Tracking permafrost thaw using iron as a geochemical tracer for climate change

Arctic ecosystems are changing as a result of climate warming, altering soil thermal and moisture regimes and contributing to permafrost thaw, which impacts the biogeochemistry of terrestrial and aquatic environments. This occurs across broad scales of space and time. Assessing how and to what extent thawing permafrost impacts soils, sediments, and aquatic environments is integral to constraining greenhouse gas emission estimates, microbial diversity, vegetation succession, and water quality, but quantifications remain difficult to assess on a landscape-scale. When top-down thaw of near-surface permafrost occurs porewaters infiltrate deeper and expose fresh, previously frozen material. This input of oxygenated water greatly alters the oxidation/reduction (redox) conditions, which are intricately tied to soil moisture/temperature, ionic strength, and play a critical role in carbon release. Using optical sensors, satellite and unmanned aerial surveys, and bulk- and micro-scale analytical techniques, we present a comprehensive approach for tracking iron concentrations and redox conditions in permafrost regimes in the Arctic. Overall, we found evidence that iron (Fe) and to a lesser extent manganese (Mn) could be useful as geochemical indicators of permafrost thaw and release of Fe(II) from thawing permafrost and further oxidation to Fe(III) could translate to a higher degree of seasonal rusting coinciding with the warming and thawing of near surface-permafrost.