Interannual variations in Siberian carbon uptake and carbon release period

Abstract

Winters with higher-than-average temperatures are expected to enhance the respiratory release of CO2, thereby weakening the annual net terrestrial carbon sink. Using the 2010–2021 atmospheric CO2 record from the Zotino Tall Tower Observatory (ZOTTO) located at 60°48′ N, 89°21′ E, this study analyses interannual changes in the timing and intensity of the carbon uptake and release periods (CUP and CRP, respectively) over central Siberia. We complement our CO2 mole fraction analysis with the atmospheric inversion results to disentangle the effects of meteorological variability from the ecosystem's response to climate variability at a regional scale. From the observational data, CRP length and amplitude significantly increased between 2010 and 2021. Similarly, CUP length and amplitude have shown a positive but weaker trend since 2010, suggesting that increased CO2 release during cold months offsets the uptake during the growing season. This suggests that during 2010–2021, climate warming did not lead to higher annual net CO2 uptake despite the enhanced growing season uptake because cold-season respiration has also increased due to warming. The observational analysis further showed the influence of two extreme events: the 2012 wildfire and the 2020 heat wave. However, analysis of the inversion-derived net ecosystem exchange flux for the ZOTTO region did not reveal these trends or extreme events. Therefore, while ZOTTO data contain substantial information on the magnitude of the Siberian carbon balance (without further data from additional stations), we could not attribute a distinct contribution of ecosystems in the ZOTTO region of influence to the observed trends and extremes.