Bibliographic record
Abstract
Recent climate warming is disproportionately impacting the Arctic. Over the last decades, the Arctic is warming nearly four times faster than the global average. This has a significant local and global impact, for example through thaw and destabilisation of permafrost, the ‘permanently’ frozen ground below the Arctic. Thaw of permafrost reintroduces the soil organic carbon (OC) it holds into the short-term carbon cycle. This OC, when mobilised by thaw and subject to degradation, can be a significant source of greenhouse gases. However, redeposition and storage of permafrost OC in river- and marine sediments can attenuate this ‘permafrost carbon feedback’. It is still poorly understood whether lateral transport of permafrost OC through aquatic systems will strengthen this feedback through degradation of OC along the way, or weaken it through burial of OC in sediments. The objective of this thesis is to assess the fate of permafrost OC in aquatic systems. We will start from the source, and move along the path the permafrost OC takes to its destination in an integrated approach, and assess what is left and what is lost along its journey. We will combine sedimentological (grain size, mineral surface area) and geochemical analyses (elemental C and N, molecular biomarkers, and carbon isotopes δ13C and radiocarbon) on samples from the source (permafrost thaw sites), transitional environments (rivers, thaw slumps, nearshore zone), the marine shelf and marine basins to assess the degradation, deposition, and transport potential of permafrost OC along the land-to-ocean continuum, on both a small scale (5 km, Herschel Island – Herschel Basin, Yukon, Canada) and a large scale transect (1500 km, Kolyma River – East Siberian Sea, North East Siberia, Russia). This thesis highlights that every pool of OC needs to be included when studying the pathway and destination of permafrost OC on a land-ocean transect: dissolved in water (DOC), as particulate matter (POC), and within the soil and sediments (SOC). This type of integrated carbon cycle-approach is necessary for both river and marine studies, where we should consider that each pool of permafrost OC is ‘processed’ at a different stage along its journey, and acknowledge the complex and dynamic interactions between different carbon pools along the way. We find that the transitional zones play a crucial role for processing permafrost OC: particularly the zone between ‘undisturbed’ permafrost and ‘thaw-mobilised’ permafrost material (e.g. the thaw slumps, thaw streams, mudpools), and the zone on the border of land and ocean, (e.g. the nearshore zone for coastal erosion or the delta for larger rivers). Furthermore, we find that the combination of biogeochemical and sedimentological methods is especially necessary when comparing samples from different sedimentary environments, and recommend further integration of these methods. Sorting of OC during transport through deposition and resuspension, and the affinity of certain types of OC to mineral particles through adsorption and desorption can affect biomarker proxies for degradation just as well as actual degradation.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.003 | 0.002 |
| Scholarly communication | 0.003 | 0.002 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.006 | 0.001 |
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".