During a SOP cruise (Special Observation Period) of the GARP program, a 14 days station was occupied in the equatorial Atlantic Ocean (0⁰-4⁰ W). Vertical oscillation of the hydrological structure (thermocline, nifracline, nitrite maximum) was observed according to the south-north oscillations of fhe equatorial current system (surface current and undercurrent). Chlorophyll distribution and primary production values are greatly influenced by these oscillations. From our data, it seems that the tore of the Lomonosov current is the most productive pari of the equatorial area. An “Ecological Equator”, (between 0⁰ 30 S and 0⁰ 30 N) is introduced; in this area, the primary production changes from 1 to 2 g C m^-2 d^-l in few days with a constant solar radiation (Total irradiante: 2100 J cm^-2 d^l-).