Carbon uptake in Eurasian boreal forests dominates the high‐latitude net ecosystem carbon budget

Abstract

Arctic‐boreal landscapes are experiencing profound warming, along with changes in ecosystem moisture status and disturbance from fire. This region is of global importance in terms of carbon feedbacks to climate, yet the sign (sink or source) and magnitude of the Arctic‐boreal carbon budget within recent years remains highly uncertain. Here, we provide new estimates of recent (2003–2015) vegetation gross primary productivity (GPP), ecosystem respiration (Reco), net ecosystem CO2 exchange (NEE; Reco − GPP), and terrestrial methane (CH4) emissions for the Arctic‐boreal zone using a satellite data‐driven process‐model for northern ecosystems (TCFM‐Arctic), calibrated and evaluated using measurements from >60 tower eddy covariance (EC) sites. We used TCFM‐Arctic to obtain daily 1‐km2 flux estimates and annual carbon budgets for the pan‐Arctic‐boreal region. Across the domain, the model indicated an overall average NEE sink of −850 Tg CO2‐C year−1. Eurasian boreal zones, especially those in Siberia, contributed to a majority of the net sink. In contrast, the tundra biome was relatively carbon neutral (ranging from small sink to source). Regional CH4 emissions from tundra and boreal wetlands (not accounting for aquatic CH4) were estimated at 35 Tg CH4‐C year−1. Accounting for additional emissions from open water aquatic bodies and from fire, using available estimates from the literature, reduced the total regional NEE sink by 21% and shifted many far northern tundra landscapes, and some boreal forests, to a net carbon source. This assessment, based on in situ observations and models, improves our understanding of the high‐latitude carbon status and also indicates a continued need for integrated site‐to‐regional assessments to monitor the vulnerability of these ecosystems to climate change.

Persistent net release of carbon dioxide and methane from an Alaskan lowland boreal peatland complex

“…(2020) applied a process‐based model to simulate North American peatland C storage over the last 12,000 years and found that these peatlands accumulated 85–174 Pg C over the study period, but that peat decomposition and permafrost degradation complicate future predictions of the sink strength (Jones et al., 2023). Two studies conducted at the pan‐Arctic scale indicate, based on CO 2 alone, the boreal region remains a net sink of CO 2 for the years 1990–2015 with much of this sink strength derived from the boreal uplands, particularly those in the Eurasian boreal region, and Siberia in particular (Virkkala et al., 2021; Watts et al., 2023). Considering only evergreen boreal forests, recent work finds a net sink of 0.4 Pg C year −1 between 1981–2018, but there is no trend toward increasing in CO 2 uptake as increases in GPP are compensated for by losses due to ER, with large interannual variability (Pulliainen et al., 2022).…”

“…Zhuang et al (2020) applied a process-based model to simulate North American peatland C storage over the last 12,000 years and found that these peatlands accumulated 85-174 Pg C over the study period, but that peat decomposition and permafrost degradation complicate future predictions of the sink strength (Jones et al, 2023). Two and Siberia in particular (Virkkala et al, 2021;Watts et al, 2023).…”

Ecosystem CO2 Exchange and Its Economic Implications in Northern Permafrost Regions in the 21st Century

“…Furthermore, permafrost regions have a great potential to emit much more CH 4 (Treat et al., 2018; Zona et al., 2016). It was estimated that regional CH 4 emissions from tundra and boreal wetlands were approximately 35 Tg CH 4 ‐C year −1 using a satellite data‐driven process‐model for northern ecosystems (Watts et al., 2023). Similar to CO 2 emissions, understanding CH 4 emission magnitude and its driving factors in the growing and nongrowing seasons still requires more in situ observations to narrow the uncertainties of the carbon budget.…”

Permafrost Carbon: Progress on Understanding Stocks and Fluxes Across Northern Terrestrial Ecosystems

“…Wetlands and lakes have differing CH 4 emissions and processes (Kuhn et al., 2021b; Wik et al., 2016), but distinguishing these landforms in observations and remote sensing images can be difficult, leading to possible double counting of emissions sources (Thornton et al., 2016). Hybrid process modeling together with remote sensing and eddy covariance data have been used to estimate wetland CH 4 fluxes relatively accurately (Watts et al., 2023), which incorporates important factors such as soil moisture, temperature, vegetation characteristics, and hydrological dynamics to estimate wetland CH 4 fluxes.…”