UPTAKE OF NITRATE AND AMMONIA IN THE SUB-ARCTIC BOUNDARY AND ADJACENT REGIONS OF THE NORTHWESTERN PACIFIC-OCEAN

Nitrate and ammonia uptake rates were measured in summer at several stations in subarctic, subtropical and transitional regions of the North Pacific Ocean. Nitrate uptake rates (rho-NO3) and activity (rho-NO3/Chl a) were higher in subarctic and transitional regions than in the subtropical region. Ammonia uptake rates (rho-NH4) showed no remarkable regional pattern. Highest values of ammonia uptake activity (rho-NH4/Chl a) were observed in the subtropical region; values in the other areas were consistently lower. Nitrate was an equally important nitrogen source in subarctic and transitional regions, while ammonia was the main source in the subtropical region. In addition, data indicate that nitrogen uptake in the transitional region was more efficient than in the other regions. It is suggested that higher light intensity and temperature induced the higher degree of efficiency.