A simplified, two-layer, bio-physical model reveals regional regimes of biological response to interannual variability in convective mixing in the North Atlantic. The regimes may identified by the ratio of the thickness of Sverdrup's critical layer during spring and the end of winter mixed layer, hc/hm. The simplified model predicts that in subtropical regimes (hc/hm ~ 1), anomalously enhanced spring-time mixing will have a signature of enhanced surface chlorophyll. In subpolar regimes (hc/hm < < 1) anomalously enhanced spring-time mixing leads to reduced surface chlorophyll, with a much weaker dependence on mixing rate. The regimes predicted by the simplified model are found in a more sophisticated four-compartment, nitrogen based ecosystem model, driven by a general circulation model of the North Atlantic. The circulation model is forced with twelve-hourly surface fluxes from reanalysed meteorological data and we examine the period from 1987 to 1995. The numerical model also reveals regions of more complex behaviour, such as the inter-gyre boundary, where advective supply of nutrients plays a significant role on interannual timescales. Preliminary analyses of in situ and remote observations from the Bermuda Atlantic Time-Series, Ocean Weather Ship India and the Coastal Zone Color Scanner also show qualitative agreement. The conceptual framework provides a tool for the analysis of ongoing remote ocean color observations.