Nutrient flux fuels the summer primary productivity in the oligotrophic waters of the Gulf of Aqaba, Red Sea

The thermohaline characteristics of the Gulf of Aqaba, Red Sea, depict a welldefined seasonal pattern of winter mixing from December to April and summer stratification from May to November. This thermohaline structure is a major controlling factor of the nutrient, chlorophylla and primary productivity seasonal cycles. The nitrate and chlorophylla concentration records generated down to 200 m at a vertical resolution of 25 m – weekly during 1994, 1995 and every two weeks from April 1997 through to December 2000 – are employed to assess the nitrogen flux across the summer thermocline of the Gulf of Aqaba. The flux calculations are based on a simple diffusion model that incorporates the physical stress eddy diffusivity factor Kz and a biological stress factor k .B oth Kz and k are calculated using the Michaelis-Menten equation and the nitrate concentration gradient. The total nitrate flux of the Gulf of Aqaba during the seven summer months (May–November) is estimated at 0.52 mole N m −2 .I n relation to established primary productivity values (75.5 g C m −2 (May November) −1 )a nd The complete text of the paper is available at http://www.iopan.gda.pl/oceanologia/