FY 1995

CO₂ distributions in the equatorial Pacific during the 1991–1992 ENSO event

Feely, R.A., R. Wanninkhof, C.E. Cosca, P.P. Murphy, M.F. Lamb, and M.D. Steckley

Deep-Sea Res. II, 42(2–3), 365–386, doi: 10.1016/0967-0645(95)00027-N (1995)

As part of the U.S. JGOFS Equatorial Pacific Process Study, measurements of CO₂ species concentrations were made in the atmosphere and in the surface waters of the central and eastern equatorial Pacific during the boreal spring and autumn of 1992. Surface water fCO₂ data indicate significant differences between the springtime El Niño conditions and the autumn post-El Niño conditions. The autumn fugacity (ΔfCO₂) maxima were approximately 15-55 µatm higher than in the spring. The lower surface ΔfCO₂ values in the spring data set were the result of: (i) advection of CO₂-depleted water from the west at the equator near 170°W; and (ii) reduced upwelling and lower ΔfCO₂ distributions as consequence of lighter zonal winds in the eastern Pacific from 140°W to 110°W. Assuming the springtime data are representative of the El Niño conditions and the autumn data are representative of the post-El Niño conditions, it is estimated that the net annual CO₂ flux during the 1991-92 ENSO period to be 0.3 Gt C. Over 60% of this flux occurred during the 4-month period in the autumn when ΔfCO2 values were close to normal. The net annual reduction of the ocean-atmosphere CO₂> flux during the 1991-92 El Niño is estimated to be on the order of 0.5-0.7 Gt C.