Arctic Biogeochemical Response to Permafrost Thaw (ABRUPT)

Active

By Ecosystems Land Change Science Program January 25, 2021

Warming and thawing of permafrost soils in the Arctic is expected to become widespread over the coming decades. Permafrost thaw changes ecosystem structure and function, affects resource availability for wildlife and society, and decreases ground stability which affects human infrastructure. Since permafrost soils contain about half of the global soil carbon (C) pool, the magnitude of C losses from permafrost thaw are critically important to understanding the global carbon cycle, known as the permafrost carbon feedback. Recently wintertime processes have been shown to be a critical yet understudied component of the permafrost carbon feedback. Therefore our goal is to understand wintertime processes controlling greenhouse gas fluxes (CO2 and CH4) from thawing permafrost soils in Alaska. Specifically, we are interested in measuring and modelling the presence of small amounts of liquid water within frozen soils that can fuel large changes in soil microbial activity and winter greenhouse gas fluxes.

Statement of Problem: Up to half of the annual arctic methane (CH₄) and carbon dioxide (CO₂) flux from soils to the atmosphere occurs during the winter, but the exact source of greenhouse gas (GHG) and how its production or consumption might vary among stages of permafrost thaw or in different locations is poorly understood. Greenhouse gases in winter can come from the surface active layer (the zone of surface soil that thaws and refreezes each year), the underlying talik (a deeper zone of soil that never freezes and is potentially a year-round source of microbial activity), and/or the deeper permafrost which, if near 0 °C, can contain significant amounts of unfrozen water (Figure 1).

diagram of ecosystem transition from permafrost plateau to fen — Figure 1. Characterization of the ecosystem transitions studied in this experiment and their influence on talik development and greenhouse gas production. Four sites herein are 1) permafrost plateaus with stable permafrost and therefore no talik development, 2) permafrost plateaus with observed talik development, 3) bog system with talik underlain by permafrost, and 4) fen ecosystem with deep talik and no permafrost. As taliks increase in size we expect increasing winter greenhouse gas emissions.

ice-rich permafrost — Ice-rich permafrost cross section.

Why this Research is Important: Our research improves the fundamental understanding of the processes that control greenhouse gas fluxes from northern ecosystems. Because wintertime processes are not well understood, these data will be very useful for understanding annual rates of greenhouse gas fluxes. Also, it will be useful to understand and model how processes occurring in different ecosystems that have different rates of thaw, or amount of snow cover, or soil chemistry may impact greenhouse gas production and therefore carbon budgets. By improving our understanding of the wintertime processes, permafrost change, and the fundamental processes that govern carbon storage and release from soils, we can improve predictions of the permafrost carbon feedback and future changes in ecosystems.

Our work and involvement with national and international scientists and agencies is very important. It helps us create products and models that allow scientists to be able to understand and forecast changes at global scales. Some of these collaborations include work with the International Soil Carbon Network, the Permafrost Carbon Network, the Long-Term Ecological Research Network, USGS Climate Adaptation Science Centers, the North American Carbon Program, the International Permafrost Association, the U.S. Department of Agriculture, and NASA.

Objective(s): Our primary objectives are to quantify the sources of winter greenhouse gas fluxes in locations that have minimal permafrost thaw and sites that have extensive permafrost thaw. As such we plan to understand rates of microbial activities and rates of gas diffusion through different zones of the soils (active layer, talik, and permafrost) from different landscape settings. We also propose to understand how differences in flux rates between different aged permafrost soils may be due to differences in the chemistry or microbiology of permafrost soils.

scientists collecting permafrost cores — USGS researchers Jack McFarland and Kristen Manies taking permafrost cores to study the carbon cycle in Interior Alaska.

sampling a permafrost core — Aseptic sampling of a permafrost core for DNA analysis.

Methods: Our work will be conducted at several locations near Fairbanks, Alaska. Foremost is a site called the Alaska Peatland Experiment (APEX), where shallow (< 3 m deep) permafrost is near 0 ⁰C and has warmed over the recent decade producing active layer deepening greater than 50 cm. APEX has been well-characterized with flux towers, autochambers, soil temperature and moisture records, as well as with multiple geophysical methods. At this site, we have employed electrical resistivity tomography (ERT), nuclear magnetic resonance (NMR), and passive seismic techniques to provide insights into spatial and temporal patterns of ice and water within the near surface soil profile, established multiple systems for winter GHG flux monitoring, and established methodologies to examine microbial activities within frozen permafrost soils. Other sites to be included are located near Smith Lake and Goldstream Valley, AK. These sites will allow us to conduct gas diffusion experiments through permafrost, and compare young permafrost at APEX to older permafrost from the Goldstream Valley.