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2 Oceanologia

2 2005

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Stratification of particulate organic carbon and nitrogen in the Gdańsk Deep (southern Baltic Sea)

Burska D., Pryputniewicz D., Falkowska L.

Oceanologia

2005

No. 47 (2)

201-217

Particulate organic carbon (POC) and nitrogen (PON) concentrations and fluxes were measured during an experiment in the Gdańsk Deep in late spring (30.05.-06.06.2001). The vertical POC and PON concentration profiles were characterised by the highest values in the euphotic layer, a gradual decrease with depth, and an increase below the halocline. The hydrophysical conditions had a decisive impact on POC and PON fluxes in the water column. Preferential removal of nitrogen from suspended mater was observed in the entire water column (maximum - in the vicinity of thermocline). There were also differences in the diurnal effectiveness of nitrogen removal as compared to carbon removal. The removal rate was highest at night.

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

Badran M. I., Rasheed M., Manasrah R., Al-Najjar T.

Oceanologia

2005

No. 47 (1)

47-60

The thermohaline characteristics of the Gulf of Aqaba, Red Sea, depict a well-defined 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, chlorophyll a and primary productivity seasonal cycles. The nitrate and chlorophyll a 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. Both 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. In relation to established primary productivity values (75.5 g C m-2 (May November)-1) and the generated chlorophyll a records, this yields an f fraction of new to total primary production of 0.50. This relatively high f value is discussed with respect to the geophysical characteristics of the Gulf of Aqaba and similar oceanic basins. The remaining 50% is accounted for by cross-sectional flow from the relatively nutrient-rich coral reef coastal habitat and rapid recycling, triggered by high irradiance and water temperature.