Airborne observations of the tropospheric CO2 distribution and its controlling factors over the South Pacific Basin

Highly precise measurements of CO2 mixing ratios were recorded aboard both the NASA DC-8 and P3-B aircraft during the Pacific Exploratory Mission-Trop ics conducted in August-October 1996. Data were obtained at altitudes rangi ng from 0.1 to 12 km over a large portion of the South Pacific Basin repres enting the most geographically extensive CO2 data set recorded in this regi on. These data along with CO2 surface measurements from the National Oceani c and Atmospheric Administration/Climate Monitoring and Diagnostics Laborat ory (NOAA/CMDL) and the National Institute of Water and Atmospheric Researc h (NIWA) were examined to establish vertical and meridional gradients. The CO2 spatial distribution in the southern hemisphere appeared to be largely determined by interhemispheric transport as air masses with depleted CO2 le vels characteristic of northern hemispheric air were frequently observed so uth of the Intertropical Convergence Zone. However, regional processes also played a role in modulating background concentrations. Comparisons of CO2 with other trace gases indicated that CO2 values were influenced by contine ntal sources. Large scale plumes from biomass burning activities produced e nhanced CO2 mixing ratios within the lower to midtroposphere over portions of the remote Pacific. An apparent CO2 source was observed in the NOAA/ CMD L surface data between 15 degrees N and 15 degrees S and in the lower altit ude flight data between 8 degrees N and 8.5 degrees S with a zone of intens ity from 6.5 degrees N to 1 degrees S. Inferred from these data is the pres ence of a Southern Ocean sink from south of 15 degrees S having two distinc t zones seasonally out of phase with one another.