Effects of wind speed and gas exchange parameterizations on the air-sea CO2 fluxes in the equatorial Pacific Ocean

Abstract

During the recent GasEx-2001 cruise in the Equatorial Pacific aboard the NOAA ship Ronald H. Brown, carbon measurements were made in the region of 3°S, 125°W. Continuous surface water fCO2 measurements were conducted onboard in both underway and discrete analysis modes. During the 15-day experiment, surface water fCO 2 values averaged 473 ± 2 μatm, providing a constant condition of supersaturation and flux of CO2 from the ocean to the atmosphere. The relationship of gas transfer with wind speed developed in this study is used along with regional estimates of air-water fCO2 differences to determine CO2 fluxes in the equatorial Pacific. The regional fCO2 fields are estimated from algorithms developed from previous measurements collected on the Ronald H. Brown and Ka'imimoana over the past 10 years between 5°N and 10°S, 90°W and 165°E. Using the W. McGillis et al. gas transfer-wind speed relationship, we estimate an average flux of 1.5 ± 0.4 mol C m-2 yr-1 for the study region, with a six-fold difference in the regional efflux of CO 2 between the strong El Niño events of 1986-1987 and 1997-1998 and the La Niña events of 1996 and 1999-2001 (i.e., 0.1 to 0.56 Pg C yr-1). The combined effects of uncertainties in the gas transfer velocity and wind fields lead to average difference of 27% between the lowest and highest estimates of the CO2 flux from the region. In contrast, the uncertainties in the fCO 2-SST relationships give an average difference of about 35% between the lowest and highest estimates of the CO2 flux. Copyright 2004 by the American Geophysical Union.