Variability in terrestrial carbon sinks over two decades. Part III: South America, Africa, and Asia

Seventeen years (1982-98) of net carbon flux predictions for Southern Hemisphere continents have been analyzed, based on a simulation model using satellite observations of monthly vegetation cover. The NASA Carnegie Ames Stanford Approach (CASA) model was driven by vegetationcover properties derived from the Advanced Very High Resolution Radiometer and radiative transfer algorithms that were developed for the Moderate Resolution Imaging Spectroradiometer (MODIS). The terrestrial ecosystem flux for atmospheric CO₂ for the Amazon region of South America has been predicted between a biosphere source of -0.17 Pg C per year (in 1983) and a biosphere sink of +0.64 Pg C per year (in 1989). The areas of highest variability in net ecosystem production (NEP) fluxes across all of South America were detected in the south-central rain forest areas of the Amazon basin and in southeastern Brazil. Similar levels of variability were recorded across central forested portions of Africa and in the southern horn of East Africa, throughout Indonesia, and in eastern Australia. It is hypothesized that periodic droughts and wildfires associated with four major El Niño events during the 1980s and 1990s have held the net ecosystem carbon sink for atmospheric CO₂ in an oscillating pattern of a 4-6-yr cycle, despite observations of increasing net plant carbon fixation over the entire 17-yr time period.