Assessment of model estimates of land-atmosphere CO2 exchange across Northern Eurasia

[摘要] A warming climate is altering land-atmosphere exchanges of carbon, with apotential for increased vegetation productivity as well as the mobilizationof permafrost soil carbon stores. Here we investigate land-atmosphere carbondioxide (CO₂) cycling through analysis of net ecosystem productivity (NEP)and its component fluxes of gross primary productivity (GPP) and ecosystemrespiration (ER) and soil carbon residence time, simulated by a set of landsurface models (LSMs) over a region spanning the drainage basin of NorthernEurasia. The retrospective simulations cover the period 1960–2009 at 0.5° resolution, which is a scale common among many global carbon andclimate model simulations. Model performance benchmarks were drawn fromcomparisons against both observed CO₂ fluxes derived from site-based eddycovariance measurements as well as regional-scale GPP estimates based onsatellite remote-sensing data. The site-based comparisons depict a tendencyfor overestimates in GPP and ER for several of the models, particularly atthe two sites to the south. For several models the spatial pattern in GPPexplains less than half the variance in the MODIS MOD17 GPP product. Acrossthe models NEP increases by as little as 0.01 to as much as 0.79 g C m⁻² yr⁻²,equivalent to 3to 340 % of the respective model means, over theanalysis period. For the multimodel average the increase is 135 % of the meanfrom the first to last 10 years of record (1960–1969 vs. 2000–2009), with aweakening CO₂ sink over the latter decades. Vegetation net primaryproductivity increased by 8 to 30 % from the first to last 10 years,contributing to soil carbon storage gains. The range in regional mean NEPamong the group is twice the multimodel mean, indicative of the uncertaintyin CO₂ sink strength. The models simulate that inputs to the soil carbonpool exceeded losses, resulting in a net soil carbon gain amid a decrease inresidence time. Our analysis points to improvements in model elementscontrolling vegetation productivity and soil respiration as being needed forreducing uncertainty in land-atmosphere CO₂ exchange. These advances willrequire collection of new field data on vegetation and soil dynamics, thedevelopment of benchmarking data sets from measurements and remote-sensingobservations, and investments in future model development and intercomparisonstudies.

[学科分类] 地球化学与岩石