Seasonal Variability of Tropical Wetland CH4 emissions: the role of the methanogen-available carbon pool.

We develop a dynamic methanogen-available carbon model (DMCM) to quantify the role of the methanogen-available carbon pool in determining the spatial and temporal variability of tropical wetland CH₄ emissions over seasonal timescales. We fit DMCM parameters to satellite observations of CH₄ columns from SCIAMACHY CH₄ and equivalent water height (EWH) from GRACE. Over the Amazon river basin we find substantial seasonal variability of this carbon pool (coefficient of variation=28±22 %) and a rapid decay constant (φ= 0.017 day^-1), in agreement with available laboratory measurements, suggesting that plant litter is likely the prominent methanogen car bon source over this region. Using the DMCM we derive global CH₄ emissions for 2003-2009, and determine the resulting seasonal variability of atmospheric CH₄ on a global scale using the GEOS-Chem atmospheric chemistry and transport model. First, we estimate tropical emissions amount to 111.1 TgCH₄ yr^-1 of which 24% is emitted from Amazon wetlands. We estimate that annual tropical wetland emissions have in creased by 3.4 TgCH₄ yr^-1 between 2003 and 2009. Second, we find that the model is able to reproduce the observed seasonal lag between CH₄ concentrations peaking 1-3 months before peak EWH values. We also find that our estimates of CH₄ emissions substantially improve the comparison between the model and observed CH₄ surface concentrations (r = 0.9). We anticipate that these new insights from the DMCM represent a fundamental step in parameterising tropical wetland CH₄ emissions and quantifying the seasonal variability and future trends of tropical CH₄ emissions. [ABSTRACT FROM AUTHOR]