Current coupled ocean-atmosphere model (COAM) projections of future oceanic anthropogenic carbon uptake suggest reduced rates due to surface warming, enhanced stratification, and slowed thermohaline overturning. Such models rely on simple, bulk biogeochemical parameterisations, whereas recent ocean observations indicate that floristic shifts may be induced by climate variability, are widespread, complex, and directly impact biogeochemical cycles. We present a strategy to incorporate ecosystem function in COAM's and to evaluate the results in relation to region-specific ecosystem dynamics and interannual variability using a template of oceanic biogeographical provinces. Illustrative simulations for nitrogen fixers with an off-line multi-species, functional group model suggest significant changes by the end of this century in ecosystem structure, with some of the largest regional impacts caused by shifts in the areal extent of biomes.