Fig. 1.

Salient features of global four-box model with fixed (A) vs. variable (B) stoichiometry. Thermohaline circulation (black arrows) creates an overall ocean circulation from low to high latitudes to deep water and back to low latitudes, which partially accounts for the movement of carbon (red) and phosphorus (blue). However, carbon exchanges with the atmosphere and both C and P sink into deep water at both high and low latitudes. Total C and P inventories are considered fixed at this time scale. The effect of allowing for variable stoichiometry is to increase the C:P ratio (decrease the P:C) of particles at low latitudes, which at steady state redistributes carbon from the atmosphere into the deep ocean.