Carbon river fluxes and weathering CO2 consumption in the Congo and Amazon river basins

Data on carbon river fluxes recently obtained by the authors for the Congo basin within the framework of the PIRAT Program (INSU-CNRS/ORSTOM) are compared with results previously obtained for the Amazon basin. A special interest is devoted to the bicarbonate river fluxes and to their relationships with river discharges. The flux of atmospheric and soil CO₂ consumed by rock weathering is estimated to be 3.1 × 10⁵ and 0.5 × 10⁵ moles/a/km² respectively for the Amazon and the Congo basin. These CO₂ fluxes represent, respectively, 67.4% and 74.7% of the total bicarbonate river fluxes. A comparison to other large river basins shows that this contribution is directly related to the proportion of carbonate rock areas. A transfer function between the weathering CO₂ flux and the river discharge is calculated for each basin and allows the reconstitution of the variations of this flux using the river discharge fluctuations during the last century. These interannual CO₂ fluctuations present average increasing trends of 10% for Amazon basin and only 0.7% for the Congo basin during the last century.