GAINING INSIGHT INTO THE SEASONAL VARIABILITY OF CO2 AT OCEAN STATION-P USING AN UPPER OCEAN MODEL

An eddy-kinetic energy model for simulations of the oceanic vertical mixing (GASPAR et al., 1990, Journal of Geophysical Research, 95, 16179-16193) is used to investigate the seasonal cycle of dissolved total CO2 and CO2 partial pressure at Station P (Gulf of Alaska) during the years 1971 and 1972. The model simulates relatively weak seasonal variations of surface seawater pCO2. All processes appear to contribute to the same order of magnitude: interaction of gas exchange and biology tends to compensate for the thermodynamical effect on pCO2. The influence of various model parameters (total annual production of O2, P, depth of photic zone, z0, gas transfer velocity, K) on the seasonal variability of seawater PCO2 and air-Sea CO2 flux is examined. Total annual production, P, seems to be the most influential. The model also suggests a strong short-term variability of PCO2 during episodic events. Model results show that the area around Station P behaves as a weak or neutral CO2 source during summer and as a net sink during other seasons. The net annual CO2 flux is an invasion flux, with values of 0.88 and 0.70 mol m-2 y-1 for 1971 and 1972, respectively, in agreement with the flux of 0.7 mol m-2 y-1 derived from observations during 1973-1978 (WONG and CHAN, 1991, Tellus, 43B, 206-223).