Multi-year observations reveal a larger than expected autumn respiration signal across northeast Eurasia

[摘要] Site-level observations have shown pervasive cold season CO 2 release across Arctic and boreal ecosystems, impacting annual carbon budgets. Still, the seasonality of CO 2 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 2 observations implies strong summer uptake followed by strong autumn release of CO 2 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 ( R h ) and greater autumn R h than would be expected given an exponential relationship between respiration and surface temperature. Furthermore, we show that this seasonality of NEE and R h 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 R h occurs during August–April, while the data-driven estimates suggest 59 %–76 % of annual R h occurs over this period. We explain this seasonal shift in R h 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 R h . This study confirms a significant and spatially extensive early cold season CO 2 efflux in the permafrost-rich region of northeast Eurasia and suggests that autumn R h from subsurface soils in the northern high latitudes is not well captured by current DGVMs.

[学科分类] 大气科学