EL-NINO-SOUTHERN OSCILLATION RELATED FLUCTUATIONS OF THE MARINE CARBON-CYCLE

We investigate the response of a three-dimensional ocean circulation model (Hamburg LSG) coupled on-line with an oceanic carbon cycle model (HAMMOCC-3) to El Nino-Southern Oscillation (ENSO) induced fluctuations of the wind field. During El Nino 1982/1983, when upwelling and biological productivity in the equatorial Pacific were strongly reduced and sea surface temperatures were increased, the oceanic CO2 partial pressure in this region decreased significantly. Consequently, in 1982/1983 the CO2 flux from the tropical ocean into the atmosphere was reduced. However, in 1983 the interannual deviations from the long-term trend in atmospheric CO2 showed in January low and in December high values with a total shift by more that 1.4 GtC. The model simulation support the oceanic measurements and predicts a temporary uptake of 0.6 GtC during the ENSO year 1983. We conclude that the concurrent release of CO2 from the land biosphere must have been about 2 GtC.