Feely1, R.A., C.L. Sabine1, R. Wanninkhof2, W. McGillis3, M.-E. Carr4, C.E. Cosca1, M.F. Lamb1 and D. Greeley1

1Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115 USA, Phone: 206-526-6214; Fax: 206-526-6744, E-mail: Feely@pmel.noaa.gov, 2Atlantic Oceanographic and Meteorological Laboratory, National Oceanic and Atmospheric Administration, 4301 Rickenbacker Causeway, Miami, FL 33149 USA, 3Woods Hole Oceanographic Institution, Woods Hole, MA 05543 USA and 4Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA USA


CO2 mass balance and gas exchange during the GasEx-2001 experiment in the eastern equatorial Pacific


During the recent GasEx-2001 cruise in the equatorial Pacific aboard the NOAA Ship RONALD H. BROWN, carbon measurements were performed in the area of 3░S, 125░W. Continuous surface water fCO2 measurements were combined with vertical profiles sampled twice daily to depths up to 1000 m for carbon mass balance studies. Dissolved inorganic carbon (DIC) and fCO2 measurements were conducted onboard in both underway and discrete analysis modes. Over the 13-day study period, a DIC budget was constructed for the surface waters; the net drop in mixed layer DIC was 6.5 Ámol kg-1. The net precipitation resulted in a DIC decrease of 1.2 Ámol kg-1; entrainment of DIC from below the mixed layer decreased the net physical effect to 0.9 Ámol kg-1 (13.5%); biological new production removed 1.1 Ámol kg-1 (17.5%) of DIC; and air-sea gas exchange accounted for 69% (4.5 Ámol kg-1) of the total DIC removal from the mixed layer during this period. These results were combined with previous measurements collected on the Brown and Kaĺimimoana over the past ten years to obtain estimates of the regional CO2 flux between 5░N to 10░S, 90░W to 165░E. Using the McGillis et al. (2003) gas transfer-wind speed relationship, we observed a 20-fold difference in the regional efflux of CO2 between the strong El Ni˝o events of 1986-87 and 1997-98 and the La Ni˝a events of 1996 and 1999-2001 (i.e., 0.03 to 0.58 Pg C yr-1). The combined effects of uncertainties in the gas transfer velocity and wind fields lead to a maximum average difference of approximately 27 % in the overall estimate of the CO2 flux from the region.