Short-term changes in the partial pressure of CO(2) in eastern tropical Atlantic surface seawater and in atmospheric CO(2) mole fraction

Continuous monitoring of oceanic and atmospheric CO(2) during periods of 8 to 12 days in two particular locations of the tropical Atlantic was carried out during June-August 1986. At the first location (convergence zone; about 5 degrees N, 20 degrees W), the ocean surface was generally slightly undersaturated with respect to the atmosphere, whereas at the second one (Guinea Dome; 12 degrees N, 22 degrees W), the ocean surface was an important source zone of CO(2) for the atmosphere. The results of PCO(2) in surface seawater, after correction of the temperature effect, show a decrease between morning and evening related to photosynthetic activity. Over a 3-day period, the CO(2) concentration in the air above the Ocean may vary up to +/- 0.6 ppm d(-1) at the same location, whereas the wind direction hardly changes. The net CO(2) flux changes considerably during a short period (8 to 12 days) in the same place, as does the gas transfer coefficient across the sea surface through the variation of the wind speed: the variability is about 80-90%. The net CO(2) flux calculated from mean data is lower (about 30%) than the net CO(2) flux calculated from data taken over short time intervals. In the Guinea Dome area in summer, the net CO(2) flux can be as high (1.8 mmol m(-2) d(-1)) as in the equatorial area.