Mathematical Modelling of Arctic Polygonal Tundra with Ecosys:2. Microtopography Determines How CO2and CH4Exchange Responds to Changes in Temperature and Precipitation

Differences of surface elevation in arctic polygonal landforms cause spatial variation in soil water contents (θ), active layer depths (ALD), and thereby in CO2and CH4exchange. Here we test hypotheses in ecosysfor topographic controls on CO2and CH4exchange in trough, rim, and center features of low‐ and flat‐centered polygons (LCP and FCP) against chamber and eddy covariance (EC) measurements during 2013 at Barrow, Alaska. Larger CO2influxes and CH4effluxes were measured with chambers and modeled with ecosysin LCPs than in FCPs and in lower features (troughs) than in higher (rims) within LCPs and FCPs. Spatially aggregated CO2and CH4fluxes from ecosyswere significantly correlated with EC flux measurements. Lower features were modeled as C sinks (52–56 g C m−2yr−1) and CH4sources (4–6 g C m−2yr−1), and higher features as near C neutral (−2–15 g C m−2yr−1) and CH4neutral (0.0–0.1 g C m−2yr−1). Much of the spatial and temporal variations in CO2and CH4fluxes were modeled from topographic effects on water and snow movement and thereby on θ, ALD, and soil O2concentrations. Model results forced with meteorological data from 1981 to 2015 indicated increasing net primary productivity in higher features and CH4emissions in some lower and higher features since 2008, attributed mostly to recent rises in precipitation. Small‐scale variation in surface elevation causes large spatial variation of greenhouse gas (GHG) exchanges and therefore should be considered in estimates of GHG exchange in polygonal landscapes. Topographic effects on CO2fluxes caused lower features to be net C sinks and higher features to be near C neutralTopographic effects on CH4fluxes caused lower features to be larger CH4sources and higher features to be smaller CH4sourcesMuch of spatial and temporal variations in CO2and CH4fluxes were attributed in the model to topographic effects of water and snow movement