Advancing permafrost carbon climate feedback-improvements and evaluations of the Norwegian Earth System Model with observations

Permafrost soil, soil that is frozen for more than two consecutive years, stores large amounts of carbon as soil organic matter. This amount of carbon is approximately twice more than what is in the atmosphere and far more than what is stored in global vegetation. Permafrost carbon was previously thought to be very stable as we believed permafrost was 'permanently frozen'. Global scale warming has led to permafrost to thaw. Some may say permafrost is 'a ticking time bomb' under current rate of global scale warming, because when permafrost thaws the carbon stored in permafrost can be released back to the atmosphere as greenhouse gases, carbon dioxide (CO2) and methane (CH4), from microbial decomposition of soil organic matter. Because warming induces permafrost to thaw faster and permafrost thawing accelerates release of greenhouse gases, which could cause additional warming, this phenomenon is called permafrost carbon-climate feedback cycle. There are many aspects to consider, when accurately estimating how much greenhouse gas emissions there is with permafrost thawing. First, warming not only enhances greenhouse gas release, but also enhances greenhouse gas uptake. This is because vegetation in the Arctic will grow faster and larger with warming. Second, permafrost thaw affects the land surface processes such that permafrost affected ground can collapse with thawing of ground ice and this area can be filled with water, sometimes forming mires. When the soil is submerged under water, the soil environment becomes anaerobic, which means there is lack of oxygen (O2). Under anaerobic conditions, microbial decomposition can produce CH4, which is a much more toxic greenhouse gas than CO2. But anaerobic process is slower than aerobic process that only releases CO2. Third, only certain tools can predict how much of the greenhouse gas emissions from permafrost thawing will affect global scale warming. These tools are called Earth System Models, in other words, large scale climate models. Last, the harsh environmental conditions make it difficult for researchers to collect enough data for the data and models to be validated and evaluated. All of these things need to be taken into consideration for us to more accurately understand how permafrost thaw and changes in Arctic environment affect greenhouse gas balance. In our research, we monitored the environmental conditions as well as CO2 and CH4 emissions along a permafrost thaw gradient. In the gradient, the more permafrost thaws, the more anaerobic soil environment it gets. As a result, we can better associate the degree of permafrost thawing and soil inundation with CO2 and CH4 emissions and uptake from permafrost soils. Our results show that ecosystem takes up more carbon because of vegetation growth as permafrost thaws. This is just during the summer season. But overall, permafrost thawing accelerates CO2 release as well as CH4 release.

Our observations, and statistical modeling results, suggest that permafrost thaw and landscape subsidence, intermediate slumping and pond formation, increases net annual carbon loss in this widespread subarctic wetland type. Generally, thaw slumping and pond formation does not change CO2 emissions substantially as inundated plots had similar CO2 balance as on palsas. However, CH4 release greatly increased across the permafrost thaw gradient. During the growing season, vegetated palsas were small sinks of atmospheric CH4, whereas permafrost thaw slumping and pond formation increased CH4 efflux dramatically relative to palsas. Soil profile CO2 and CH4 concentrations were overall highly enriched relative to palsa profiles, reflecting soil conditions with inundated pore space and low oxygen availability along the permafrost thaw gradient. Our results suggest that permafrost thaw, both intermediate slumping and pond formation, currently increases overall growing season carbon release.

FEEDBACK project is proposed research project under the FRINATEK young research talent call for proposals. FEEDBACK aims to build accurate predictions of future climate feedback cycles from thawing permafrost, including the role of permafrost carbon (C). We will improve permafrost biogeochemistry module based on process-level understanding gained from systematic field observations. In addition, this project will develop a new observational scheme that will provide seamless process level understanding of permafrost biogeochemistry under varying soil hydrological regimes and will collect much-needed observational data for evaluating the model simulations. This project will be in the forefront of advancing our understandings on climate system and future climate projections. As a result, FEEDBACK will strengthen the terrestrial biogeochemistry research at the leading climate research institute, the Bjerknes Centre for Climate Research and bridge close collaborations across 5 world class national and international institutions to strengthen the knowledge in the interaction between the terrestrial and the climate system. Along with its scientific contributions, this project will enhance project leading and supervisory skills for the leader (Hanna Lee), by which will result in a multifaceted early career researcher (postdoc), who will become an expert in observations, data synthesis, and modeling in the framework of permafrost, global C cycling, and climate change. FEEDBACK is a highly innovative project that operates across traditional boundaries among the research arenas such as field-based observations, statistical data synthesis and model parameterization, and ESM development and evaluation. The project leader, partners, and collaborators of FEEDBACK have strong track records in these fields, offering unique and excellent potential to significantly transport the current knowledge no other group can offer.