Data on the rate of primary production, the rate of sinking and oxidation of organic detritus, the rate of regeneration of calcium carbonate, the average rate of vertical mixing, and the vertical profile of dissolved carbon are consistent with a model of the ocean in which the downward transport of carbon by the sinking and oxidation of organic particulate matter is balanced by upward hydrodynamic mixing of dissolved inorganic carbon. A time dependent version of this model is used to make rough estimates of the effect of periodic and impulsive changes in the rate of primary production on the atmospheric CO2 concentration. The computations suggest that a 1% decrease in marine biospheric productivity could result in a steady state increase of the atmospheric CO2 concentration of from 0.5 to 2.5% depending on the rate of vertical mixing. Large but short term fluctuations in productivity, such as a die-off of the marine biosphere followed by an exponential recovery period, are estimated to produce smaller perturbations. k Eddy mixing coefficient C Inorganic carbon concentration C O Surface carbon concentration Cp Rate of primary production CBW Rate of bottom water formation z Depth d Bottom of the ocean ~6000 m W Vertical upwelling velocity Radian frequency Pa Atmosphere CO 2 concentration v m Mixed layer carbon concentration kam Atmosphere-mixed layer exchange rate ~ 1]7.3 yr -1 kma Mixed layer-atmosphere exchange rate ~ 1/10 yr -1 Buffer factor ~ 10 h m Mixed layer depth ~ 75 m C d Average ocean carbon concentration ~ 2.3 tool m-3 3' Carbon concentration below the mixed layer o~ Reciprocal of atmospheric response time constant Reciprocal of productivity recovery time constant Po Ampfitude of atmospheric response