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- Virkkala, Anna Maria, et al.
(författare)
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Statistical upscaling of ecosystem CO2 fluxes across the terrestrial tundra and boreal domain : Regional patterns and uncertainties
- 2021
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 27:17, s. 4040-4059
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Tidskriftsartikel (refereegranskat)abstract
- The regional variability in tundra and boreal carbon dioxide (CO2) fluxes can be high, complicating efforts to quantify sink-source patterns across the entire region. Statistical models are increasingly used to predict (i.e., upscale) CO2 fluxes across large spatial domains, but the reliability of different modeling techniques, each with different specifications and assumptions, has not been assessed in detail. Here, we compile eddy covariance and chamber measurements of annual and growing season CO2 fluxes of gross primary productivity (GPP), ecosystem respiration (ER), and net ecosystem exchange (NEE) during 1990–2015 from 148 terrestrial high-latitude (i.e., tundra and boreal) sites to analyze the spatial patterns and drivers of CO2 fluxes and test the accuracy and uncertainty of different statistical models. CO2 fluxes were upscaled at relatively high spatial resolution (1 km2) across the high-latitude region using five commonly used statistical models and their ensemble, that is, the median of all five models, using climatic, vegetation, and soil predictors. We found the performance of machine learning and ensemble predictions to outperform traditional regression methods. We also found the predictive performance of NEE-focused models to be low, relative to models predicting GPP and ER. Our data compilation and ensemble predictions showed that CO2 sink strength was larger in the boreal biome (observed and predicted average annual NEE −46 and −29 g C m−2 yr−1, respectively) compared to tundra (average annual NEE +10 and −2 g C m−2 yr−1). This pattern was associated with large spatial variability, reflecting local heterogeneity in soil organic carbon stocks, climate, and vegetation productivity. The terrestrial ecosystem CO2 budget, estimated using the annual NEE ensemble prediction, suggests the high-latitude region was on average an annual CO2 sink during 1990–2015, although uncertainty remains high.
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| 2. |
- Väliranta, Minna, et al.
(författare)
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Warming climate forcing impact from a sub-arctic peatland as a result of late Holocene permafrost aggradation and initiation of bare peat surfaces
- 2021
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 264
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Tidskriftsartikel (refereegranskat)abstract
- Effects of permafrost aggradation on greenhouse gas (GHG) dynamics and climate forcing have not been previously quantified. Here, we reconstruct changes in GHG balances over the late Holocene for a sub-arctic peatland by applying palaeoecological data combined with measured GHG flux data, focusing on the impact of permafrost aggradation in particular. Our data suggest that permafrost initiation around 3000 years ago resulted in GHG emissions, thereby slightly weakening the general long-term peatland cooling impact. As a novel discovery, based on our chronological data of bare peat surfaces, we found that current sporadic bare peat surfaces in subarctic regions are probably remnants of more extensive bare peat areas formed by permafrost initiation. Paradoxically, our data suggest that permafrost initiation triggered by the late Holocene cooling climate generated a positive radiative forcing and a short-term climate warming feedback, mitigating the general insolation-driven late Holocene summer cooling trend. Our work with historical data demonstrates the importance of permafrost peatland dynamics for atmospheric GHG concentrations, both in the past and future. It suggests that, while thawing permafrost is likely to initially trigger a change towards wetter conditions and consequent increase in CH4 forcing, eventually the accelerated C uptake capacity under warmer climate may overcome the thaw effect when a new hydrological balance becomes established.
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