| Summary: | These data sets are the results of a model-data analysis of the contemporary C balance of the Arctic system in which the land and ocean area of the Arctic Basin is treated as a linked system of CO2 and CH4 exchange across terrestrial, marine and atmospheric components. The study area for the terrestrial component of the Arctic Basin is defined as the land area within the watersheds of the major rivers that drain into the Arctic Ocean (Lammers et al., 2001). Several process-based tools were used to conduct this analysis of C dynamics across the Arctic Basin between years 1997 and 2006 through simulations of land atmosphere CO2 and CH4 exchange, the transfer of land-based C to the Arctic Ocean, and ocean-atmosphere CO2 exchange. CO2 and CH4 exchange between the terrestrial ecosystems of the basin and the atmosphere, along with the export of dissolved organic C (DOC) to the Arctic Ocean, were estimated using the Terrestrial Ecosystem Model (TEM). The TEM considers the effects of a number of factors on its simulations of C dynamics including changes in atmospheric CO2, tropospheric ozone, nitrogen deposition, climate, and disturbance/land use including fire, forest harvest, and agricultural establishment/abandonment. TEM also calculates pyrogenic emissions of CO2, CH4, and CO from the combustion of vegetation and soil carbon in wildfires. The DOC leaching dynamics of TEM are a function of soil C decomposition rate, soil DOC concentration and water flux through the soil. We used the methane dynamics module of TEM (MDM-TEM) to estimate the exchange of CH4 with atmosphere of both wetlands, which generally emit CH4 to the atmosphere, and uplands, which generally consume CH4 from the atmosphere. The MDM-TEM considers the effects of a number of factors on its simulations of CH4 dynamics including the area of wetlands, fluctuations in the water table of wetlands, temperature, and labile carbon inputs into the soil solution derived from the net primary production (NPP) estimates of TEM. The MIT ocean biogeochemistry model simulated the net exchange of CO2 with the atmosphere as driven by changes in sea ice, water temperature, ocean circulation, and DOC inputs from TEM. The results of these simulations were compared with estimates of CO2 and CH4 exchange from atmospheric inversion models and with observations of terrestrial C export from Arctic watersheds. The simulated transfer of land-based C to the Arctic Ocean was compared against estimates based on a sampling of DOC export from major Arctic rivers (McClelland et al., 2008). The land-atmosphere CO2 exchange estimate was compared with results from the TransCom3 atmospheric inversion model inter-comparison project (Gurney et al., 2008), and CH4 to results from atmospheric inversion-estimated surface emissions (Chen and Prinn, 2006). To compare the “bottom-up” results from our model simulations with the “top down” estimates from these inversion studies, we summarize our estimates of surface-atmosphere CO2 and CH4 exchange for the land and ocean area matching the three high-latitude regions defined in the Transcom 3 model experiments (Gurney et al., 2002), namely the Boreal North America, Boreal Asia and Northern Ocean regions.
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