Cyanate distribution and uptake in North Atlantic coastal waters

Abstract

AbstractCyanate (OCN−) is a reduced nitrogen compound that may be a source of nitrogen and carbon for marine phytoplankton. Cyanate is produced photochemically and through organic matter degradation but its distribution in marine systems is poorly defined because, until recently, there was no method to measure its concentration in marine environments. Here, we report results from the first regional oceanographic survey of cyanate distributions and uptake. Cyanate concentrations ranged from below detection (0.4 nM) to 11 nM in the coastal North Atlantic Ocean along the North American continental shelf and were slightly higher in nearshore surface waters than offshore surface waters. Subsurface cyanate maxima were observed at many stations suggesting a nonconservative distribution. Subsurface cyanate peak concentrations were tightly correlated with chlorophyll a concentrations integrated throughout the water column (R2 = 0.79). Cyanate N and C uptake were measurable in all regions and seasons sampled. Cyanate N uptake was significantly higher than cyanate C uptake for all cruises (1.3 ± 1.9 nmol L−1 h−1 and 0.4 ± 0.6 nmol L−1 h−1 for N and C, respectively). However, cyanate N uptake was significantly lower in November than in June and August, and cyanate C uptake was significantly higher in November than during June and August. Spatial trends in cyanate distribution and uptake, along with the correlation between depth‐integrated Chl a concentrations and cyanate maxima, suggest that cyanate is taken up in the euphotic zone and is likely produced by degradation of phytoplankton‐derived organic matter in subsurface waters.