Accelerated warming of the Arctic can affect the global climate system by thawing permafrost and exposing organic carbon in soils to decompose and release greenhouse gases into the atmosphere. We used a process-based biosphere model (DVM-DOS-TEM) designed to simulate biophysical and biogeochemical interactions between the soil, vegetation, and atmosphere. We varied soil and environmental parameters to assess the impact on cryohydrological and biogeochemical outputs in the model. We analyzed the responses of ecosystem carbon balances to permafrost thaw by running site-level simulations at two long-term tundra ecological monitoring sites in Alaska: Eight Mile Lake (EML) and Imnavait Creek Watershed (IMN), which are characterized by similar tussock tundra vegetation but differing soil drainage conditions and climate. Model outputs showed agreement with field observations at both sites for soil physical properties and ecosystem CO2fluxes. Model simulations of Net Ecosystem Exchange (NEE) showed an overestimation during the frozen season (higher CO2emissions) at EML with a mean NEE of 26.98 ± 4.83 gC/m2/month compared to observational mean of 22.01 ± 5.67 gC/m2/month, and during the fall months at IMN, with a modeled mean of 19.21 ± 7.49 gC/m2/month compared to observation mean of 11.9 ± 4.45 gC/m2/month. Our results underscore the importance of representing the impact of soil drainage conditions on the thawing of permafrost soils, particularly poorly drained soils, which will drive the magnitude of carbon released at sites across the high-latitude tundra. These findings can help improve predictions of net carbon releases from thawing permafrost, ultimately contributing to a better understanding of the impact of Arctic warming on the global climate system.
This content will become publicly available on January 18, 2025
Trawling the seafloor can disturb carbon that took millennia to accumulate, but the fate of that carbon and its impact on climate and ecosystems remains unknown. Using satellite-inferred fishing events and carbon cycle models, we find that 55-60% of trawling-induced aqueous CO2is released to the atmosphere over 7-9 years. Using recent estimates of bottom trawling’s impact on sedimentary carbon, we found that between 1996-2020 trawling could have released, at the global scale, up to 0.34-0.37 Pg CO2yr-1to the atmosphere, and locally altered water pH in some semi-enclosed and heavy trawled seas. Our results suggest that the management of bottom-trawling efforts could be an important climate solution.
more » « less- Award ID(s):
- 1948955
- PAR ID:
- 10519191
- Publisher / Repository:
- Frontiers
- Date Published:
- Journal Name:
- Frontiers in Marine Science
- Volume:
- 10
- ISSN:
- 2296-7745
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Large stocks of soil carbon (C) and nitrogen (N) in northern permafrost soils are vulnerable to remobilization under climate change. However, there are large uncertainties in present‐day greenhouse gas (GHG) budgets. We compare bottom‐up (data‐driven upscaling and process‐based models) and top‐down (atmospheric inversion models) budgets of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) as well as lateral fluxes of C and N across the region over 2000–2020. Bottom‐up approaches estimate higher land‐to‐atmosphere fluxes for all GHGs. Both bottom‐up and top‐down approaches show a sink of CO2in natural ecosystems (bottom‐up: −29 (−709, 455), top‐down: −587 (−862, −312) Tg CO2‐C yr−1) and sources of CH4(bottom‐up: 38 (22, 53), top‐down: 15 (11, 18) Tg CH4‐C yr−1) and N2O (bottom‐up: 0.7 (0.1, 1.3), top‐down: 0.09 (−0.19, 0.37) Tg N2O‐N yr−1). The combined global warming potential of all three gases (GWP‐100) cannot be distinguished from neutral. Over shorter timescales (GWP‐20), the region is a net GHG source because CH4dominates the total forcing. The net CO2sink in Boreal forests and wetlands is largely offset by fires and inland water CO2emissions as well as CH4emissions from wetlands and inland waters, with a smaller contribution from N2O emissions. Priorities for future research include the representation of inland waters in process‐based models and the compilation of process‐model ensembles for CH4and N2O. Discrepancies between bottom‐up and top‐down methods call for analyses of how prior flux ensembles impact inversion budgets, more and well‐distributed in situ GHG measurements and improved resolution in upscaling techniques.
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Abstract Non‐growing season CO2emissions from Arctic tundra remain a major uncertainty in forecasting climate change consequences of permafrost thaw. We present the first time series of soil and microbial CO2emissions from a graminoid tundra based on year‐round in situ measurements of the radiocarbon content of soil CO2(Δ14CO2) and of bulk soil C (Δ14C), microbial activity, and temperature. Combining these data with land‐atmosphere CO2exchange allows estimates of the proportion and mean age of microbial CO2emissions year‐round. We observe a seasonal shift in emission sources from fresh carbon during the growing season (August Δ14CO2 = 74 ± 4.7‰, 37% ± 3.4% microbial, mean ± se) to increasingly older soil carbon in fall and winter (March Δ14CO2 = 22 ± 1.3‰, 47% ± 8% microbial). Thus, rising soil temperatures and emissions during fall and winter are depleting aged soil carbon pools in the active layer and thawing permafrost and further accelerating climate change.
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