Decadal variability of the air‐sea CO₂ fluxes in the equatorial Pacific Ocean

Abstract

In order to determine the interannual and decadal changes in the air‐sea carbon fluxes of the equatorial Pacific, we developed seasonal and interannual relationships between the fugacity of CO 2 ( f CO 2 ) and sea surface temperature (SST) from shipboard data that were applied to high‐resolution temperature fields deduced from satellite data to obtain high‐resolution large‐scale estimates of the regional fluxes. The data were gathered on board research ships from November 1981 through June 2004 between 95°W and 165°E. The distribution of f CO 2sw during five El Niño periods and four La Niña periods were documented. Observations made during the warm boreal winter‐spring season and during the cooler boreal summer‐fall season of each year enabled us to examine the interannual and seasonal variability of the f CO 2sw ‐SST relationships. A linear fit through all of the data sets yields an inverse correlation between SST and f CO 2sw , with both interannual and seasonal differences in slope. On average, the surface water f CO 2 in the equatorial region has been increasing at a rate similar to the atmospheric CO 2 increase. In addition, there appears to be a slight increase (∼27%) in the outgassing flux of CO 2 after the 1997–1998 Pacific Decadal Oscillation (PDO) regime shift. Most of this flux increase is due to increase in wind speeds after the spring of 1998, although increases in f CO 2sw after 1998 are also important. These increases are coincident with the recent rebound of the shallow water meridional overturning circulation in the tropical and subtropical Pacific after the regime shift.