An optimization experiment is performed with avertically resolved, nitrogen based ecosystem model, comprising fourstate variables (NPZD-model): dissolved inorganic nitrogen (N),phytoplankton (P), herbivorous zooplankton (Z) and detritus (D).Parameter values of the NPZD-model are optimized by assimilatingobservations at three locations in the North Atlantic simultaneously,namely at the station of the Bermuda Atlantic Time-series Study(BATS; 32N 64W), at the site of the North AtlanticBloom Experiment (NABE; 47N 20W) and at the position of theOcean Weather Ship-India (OWS-INDIA; 59N 19W).A method is described for simultaneous optimization which effectivelymerges different types of observational data at distinct sites in the ocean. Amicro-genetic algorithm is applied for the minimization of a weighted leastsquare misfit function. The simultaneous optimization yields a bestparameter set which can be adopted for basin wide simulations incoupled physical-biological for basin wide simulations in coupledphysical-biological (general circulation) models of the North Atlantic.The optimal parameter estimates are shown to representa compromise among local parameter estimates obtained fromsingle-site optimizations at the individual locations.The optimized parameter set is compared with a set of traditionallypublished values. Drastic changes due to the optimization canbe attributed to the estimates of the initial slope parameter ofthe light limited growth function ($\alpha$) and to the recyclingof organic nitrogen. High estimates of $\alpha$ arewell constrained by chlorophyll observations at the BATS andOWS-INDIA sites, in order to match initial bloom phases.The optimization points towards rapid remineralization processes,expressed in high optimal estimates for the phytoplanktonmortality/excretion rate, which is necessary forthe model to achieve a better agreement with primaryproduction measurements.