Nutrients and organic nitrogenous compounds in the marginal ice zone of the Fram Strait

Abstract

During the summer of 1988 the distribution of nutrients and organic nitrogenous substances were studied in the Fram Strait area as part of the Greenland Sea project. The marginal ice zone with the Polar and Arctic Front was clearly determined by the hydrography and nutrient distribution. In the surface layer of the Arctic and Atlantic Water, nitrate was depleted. In the nutricline which was at about 30 to 50 m and below, ammonium maxima occurred. In the surface layer of the ice-covered Polar Water, nitrate was still available with about 4 μM/l. Particulate organic nitrogen was restricted to the nitrate depleted upper-water layer with values of about 3 μM/l. Concentrations of dissolved organic nitrogen (DON) were enriched in the surface layer with more than 5 μM/l but were not significantly different in the water masses. In contrast, the free amino acids followed much closer the frontal situation but contributed only less than 3% to the DON. The proportion of total dissolved amino acids was much higher with about 20% of DON. In the deeper layers below 500 m the concentrations and compositions were more uniform. High nitrate values and only about half of the DON compared to the surface layer were found. Total amino acids were low or around the detection limit. The results show that DON plays an important role in budget calculations and that a considerable part belongs to a DON fraction which may maintain a certain phytoplankton stock during nitrate depletion.