The distribution and metabolism of urea in the eastern Canadian Arctic

Urea concentrations, uptake, and excretion were measured at various locations in northern Baffin Bay and surrounding waters during the summer of 1980. Concentrations were variable ( 2.00 mg-at. N m−3) but followed patterns of decreasing concentration with depth in the euphotic zone and with distance from land. Urea accounted for > 50% of the total dissolved nitrogen in the upper mixed layer at most stations. Urea uptake rates showed generally the same distributional patterns as did concentrations and on the average accounted for 32% of the total nitrogen (NO3− + NH4+ + urea) productivity in the eupholic zone. Ammonium, and frequently NO3−, were utilized in preference to urea. Dual isotope (14C and 15N-urea) labelling experiments suggested that most urea-C was respired as CO2 while 50 to 80% of the urea-N was incorporated by the phytoplankton. Excretion measurements suggested that the four dominant macrozooplankton species (Calanus hyperboreus, C. finmarchicus, C. glacialis, and Metridia sp.) supplied only −3% of the urea-N but –40% of the NH4+-N requirements of the primary producers.