New production and the global carbon cycle

The export of newly produced organic carbon from the surface ocean and its regeneration at depth account for an estimated three-quarters of the vertical ΣCO2 gradient shown in Fig. 1 (Volk and Hoffert, 1985). If these processes, often referred to as the “biological pump,” had ceased operating during the pre-industrial era, the increase in surface ΣCO2 resulting from upward mixing of high ΣCO2 deep waters would have raised atmospheric pCO2 from 280 ppm to the order of 450 ppm (Sarmiento and Toggweiler, 1984) over a period of centuries. Vertical exchange, which gives an estimated upward flux of 100 GtC/yr (Fig. 2), works continuously to bring about just such a scenario. The biological pump prevents it by stripping out about 10 GtC/yr, so that the water arriving at the surface has a concentration equal to that which is already there.