Vertical profiles of CO₂ above eastern Amazonia suggest a net carbon flux to the atmosphere and balanced biosphere between 2000 and 2009

Abstract

From 2000 until January 2010 vertical profiles were collected above eastern Amazonia to help determine regional-scale (¡«105¨C10⁶ km²) fluxes of carbon cycle-related greenhouse gases. Samples were collected aboard light aircraft between the surface and 4.3 km and a column integration technique was used to determine the CO₂ flux. Measured CO₂ profiles were differenced from the CO₂ background determined from measurements in the tropical Atlantic. The observed annual flux between the coast and measurement sites was 0.40 ¡À 0.27 gC m^-2 d^-1 (90% confidence interval using a bootstrap analysis). The wet season (January¨CJune) mean flux was 0.44 ¡À 0.38 gC m^-2 d^-1 (positive fluxes defined as a source to the atmosphere) and the dry season mean flux was 0.35 ¡À 0.17 gC m^-2 d^-1 (July¨CDecember). The observed flux variability is high, principally in the wet season. The influence of biomass burning has been removed using co-measured CO, and revealed the presence of a significant dry season sink. The annual mean vegetation flux, after the biomass burning correction, was 0.02 ¡À 0.27 gC m^-2 d^-1, and a clear sink was observed between August and November of -0.70 ¡À 0.21 gC m^-2 d^-1 where for all of the dry season it was -0.24 ¡À 0.17 gC m^-2 d^-1.