

• Main Author: Widner, Brittany
• Format: Thesis
• Language: unknown
• Published: Old Dominion University Libraries 2016
• Subjects: Pacific; North Atlantic
• Online Access: https://dx.doi.org/10.25777/bdhy-2t83; https://digitalcommons.odu.edu/oeas_etds/1/

Cyanate (OCN-) is a reduced nitrogen compound with the potential to serve as a nitrogen and carbon source for marine microbes. Evidence from genomes and culture studies indicated that several marine cyanobacterial groups, including representatives of the globally important genera Synechococcus and Prochlorococcus, might be capable of cyanate assimilation. However, prior to this study, the distribution, bioavailability, and production pathways of cyanate were unknown in natural systems due to the absence of a sensitive cyanate assay; and the ability of organisms to assimilate cyanate on relevant timescales was unknown because we lacked a suitable tracer for measuring uptake. I developed a cyanate assay to measure cyanate concentrations in estuarine and seawater samples, and then measured distribution at sites in the coastal western temperate North Atlantic (NA) and eastern tropical South Pacific (ETSP) including the Oxygen Deficient Zone. Cyanate concentrations ranged from below the limit of detection (0.4 nM) to 65 nM in natural samples examined to date. Cyanate was produced photochemically and in senescent diatom cultures, but cyanate was not detectable in wet and dry offshore atmospheric deposition. Using a custom-synthesized 13C15N-labeled cyanate compound, I also measured rates of cyanate uptake by natural microbial communities in the NA and ETSP. Cyanate N uptake ranged from undetectable (< 0.02) to 13 nmol l-1 h-1 and was significantly higher than cyanate C uptake on all cruises. Cyanate N uptake was up to 10% of total measured N uptake at an offshore oligotrophic station in the NA but contributed a smaller fraction of total measured N uptake (< 2%) at coastal stations in the NA and ETSP. The results of this dissertation indicate that: 1) cyanate concentrations are measureable in the marine environment and cyanate has a biological-like distribution in marine systems; 2) cyanate is taken up in surface waters, probably by phytoplankton; 3) cyanate is produced photochemically in sunlit waters and from degradation of organic matter throughout the water column or through direct release by phytoplankton; and 4) cyanate is consumed in the mesopelagic region probably by either conversion to ammonium and then to nitrate or by cyanate-supported anaerobic ammonium oxidation (cyanammox) in oxygen deficient waters.