A perturbation simulation of CO₂ uptake in an ocean general circulation model

Atmospheric pCO₂ is prescribed for the period 1750-1990 using the combined Siple ice cores and Mauna Loa records. For the period 1980 to 1989, the average flux of CO₂ into the ocean is 1.9 GtC/yr. However the bomb radiocarbon simulation of Toggweiler et al. (1989b) shows that the surface to deep ocean exchange in this model is too sluggish. Hence the CO₂ uptake calculated by the model is probably below the actual value. The observed atmospheric increase in 1980 to 1989 is 3.2 GtC/yr, for a combined atmosphere-ocean total of 5.1 GtC/yr. This is comparable to the estimated fossil CO₂ production of 5.4 GtC/yr, implying that other sources and sinks must be approximately in balance. The sensitivity of the uptake to the gas exchange rate is small: a 100% increase in gas exchange rate gives only a 9.2% increase in cumulative oceanic uptake. -from Authors