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

Abstract

The uptake of anthropogenic CO₂ by the ocean is simulated using a perturbation approach in a three‐dimensional global general circulation model. Atmospheric pCO₂ is prescribed for the period 1750–1990 using the combined Siple ice core 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 (such as from deforestation, enhanced growth of land biota, and changes in the ocean carbon cycle) 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. Details of the penetration into different oceanic regions are discussed.