ACTIVATION OF NITRATE UPTAKE DUE TO PHOSP HATE ADDITION IN THE WATERSOF THE TROPICAL ATLANTIC-OCEAN

The utilization of a sensitive automatic method for nitrate analysis h as been applied to study the influence of phosphate on nitrate uptake in surface seawater samples collected in an oligotrophic area (Tropica l Atlantic Ocean). The deck-incubation experiments performed during mo re than 24 h showed a strong phosphate-stimulation of the nitrate cons umption after a delay of 12 to 24 h. The nitrate uptake is increased b y a factor of 3 to 6. The experiments described here demonstrate that : (1) planktonic organisms that take up the nitrate are phosphorus-def icient in this oligotrophic area ; (2) phosphorus may be a limiting fa ctor for the new production ; (3) phosphorus takes an important part i n the nitrogen dynamics in the ocean.