Evaluating Contributions of Wetland and Lake Emissions of Methane to Atmospheric Methane Concentrations with models of Biogeochemistry and Atmospheric Chemistry Transport in Northern High Latitudes

Northern high latitudes (north of 45oN) contain vast areas of wet tundra, wetlands, and water bodies (lakes and ponds), that are emitting a large amount of methane to the atmosphere each year. To date, the magnitudes and the inter-annual variations of these emissions are uncertain. The seasonal variations of these emissions due to changes of inundation of wetlands, the effects of spring thaw and winter freezing, and the effects of permafrost degradation in lands and lakes are also uncertain. In addition, how these emission dynamics affect the temporal and spatial distributions of atmospheric methane concentrations is not yet well understood. Here we use a process-based biogeochemistry model called TEM (the Terrestrial Ecosystem Model) to quantify these emissions with three different datasets for wetland and lake distributions. The effects of spring thaw and winter freezing on methane emissions are also incorporated into the TEM simulations. These estimated emissions together with wildfire emissions are then incorporated into a 3-D atmospheric chemistry transport model (GEOS-Chem) to simulate atmospheric methane concentration profiles. The satellite retrieval data of AIRS are then compared with the simulated methane concentration profiles for the region. We find that the current regional land and lake methane emissions range from 65 to 150 Tg per year. Seasonal changes of emissions of land and lakes due to spring thaw and winter freezing, together with fire emissions, play a significant role in determining the seasonal atmospheric methane concentration profiles simulated with GEOS-Chem. Comparison between multiple GEOS-Chem simulations driven with different seasonal dynamics of land, lake, and wildfire emissions and AIRS retrievals, suggests that accurately simulating the timing of these emissions as affected by spring thaw and winter freezing and wildfires, is critical for GEOS-Chem to capture the atmospheric concentration profiles over the region.