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

Author(s): Mohammad I. Badran | Mohammad Rasheed | Riyad Manasrah | Tariq Al-Najjar

Journal: Oceanologia
ISSN 0078-3234

Volume: 47;
Issue: 1;
Start page: 47;
Date: 2005;
Original page

Keywords: Diffusion model | Eddy diffusivity | Biological stress | Chlorophyll a | Thermohaline stratification

The thermohaline characteristics of the Gulf of Aqaba, Red Sea,depict a well-defined seasonal pattern of winter mixing from December toApril and summer stratification from May to November. This thermohalinestructure is a major controlling factor of the nutrient, chlorophyll aand primary productivity seasonal cycles. The nitrate and chlorophyll aconcentration records generated down to 200 m at a vertical resolution of25 m - weekly during 1994, 1995 and every two weeks from April 1997 throughto December 2000 - are employed to assess the nitrogen flux across the summerthermocline of the Gulf of Aqaba. The flux calculations are based on a simplediffusion model that incorporates the physical stress eddy diffusivity factorKz and a biological stress factor k. Both Kz and k arecalculated using the Michaelis-Menten equation and the nitrate concentrationgradient. The total nitrate flux of the Gulf of Aqaba during the seven summermonths (May-November) is estimated at 0.52 mole N m-2. In relation toestablished primary productivity values (75.5 g C m-2 (MayNovember)-1) and the generated chlorophyll a records, thisyields an f fraction of new to total primary production of 0.50. Thisrelatively high f value is discussed with respect to the geophysicalcharacteristics of the Gulf of Aqaba and similar oceanic basins. The remaining50% is accounted for by cross-sectional flow from the relativelynutrient-rich coral reef coastal habitat and rapid recycling, triggered byhigh irradiance and water temperature.
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