Satellite sea surface temperature: a powerful tool for interpreting in situ pCO(2) measurements in the equatorial Pacific Ocean

In order to determine the seasonal and interannual variability of the CO2 r eleased to the atmosphere from the equatorial Pacific, we have developed pC O(2)-temperature relationships based upon shipboard oceanic CO2 partial pre ssure measurements, pCO(2), and satellite sea surface temperature, SST, mea surements. We interpret the spatial variability in pCO(2) with the help of the SST imagery. In the eastern equatorial Pacific, at 5 degrees S, pCO(2) variations of up to 100 mu atm are caused by undulations in the southern bo undary of the equatorial upwelled waters. These undulations appear to be pe riodic with a phase and a wavelength comparable to tropical instability wav es, TIW, observed at the northern boundary of the equatorial upwelling. Onc e the pCO(2) signature of the TIW is removed from the Alize II cruise measu rements in January 1991, the equatorial pCO(2) data exhibit a diel cycle of about 10 mu atm with maximum values occurring at night. In the western equ atorial Pacific the variability in pCO(2) is primarily governed by the disp lacement of the boundary between warm pool waters, where air-sea CO2 fluxes are weak, and equatorial upwelled waters which release high CO2 fluxes to the atmosphere. We detect this boundary using satellite SST maps. East of t he warm pool, Delta P is related to SST and SST anomalies. The 1985-1997 CO 2 flux is computed in a 5 degrees wide latitudinal band as a combination of Delta P and CO2 exchange coefficient, K, deduced from satellite wind speed s, U. It exhibits up to a factor 2 seasonal variation caused by K-seasonal variation and a large interannual variability, a factor 5 variation between 1987 and 1988. The interannual variability is primarily driven by displace ments of the warm pool that makes the surface area of the outgassing region variable The contribution of Delta P to the flux variability is about half the contribution of K. The mean CO2 flux computed using either the Liss an d Merlivat (1986) or the Wanninkhof (1992) K-U parametrization amounts to 0 .11 GtC yr(-1) or to 0.18 GtC yr(-1), respectively. The error in the integr ated flux, without taking into account the uncertainty on the K-U parametri zation, is less than 31%.