The theory of advective effects is extended to include localization effects, due both to the attenuation of light with depth in the ocean and to nutrient transport into the euphotic zone of finite duration in time and/or over a limited horizontal domain. Nutrient uptake is also generalized to nonlinear Michaelis–Menten kinetics. The characteristic curves are solved for explicitly, and a symbolic general solution is obtained for arbitrary biological dynamics. Some exemplary results are presented for the effect of light, nutrient, and grazing limitations on primary productivity in an NPZ–model. The theory is now applicable to further studies of more realistic oceanic processes.