Amazon Column CO2 & CO Observations to Elucidate Tropical Ecosystem Processes
Friday, 18 December 2015: 11:35
3006 (Moscone West)
The Amazon basin stores 150-200 PgC, exchanges 18 PgC with the atmosphere every year and has taken up 0.42-0.65 PgC/y over the past two decades. Despite its global significance, the response of the tropical carbon cycle to climate variability and change is ill constrained. The complex interplay of radiation, water and ecosystem phenology remains unresolved in tropical ecosystem models. We use high frequency regional scale TCCON observations of column CO2, CO and CH4 near Manaus, Brazil that began in October 2014 to understand the aforementioned interplay of processes. We observe a robust mean daily column CO2 uptake of about 1.8 ppm (5 ppm to 0.5 ppm) over 8 hours and evaluate how it changes as we transition to the dry season. Back-trajectory calculations show that the daily CO2 uptake footprint is terrestrial and influenced by the heterogeneity of the Amazon rain forests. The column CO falls from above 120 ppb to below 80 ppb as we transition from the biomass burning to wet seasons. The daily mean column CO2 rises by 3 ppm from October through June. Removal of biomass burning and secular CO2 increase during this period implies an increase of 3.5 ppm that is attributed to tropical biospheric processes (respiration and photosynthesis). This is consistent with ground-based and eddy flux observations that indicate that tree phenology (e.g. leaf flushing) plays an important role in the tropical carbon cycle in regions that are not water limited and is not considered in current models. We compare our observations with output from carbon cycle models with assimilated meteorology (e.g. NASA’s CASA/GFED) and find they under predict the daily drawdown of CO2 by a factor of 2.5. We plan to perform comparisons with other models (e.g. CLM) and also determine the net carbon flux from the Amazon basin by combining back-trajectory analysis and observations of column CO2 made at Ascension Island that is upwind of our site.