IN the midst of the debate over the ocean being phosphorus- or nitrogen-limited1,2, the 'acid rain' controversy prompted studies related to the atmospheric transport and delivery of pollutant nitrogen compounds over the ocean3-9. Some of those investigations concluded that atmospheric nitrogen had only minimal effects on euphotic-zone productivity7,8 or on nitrate at the Atlantic thermocline9, thus suggesting a negligible oceanic role for pollutant atmospheric nitrogen. Here I give evidence to the contrary, by clearly showing that, whereas nitrogen limitation is much more prevalent than phosphorus limitation in the surface ocean, those areas with the strongest indications of phosphorus limitation in the North Atlantic and North Pacific are downwind of the most populated and urbanized regions of eastern Asia and North America. This geographic coincidence and the timing and composition of atmospheric nitrogen deposition suggest a plausible, albeit untested, mechanism whereby airborne pollutant nitrogen can lead to phosphorus limitation.