[A-CG39] Biogeochemical cycles in Land Ecosystem

[ACG39-11] Autumn cooling paused increased CO₂ release in central Eurasia

*Masayuki Kondo¹, Motoki Sasakawa², Toshinobu Machida², Tetsuya Hiyama³ (1.The IDEC institute, Hiroshima University, 2.National Institute for Environmental Studies, 3.Institute for Space–Earth Environmental Research, Nagoya University)

Keywords:Autumn cooling, CO2 flux, Central Siberia

Recent autumn warming in northern latitudes has facilitated an increase in terrestrial ecosystem respiration (TER) more than that in gross primary productivity (GPP), leading to a net loss of CO2 from the land to the atmosphere in autumn. Conversely, autumn cooling is expected to induce a greater decrease in TER than in GPP, thus leading to a net increase in autumn CO2 uptake. However, a recent study reported an increase in net CO2 release in northern autumn cooling from 2004 to 20183, indicating that both the autumn warming and cooling result in net CO2 release. Here, we show that the conclusion regarding net CO2 release under autumn cooling was flawed owing to the inappropriate choice of the autumn period, which resulted in overlooking regions such as central Eurasia, where the 2004–2018 autumn cooling most affected CO2 fluxes. Empirical upscaling of eddy flux observations (FLUXCOM) and atmospheric CO2 measurements from seven towers suggested that the increased net CO2 release paused during the 2004–2018 autumn cooling in central Eurasia. The results reported by the recent study are likely biased toward CO2 release as their assessment involves regions including North America where the 2004–2018 autumn cooling had little effect (rather, the autumn warming effect was more profound) on CO2 fluxes.

The authors acknowledge support from JSPS KAKENHI (Grant Numbers 19H05668).