AN ESTIMATE OF CO2 FLUX IN LAKE NYOS, CAMEROON

An outburst of lethal gas from Lake Nyos, Cameroon, killed more than 1 ,700 people on 21 August 1986. The surveys carried out so far indicate that a considerable portion of the CO, dissolved in the lake was rele ased to the atmosphere and asphyxiated the people. We revisited the la ke in December 1988. The conductivity-temperature-depth profiler (CTD) measurements and chemical analysis of the lake water revealed that te mperature, total dissolved solids (TDS), and CO2 content of the bottom water increased in parallel fashion, especially in the bottom layer, during the preceding 25 months. The result supports the view that CO2 is being supplied to the lake bottom in the form of warm, CO2-charged, mineralized water. From the increments of temperature and CO2 during the period, fluxes of heat and CO2 were estimated to be 0.43 MW and 1. 0 Mmol yr-1. The CO2 flux is large enough to saturate the lake's hypol imnion within approximately 30 yr. In the 1988 survey, the very bottom layer of the lake was estimated to be close to saturation with CO2. U sing the CO2-TDS-Si relationship and temperature dependence of the sol ubility of amorphous silica, we estimated the chemical composition of the warm, mineralized water; these estimates suggest the existence of a CO2-saturated fluid below the sedimentary cover.