Seasonal and interannual CO2 fluxes for the central and eastern equatorial Pacific Ocean as determined from fCO2-SST relationships

Abstract

In order to determine high-resolution variations of CO2 distributions in the equatorial Pacific, we have developed seasonal and interannual fCO2-SST relationships from shipboard data. The data were gathered onboard NOAA ships from 1992 through 2001. The cruises during the 10-year period included 89 transects of the equatorial Pacific between 95°W and 165°E, and spanned two El Niño events (1992-1994 and 1997-1998). Data were collected during the equatorial warm season (January-June) and cool season (July-December as well as during all phases of the ENSO cycle, making it possible to examine the interannual and seasonal variability of the fCO2-SST relationship. There is a significant difference between the regression lines for El Niño versus non-El Niño data sets. During both non-El Niño and El Niño periods we observed seasonal differences in the fCO2-temperature relationship. With respect to the non-El Niño period, the seasonal regression lines have lower root mean square (rms) deviations than the composite non-El Niño regression line, and the slopes are significantly different at the 95% confidence level. The slope for the cool season is less negative than the slope for the warm season, suggesting higher biological productivity occurs during the latter half of the year. The derived fCO2-SST relationships have been combined with satellite-based temperature data to provide a composite time-space map of fCO2 in the central and eastern equatorial Pacific and corresponding fluxes for the period between 1985 and 2001. The mean flux for the 16-year record is 0.3 ± 0.1 PgC yr-1 for an area that covers approximately half of the Pacific equatorial belt.