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1. Iron Oxidation–Reduction Processes in Warming Permafrost Soils and Surface Waters Expose a Seasonally Rusting Arctic Watershed

   https://doi.org/10.1021/acsearthspacechem.2c00367  

   Barker, Amanda J. ; Sullivan, Taylor D. ; Baxter, W. Brad ; Barbato, Robyn A. ; Gallaher, Shawn ; Patton, Grace E. ; Smith, Joseph P. ; Douglas, Thomas A. ( July 2023 , ACS Earth and Space Chemistry)
2. Microbial iron cycling during palsa hillslope collapse promotes greenhouse gas emissions before complete permafrost thaw

   https://doi.org/10.1038/s43247-022-00407-8  

   Patzner, Monique S. ; Logan, Merritt ; McKenna, Amy M. ; Young, Robert B. ; Zhou, Zhe ; Joss, Hanna ; Mueller, Carsten W. ; Hoeschen, Carmen ; Scholten, Thomas ; Straub, Daniel ; et al ( April 2022 , Communications Earth & Environment)

   Reductive dissolution during permafrost thaw releases iron-bound organic carbon to porewaters, rendering previously stable carbon vulnerable to microbial decomposition and subsequent release to the atmosphere. How mineral iron stability and the microbial processes influencing mineral dissolution vary during transitional permafrost thaw are poorly understood, yet have important implications for carbon cycling and emissions. Here we determine the reactive mineral iron and associated organic carbon content of core extracts and porewaters along thaw gradients in a permafrost peatland in Abisko, Sweden. We find that iron mineral dissolution by fermentative and dissimilatory iron(III) reduction releases aqueous Fe²⁺and aliphatic organic compounds along collapsing palsa hillslopes. Microbial community analysis and carbon emission measurements indicate that this release is accompanied by an increase in hydrogenotrophic methanogen abundance and methane emissions at the collapsing front. Our findings suggest that dissolution of reactive iron minerals contributes to carbon dioxide and methane production and emission, even before complete permafrost thaw.

    

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3. Genomic evidence that microbial carbon degradation is dominated by iron redox metabolism in thawing permafrost

   https://doi.org/10.1038/s43705-023-00326-5  

   Romanowicz, Karl J. ; Crump, Byron C. ; Kling, George W. ( November 2023 , ISME Communications)

   Microorganisms drive many aspects of organic carbon cycling in thawing permafrost soils, but the compositional trajectory of the post-thaw microbiome and its metabolic activity remain uncertain, which limits our ability to predict permafrost–climate feedbacks in a warming world. Using quantitative metabarcoding and metagenomic sequencing, we determined relative and absolute changes in microbiome composition and functional gene abundance during thaw incubations of wet sedge tundra collected from northern Alaska, USA. Organic soils from the tundra active-layer (0–50 cm), transition-zone (50–70 cm), and permafrost (70+ cm) depths were incubated under reducing conditions at 4 °C for 30 days to mimic an extended thaw duration. Following extended thaw, we found that iron (Fe)-cycling Gammaproteobacteria, specifically the heterotrophic Fe(III)-reducing Rhodoferax sp. and chemoautotrophic Fe(II)-oxidizing Gallionella sp., increased by 3–5 orders of magnitude in absolute abundance within the transition-zone and permafrost microbiomes, accounting for 65% of community abundance. We also found that the abundance of genes for Fe(III) reduction (e.g., MtrE) and Fe(II) oxidation (e.g., Cyc1) increased concurrently with genes for benzoate degradation and pyruvate metabolism, in which pyruvate is used to generate acetate that can be oxidized, along with benzoate, to CO2 when coupled with Fe(III) reduction. Gene abundance for CH4 metabolism decreased following extended thaw, suggesting dissimilatory Fe(III) reduction suppresses acetoclastic methanogenesis under reducing conditions. Our genomic evidence indicates that microbial carbon degradation is dominated by iron redox metabolism via an increase in gene abundance associated with Fe(III) reduction and Fe(II) oxidation during initial permafrost thaw, likely increasing microbial respiration while suppressing methanogenesis in wet sedge tundra.

    

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4. Multi-temporal elevation data, ground temperature time-series, and permafrost borehole logs document the recovery of permafrost at the Anaktuvuk River tundra fire, 2009 to 2023

   https://doi.org/10.18739/A2251FM9P  

   Jones, Benjamin ; Kanevskiy, Mikhail ; Shur, Yuri ; Ward Jones, Melissa ; Gaglioti, Benjamin ; Jorgenson, Torre ; Veremeeva, Alexandra ; Miller, Eric ; Jandt, Randi ( January 2024 , NSF Arctic Data Center)

   ### Access Photos of ~50 permaforst boreholes and associated cores can be accessed and downloaded from the 'AR\_Fire\_Core_Photos' directory via: [https://arcticdata.io/data/10.18739/A2251FM9P/](https://arcticdata.io/data/10.18739/A2251FM9P/) ### Overview The Anaktuvuk River tundra fire burned more than 1,000 square kilometers of permafrost-affected arctic tundra in northern Alaska in 2007. The fire is the largest historical recorded tundra fire on the North Slope of Alaska. Fifty percent of the burn area is underlain by Yedoma permafrost that is characterized by extremely high ground-ice content of organic-rich, silty buried soils and the occurrence of large, syngenetic polygonal ice wedges. Given the high ground-ice content of this terrain, Yedoma is thought to be among the most vulnerable to fire-induced thermokarst in the Arctic. With this dataset, we update observations on near-surface permafrost in the Anaktuvuk River tundra fire burn area from 2009 to 2023 using repeat airborne LiDAR-derived elevation data, ground temperature measurements, and cryostratigraphic studies. We have provided all of the data that has gone into an analysis and resulting paper that has been submitted for peer review at the journal Scientific Reports. The datasets include: - 1 m spatial resolution airborne LiDAR-derived digital terrain models from the summers of 2009, 2014, and 2021. - The area in which thaw subsidence was detected in the multi-temporal LiDAR data using the Geomorphic Change Detection software. - A terrain unit map developed for the 50 square kilometer study area. - Ground temperature time series measurements for a logger located in the burned area and a logger located in an unburned area. The ground temperature data consist of daily mean measurements at a depth of 0.15 m (active layer) and 1.00 m (permafrost) from July 2009 to August 2023. - Photos ~50 permafrost boreholes and the associated cores collected there. - A borehole log and notes pdf also accompanies our studies on the cryostratigraphy of permafrost post-fire and our observations on the recovery of permafrost. 

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5. Modeling Long-Term Permafrost Degradation: HOW FAST PERMAFROST CAN THAW?

   https://doi.org/10.1029/2018JF004655  

   Nicolsky, D. J. ; Romanovsky, V. E. ( June 2018 , Journal of Geophysical Research: Earth Surface)

   Permafrost, as an important part of the Cryosphere, has been strongly affected by climate warming, and a wide spread of permafrost responses to the warming is currently observed. In particular, at some locations rather slow rates of permafrost degradations are noticed. We related this behavior to the presence of unfrozen water in frozen fine‐grained earth material. In this paper, we examine not‐very‐commonly‐discussed heat flux from the ground surface into the permafrost and consequently discuss implications of the presence of unfrozen liquid water on long‐term thawing of permafrost. We conducted a series of numerical experiments and demonstrated that the presence of fine‐grained material with substantial unfrozen liquid water content at below 0°C temperature can significantly slow down the thawing rate and hence can increase resilience of permafrost to the warming events. This effect is highly nonlinear, and a difference between the rates of thawing in fine‐ and coarse‐grained materials is more drastic for lower values of heat flux incoming into permafrost. For high heat flux, the difference between these rates almost disappears. As near‐surface permafrost temperature increases towards 0°C and the changes in the ground temperature become less evident, the future observation networks should try to incorporate measurements of unfrozen liquid water content in the near‐surface permafrost and heat flux into permafrost in addition to the existing temperature observations. 

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