Absorption et régénération de l'azote dans la zone frontale du courant Algérien (Méditerranée Occidentale) : réévaluation de la production nouvelle

The uptake and regeneration of four forms of nitrogen NO3-, NO2-, NH4+ and urea) have been studied, in the euphotic layer of a frontal area (Algerian current), in relation with hydrological, chemical and biological parameters. Ln this area vertical stratification is pronounced; a deep chlorophyll maximum at the bottom of the euphotic layer is present. Results show the importance of measuring urea uptake and regeneration in the study of nitrogen cycling, because this component can be regenerated as rapidly as ammonia, and is a source of nitrogen for phytoplankton. Other results show the oxidation of ammonia to nitrate in the euphotic layer, and particularly at the base of this layer. This nitrification is a source of in situ regenerated nitrate, and could lead to a wrong estimation of the new production estimation.