Multi-year observations reveal a larger than expected autumn respiration signal across northeast Eurasia
oleh: B. Byrne, J. Liu, J. Liu, Y. Yi, Y. Yi, A. Chatterjee, S. Basu, S. Basu, R. Cheng, R. Doughty, R. Doughty, F. Chevallier, K. W. Bowman, K. W. Bowman, N. C. Parazoo, D. Crisp, X. Li, J. Xiao, S. Sitch, B. Guenet, F. Deng, M. S. Johnson, S. Philip, P. C. McGuire, C. E. Miller
| Format: | Article |
|---|---|
| Diterbitkan: | Copernicus Publications 2022-10-01 |
Deskripsi
<p>Site-level observations have shown pervasive cold season CO<span class="inline-formula"><sub>2</sub></span> release across Arctic and boreal ecosystems, impacting annual carbon budgets. Still, the seasonality of CO<span class="inline-formula"><sub>2</sub></span> emissions are poorly quantified across much of the high latitudes due to the sparse coverage of site-level observations. Space-based observations provide the opportunity to fill some observational gaps for studying these high-latitude ecosystems, particularly across poorly sampled regions of Eurasia. Here, we show that data-driven net ecosystem exchange (NEE) from atmospheric CO<span class="inline-formula"><sub>2</sub></span> observations implies strong summer uptake followed by strong autumn release of CO<span class="inline-formula"><sub>2</sub></span> over the entire cold northeastern region of Eurasia during the 2015–2019 study period. Combining data-driven NEE with satellite-based estimates of gross primary production (GPP), we show that this seasonality implies less summer heterotrophic respiration (<span class="inline-formula"><i>R</i><sub>h</sub></span>) and greater autumn <span class="inline-formula"><i>R</i><sub>h</sub></span> than would be expected given an exponential relationship between respiration and surface temperature. Furthermore, we show that this seasonality of NEE and <span class="inline-formula"><i>R</i><sub>h</sub></span> over northeastern Eurasia is not captured by the TRENDY v8 ensemble of dynamic global vegetation models (DGVMs), which estimate that 47 %–57 % (interquartile range) of annual <span class="inline-formula"><i>R</i><sub>h</sub></span> occurs during August–April, while the data-driven estimates suggest 59 %–76 % of annual <span class="inline-formula"><i>R</i><sub>h</sub></span> occurs over this period. We explain this seasonal shift in <span class="inline-formula"><i>R</i><sub>h</sub></span> by respiration from soils at depth during the zero-curtain period, when sub-surface soils remain unfrozen up to several months after the surface has frozen. Additional impacts of physical processes related to freeze–thaw dynamics may contribute to the seasonality of <span class="inline-formula"><i>R</i><sub>h</sub></span>. This study confirms a significant and spatially extensive early cold season CO<span class="inline-formula"><sub>2</sub></span> efflux in the permafrost-rich region of northeast Eurasia and suggests that autumn <span class="inline-formula"><i>R</i><sub>h</sub></span> from subsurface soils in the northern high latitudes is not well captured by current DGVMs.</p>