Changes in terrestrial CO2 budget in Siberia in the past three decades

Abstract:

Siberia is one of the regions where significant warming is proceeding, and the warming might cause changes in terrestrial carbon cycle. We analyzed interannual and decadal changes in terrestrial CO₂ fluxes in the regions using multiple data sets, such as empirically estimated carbon fluxes based on multiple eddy-covariance sites (empirical upscaling; Support Vector Regression with AsiaFlux data), satellite-based vegetation index data, multiple terrestrial carbon cycle models from Asia-MIP (e.g. BEAMS, Biome-BGC, SEIB-DGVM, and VISIT), and atmospheric inverse models (e.g. ACTM, JMA, NICAM-TM) for the past 3 decades (1980s, 1990s, and 2000s).

First, we checked the consistency in interannual variation of net carbon exchange between empirical upscaling and Asia-MIP model for 2001-2011 period, and found these two estimations show overall consistent interannual variation. Second, we analyzed net carbon exchange form Asia-MIP models and atmospheric inversions for the past three decades, and found persistent increases in terrestrial CO₂ sink from two estimates. Magnitudes of estimated terrestrial CO₂ sinks are also consistent (e.g. Asia-MIP: 0.2 PgC yr^-1 in 1980s and 0.3 PgC yr^-1 in 2000s and Inversions: 0.2 PgC yr^-1 in 1980s and 0.5 PgC/yr in 2000s). We further analyzed the cause of persistent increases in CO₂ uptake in the region using Asia-MIP model outputs, and climate changes (both warming and increases in water availability) and CO₂ fertilization plays almost equivalent roles in sink increases. In addition, both gross primary productivity (GPP) and ecosystem respiration (RE) were increased, but increase in GPP was larger than that in RE.