Biogeophysical feedbacks enhance the Arctic terrestrial carbon sink in regional Earth system dynamics

[摘要] Continued warming of the Arctic will likely accelerate terrestrial carbon(C) cycling by increasing both uptake and release of C. Yet, there are stilllarge uncertainties in modelling Arctic terrestrial ecosystems as a sourceor sink of C. Most modelling studies assessing or projecting the future fateof C exchange with the atmosphere are based on either stand-aloneprocess-based models or coupled climate–C cycle general circulation models,and often disregard biogeophysical feedbacks of land-surface changes to theatmosphere. To understand how biogeophysical feedbacks might impact on bothclimate and the C budget in Arctic terrestrial ecosystems, we apply theregional Earth system model RCA-GUESS over the CORDEX-Arctic domain. Themodel is forced with lateral boundary conditions from an EC-Earth CMIP5climate projection under the representative concentration pathway (RCP) 8.5 scenario. We perform two simulations,with or without interactive vegetation dynamics respectively, to assess theimpacts of biogeophysical feedbacks. Both simulations indicate that Arcticterrestrial ecosystems will continue to sequester C with an increased uptakerate until the 2060–2070s, after which the C budget will return to a weak Csink as increased soil respiration and biomass burning outpaces increasednet primary productivity. The additional C sinks arising from biogeophysicalfeedbacks are approximately 8.5 Gt C, accounting for 22% of the total Csinks, of which 83.5% are located in areas of extant Arctic tundra. Twoopposing feedback mechanisms, mediated by albedo and evapotranspirationchanges respectively, contribute to this response. The albedo feedbackdominates in the winter and spring seasons, amplifying the near-surfacewarming by up to 1.35 °C in spring, while the evapotranspirationfeedback dominates in the summer months, and leads to a cooling of up to0.81 °C. Such feedbacks stimulate vegetation growth due to anearlier onset of the growing season, leading to compositional changes inwoody plants and vegetation redistribution.

[学科分类] 地球化学与岩石