Using phytoplankton pigments as biomarkers, we investigated the relationship between the physical forcing and the resulting biological, ecological and biogeochemical properties of the geostrophic front of the Eastern Alboran Sea. (1) Typical frontal sites present biomass levels averaging 60 mg chl a m−2 (up to 100 mg m−2), whereas the adjacent zones (typical Atlantic and Mediterranean) are characterized by an average integrated chlorophyll biomass of 20 mg chl a m−2. (2) The phytoplankton biomass at front is diatom-dominated and differs markedly from the adjacent zones (typical Atlantic and Mediterranean), flagellate- and cyanobacteria-dominated. Therefore, high biomasses at the front do not result from purely physical accumulation but rather from local production. (3) The chlorophyll and diatom biomasses increase from the left to the right side of the Atlantic jet, which supports the hypothesis of a cross-frontal secondary circulation allowing a diatom bloom development. (4) Using assumptions on the carbon/chlorophyll ratio and growth rates for the different phytoplankton taxa, we evaluated the specific productions: diatoms account for 67% of the production at front and only about 10% at adjacent zones. (5) High concentrations of phaeopigments are only found at frontal stations, which points out the pecularities of the food web at the frontal site, compared to adjacent areas. (6) The observations made during this study give a precise picture of that frontal system: autotrophic new production and exportation are enhanced. The implication of this frontal system on the carbon budget at a regional scale may be important.