No abstract

From 2000 until January 2010 vertical profiles were collected above eastern Amazonia to help determine regional‐scale (∼105–106 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 ± 0.27 gC m−2 d−1 (90% confidence interval using a bootstrap analysis). The wet season (January–June) mean flux was 0.44 ± 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 ± 0.17 gC m−2 d−1 (July–December). 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 ± 0.27 gC m−2 d−1, and a clear sink was observed between August and November of −0.70 ± 0.21 gC m−2 d−1 where for all of the dry season it was −0.24 ± 0.17 gC m−2 d−1.

Abstract. Measurements of CH 4 mixing ratio, vertical gradients and turbulent fluxes were carried out in a tropical forest (Reserva Biológica Cuieiras), about 60 km north of Manaus, Brazil. The methane mixing ratio and flux measurements were performed at a height of 53 m (canopy height 35 m). In addition, vertical CH 4 gradients were measured within the canopy using custom made air samplers at levels of 2, 16 and 36 m above ground. The methane gradients within the canopy reveal that there is a continuous methane source at the surface. No clear evidence for aerobic methane emission from the canopy was found. The methane fluxes above the canopy are small but consistently upwards with a maximum early in the morning. The measured fluxes are in agreement with the observed CH 4 gradient in the canopy. In the morning hours, a strong canopy venting peak is observed for both CH 4 and CO 2 , but for CO 2 this peak is then superimposed by photosynthetic uptake, whereas the peak lasts longer for CH 4 . Monthly averaged diurnal cycles of the CH 4 mixing ratio show a decrease during daytime and increase during nighttime. The magnitude of the difference in CH 4 mixing ratio between day and night gradually increases throughout the wet season. The fluxes required to explain the nighttime increase are in agreement with the nighttime fluxes measured above the canopy, which implies that the CH 4 increase in the nighttime boundary layer originates from local sources.

Measurements of CH₄ mixing ratio, vertical gradients and turbulent fluxes were carried out in a tropical forest (Reserva Biológica Cuieiras), about 60 km north of Manaus, Brazil. The methane mixing ratio and flux measurements were performed at a height of 53 m (canopy height 35 m). In addition, vertical CH₄ gradients were measured within the canopy using custom made air samplers at levels of 2, 16 and 36 m above ground. The methane gradients within the canopy reveal that there is a continuous methane source at the surface. No clear evidence for aerobic methane emission from the canopy was found. The methane fluxes above the canopy are small but consistently show an upward flux with a maximum early in the morning, and the measured fluxes are in agreement with what is expected from the positive CH₄ gradient in the canopy. In the morning hours, a strong canopy venting peak is observed for both CH₄ and CO₂, but for CO₂ this peak is then superimposed by photosynthetic uptake, whereas the peak lasts longer for CH₄. Monthly averaged diurnal cycles of the CH₄ mixing ratio show a decrease during daytime and increase during nighttime. The magnitude of the difference in CH₄ mixing ratio between day and night gradually increases throughout the wet season. The fluxes required to explain the nighttime increase are in agreement with the nighttime fluxes measured above the canopy, which implies that the CH₄ increase in the nighttime boundary layer originates from local sources