Fate of organic matter mobilized from eroding permafrost coasts
Bibliographic record
Abstract
Permafrost, defined as ground that remains frozen for at least two consecutive years, is a prominent feature of polar regions. In the Northern Hemisphere, approximately 23 million km2 of the ground are affected by permafrost. Climatic warming, which has a greater effect on the Arctic than on any other region on Earth, leads to permafrost thaw, caused by gradual deepening of the seasonal unfrozen layer (active layer), thermokarst formation (i.e. land subsidence due to ground ice loss) and thermo-erosion. In the course of thaw, formerly freeze-locked organic carbon (OC) is mobilized and mineralized into greenhouse gases (GHGs), fostering further climate warming – a process known as permafrost carbon feedback. Current climate models focus on GHG release from gradual deepening of the active layer and neglect the OC turnover during lateral transport induced by thermokarst and abrupt thermo-erosion. As such, the accelerated erosion of Arctic permafrost coasts, which make up ~34 % of the global coasts, deliver vast amounts of OC into the Arctic Ocean. However, little is known about the amounts of labile and fast bioavailable dissolved OC (DOC), the impact of thermokarst on mobilized organic matter (OM) characteristics, and the release of GHGs from eroding permafrost coasts. To fill that knowledge gap, the main objectives of the thesis are to investigate (i) how much DOC is mobilized from coastal erosion, (ii) how thermokarst and -erosion alters OM characteristics upon thaw on transit to the ocean, and (iii) how much GHGs are emitted from the nearshore zones of eroding permafrost coasts. Field work and sampling took place along the Yukon coast and on Qikiqtaruk (Herschel Island) in the western Canadian Arctic. An interdisciplinary approach was used to quantify OM (OC and nitrogen) as well as to identify degradation processes. The methods used included sedimentology, geo- and hydrochemistry, remote sensing, statistical analyses, and gas chromatography. The thesis shows that considerable amounts of DOC are released from eroding permafrost coasts. Although OC fluxes into the ocean are dominated by DOC from Arctic rivers and particulate OC (POC), labile DOC derived from permafrost plays an important role as it is quickly available for biogeochemical cycling and turnover into GHGs. During transit from land to ocean OM characteristics are substantially altered by thermokarst formation and thermo-erosion. In mudpools, originating from in-situ thawed permafrost, as well as in thaw streams draining thermokarst features towards the ocean, mobilized OM issubject to dilution with melted ground ice and degradation, which result in a decrease of OM contents by more than 50 %. The turnover of OC continues in the nearshore zone. The biochemically most labile OC portions are rapidly lost within months and mineralized into GHGs. The production of GHGs in the ocean is 60 to 80 % as efficient as on land and primarily in form of carbon dioxide (CO2), due to aerobic conditions in the nearshore zone. During each open water season in the Arctic approximately 0.7 to 1.2 Tg of CO2 are emitted from the coastal fringe. The remaining OM is buried in nearshore and shelf sediments, potentially remobilized by waves, currents and ice scouring at later stages. To conclude, the thesis shows that eroding permafrost coasts release large amounts of OC, from which considerable portions are labile DOC. In the course of thermokarst formation and thermo-erosion, OM is diluted and the most labile portions subject to rapid turnover into GHGs. This shows that eroding permafrost coasts are a major yet neglected source of CO2 to the atmosphere. With increasing temperatures and longer sea ice-free conditions projected for the Arctic, the erosion of permafrost coasts accelerates. Consequently, the transfer of OC to the ocean accompanied by GHG production increases, which is expected to have drastic impacts for the climate and coastal ecosystems.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".