Seasonal fluctuations of the rusty carbon sink in thawing permafrost peatlands
Bibliographic record
Abstract
In permafrost peatlands, up to 20% of total organic carbon (OC) is bound to reactive iron (Fe) minerals in the active layer overlying intact permafrost, potentially protecting OC from microbial degradation and transformation into greenhouse gases (GHG) such as CO2 and CH4. During the summer, shifts in runoff and soil moisture influence redox conditions and therefore the balance of Fe oxidation and reduction. Whether this “rusty carbon sink” is stable or continuously dissolved by Fe(III) reduction and reformed by Fe(II) oxidation during redox shifts remains unknown. We exposed ferrihydrite (FH)-coated sand in the active layer along a permafrost thaw gradient in Stordalen mire (Abisko, Sweden) over the summer (June to September) to capture changes in redox conditions and quantify formation and dissolution of reactive Fe(III) (oxyhydr)oxides and associated OC. We found that Fe(III) minerals formed under the constantly oxic conditions in palsa soils overlying intact permafrost over the full summer season. In contrast, in fully-thawed fen areas, conditions were continuously anoxic and by late summer 50.4% of the original Fe(III) (oxyhydr)oxides were lost via dissolution while 44.7% and 4.9% of the Fe remained as Fe(III) and Fe(II) on the sand, respectively. Periodic redox shifts (from 0 mV to +300 mV) were observed over the summer season in the partially-thawed bog due to changes in active layer depth, runoff and soil moisture. This resulted in dissolution and loss of 47.5% of initial Fe(III) (oxyhydr)oxides and release of associated OC in early summer when conditions are wetter and more reduced, and new formation of Fe(III) minerals (34.7% gain in comparison to initial Fe) in the late summer under more dry and oxic conditions which again sequestered Fe-bound organic carbon. Our data suggests that the so-called rusty carbon sink is seasonally dynamic in partially-thawed permafrost peatlands, thus likely either promoting or suppressing carbon mineralization and leading to seasonal changes in GHG emissions.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".