Nitrogen uptake rates in phytoplankton and ice algae in the Barents Sea

Abstract

Uptake rates of NH4+, NO3? and dissolved organic nitrogen (urea) were measured in phytoplankton and in ice algae in the Barents Sea using a 15N-technique. NO3? was the most important nitrogen source for the ice algae (f-ratio = 0.92). The in situ irradiances in the subsurface chlorophyll maximum and in the ice algal communities were low. The in situ NO3? uptake rate in the ice algal communities was light-limited The in situ NO3? and NH4? uptake rates in the subsurface chlorophyll maximum were at times light-limited. It is hypothesised that NH4+ may accumulate in low light in the bottom of the euphotic zone and inhibit the in situ NO3? uptake rate.