Climatic warming is predicted to affect high-latitude habitats, such as boreal peatlands, at a larger magnitude than the global average. The controls on the breakdown of organic matter in peatlands are complex; it’s unclear how climatic warming will affect the stability of the large carbon pool that’s currently stored in peatlands. To investigate this, we collected soil cores from three boreal habitats along a hydrological transect (Bog, Intermediate, and Upland Forest) in Finland, and incubated ex-situ for 140 days. Each soil horizon was incubated in three temperatures (0°C, 4°C, 20°C). Here, we found the Intermediate site had the largest CO2 production considering the entirety of the soil column (per gram dry weight). Statistical analysis found that sample C content was the most indicative independent variable to predict sample CO2 production. Each soil horizon displayed a different magnitude of response to the temperature incubations (Q10s ranged from 0.60-2.33), and through microbial relative abundance analysis we found that the microbial community structure had significant differences between both habitat and depth of sample origin. Coupling these methods, and the fine scale of the both vertical (soil column horizons) and horizontal (along a hydrological gradient through distinct habitats) transects gives us a novel perspective on the controls of microbial respiration rates. Our results stress that large scale modeling efforts of carbon dynamics should prioritize both soil carbon quantity and quality.

The long-term net sink of carbon (C), nitrogen (N) and greenhouse gases (GHGs) in the northern permafrost region is projected to weaken or shift under climate change. But large uncertainties remain, even on present-day GHG budgets. We compare bottom-up (data-driven upscaling, process-based models) and top-down budgets (atmospheric inversion models) of the main GHGs (CO2, CH4, and N2O) and lateral fluxes of C and N across the region over 2000-2020. Bottom-up approaches estimate higher land to atmosphere fluxes for all GHGs compared to top-down atmospheric inversions. Both bottom-up and top-down approaches respectively show a net sink of CO2 in natural ecosystems (-31 (-667, 559) and -587 (-862, -312), respectively) but sources of CH4 (38 (23, 53) and 15 (11, 18) Tg CH4-C yr-1) and N2O (0.6 (0.03, 1.2) and 0.09 (-0.19, 0.37) Tg N2O-N yr-1) in natural ecosystems. Assuming equal weight to bottom-up and top-down budgets and including anthropogenic emissions, the combined GHG budget is a source of 147 (-492, 759) Tg CO2-Ceq yr-1 (GWP100). A net CO2 sink in boreal forests and wetlands is offset by CO2 emissions from inland waters and CH4 emissions from wetlands and inland waters, with a smaller additional warming from N2O emissions. Priorities for future research include representation of inland waters in process-based models and compilation of process-model ensembles for CH4 and N2O. Discrepancies between bottom-up and top-down methods call for analyses of how prior flux ensembles impact inversion budgets, more in-situ flux observations and improved resolution in upscaling.

The northern permafrost region has been projected to shift from a net sink to a net source of carbon under global warming. However, estimates of the contemporary net greenhouse gas (GHG) balance and budgets of the permafrost region remain highly uncertain. Here we construct the first comprehensive bottom-up budgets of CO2, CH4, and N2O across the terrestrial permafrost region using databases of more than 1000 in-situ flux measurements and a land cover-based ecosystem flux upscaling approach for the period 2000-2020. Estimates indicate that the permafrost region emitted a mean annual flux of 0.36 (-620, 652) Tg CO2-C y-1, 38 (21, 53) Tg CH4-C y-1, and 0.62 (0.03, 1.2) Tg N2O-N y-1 to the atmosphere throughout the period. While the region was a net source of CH4 and N2O, the CO2 budget was near neutral with large uncertainties. Terrestrial ecosystems remained a CO2 sink, but emissions from fire disturbances and inland waters largely offset the sink in vegetated ecosystems. Including lateral fluxes, the permafrost region was a net source of C and N, releasing 136 (-517, 821) Tg C y-1 and 3.2 (1.9, 4.8) Tg N y-1. Large uncertainty ranges in these estimates point to a need for further expansion of monitoring networks, continued data synthesis efforts, and better integration of field observations, remote sensing data, and ecosystem models to constrain the contemporary net GHG budgets of the permafrost region and track their future trajectory.

The Arctic is warming four times faster than the global average, resulting in widespread ground thaw and state changes. Due to the rapid rate and large scale of ecosystem shifts, identifying and understanding Arctic boreal zone changes and feedbacks requires frequent observations across multiple scales. The last decade has witnessed significant increases in the number and coverage of in-situ, airborne, and satellite observations. However, additional resolution, coverage, and sustained, long-term time series data records are urgently required to characterize and understand the considerable heterogeneity of Northern permafrost environments. Here, we review the physical and technical gaps that limit the ability to detect rapid state changes and tipping points in permafrost ecosystems. Understanding and accurately forecasting changes to the Arctic is an essential component of managing climate change in this rapidly transforming system.