Variation of CO2 partial pressure in surface seawater in the equatorial Pacific Ocean

The partial pressure of CO2 gas in surface seawater (pCO(2)(sea)) and in the atmosphere (pCO(2)(air)) was continually measured in the equatorial Pacific Ocean during two US JGOFS cruises in 1992. Time-series measurements at the equator and 140 degrees W show that the pCO(2) of surface seawater varied by 30 mu atm during the 2 week period of the experiment with a diurnal variation of close to 8 mu atm. The diurnal variations of pCO(2)(sea) were associated with the diurnal variations in sea surface water temperature, but the larger variation of pCO(2)(sea) on a weekly time-scale was associated with water movements (equatorial upwelling and passage of a tropical instability wave) rather than heating or cooling of surface seawater. The water movements are characterized by change in temperature as well as salinity, total inorganic carbon and total alkalinity. During the upwelling period, pCO(2)(sea) increased whereas sea surface temperature decreased. From the equator to 13 degrees S, pCO(2)(sea) decreased from 430 mu atm to 340 mu atm whereas the sea surface temperature increased from 25.4 degrees C to 28.3 degrees C. However, there was no overall correlation between pCO(2)(sea) and sea surface temperature. Indeed, the pCO(2)(sea) varied irregularly with temperature across a complex system of fronts and eddies. The observed diurnal variations of pCO(2)(sea) while the ship was in transit between Tahiti and the equator were up to 8 mu atm. (C) 1997 Elsevier Science Ltd.