Distribution of chemical tracers in the eastern equatorial Pacific during and after the 1982–1983 El Niño/Southern Oscillation event

Abstract

During April 1983 and March‐April 1984, two cruises were conducted in the central equatorial Pacific to determine the effects of the El Niño/Southern Oscillation (ENSO) event on the sea‐air exchange of CO 2 . Measurements of total carbon dioxide, p CO 2 , total alkalinity, freon‐11, salinity, temperature, oxygen, nutrients, and wind and current velocities were made along three meridional transects (158°W, April 1983; 150°W, March 1984; 170°W, April 1984). The cessation of upwelling during the ENSO event caused p CO 2 concentrations in surface waters to decrease to near‐saturation levels along the equator. The calculated net flux of CO 2 across the sea‐air interface was essentially negligible in the eastern equatorial Pacific during this period. However, when normal trade winds and consequent upwelling returned in late 1983 and early 1984, the equatorial region returned to a p CO 2 condition of highly supersaturated surface waters in the region between 8°N and 8°S along the 150° and 170°W transects. The calculated post‐ENSO sea‐air flux of CO 2 exceeded 6.0 mmol CO 2 m −2 d −1 The mean annual CO 2 flux in the equatorial Pacific was estimated to be 0.02 Gt of carbon during the 1982–1983 ENSO event as compared with 0.6 Gt during 1984.