PAH Fluxes to Siskiwit Revisted: Trends in Fluxes and Sources of Pyrogenic PAH and Perylene Constrained via Radiocarbon Analysis
Bibliographic record
Abstract
Trends in concentrations and radiocarbon content of pyrogenic PAHs and perylene were determined 20 years after a previous study by Mcveety and Hites (1988). Pyrogenic PAH fluxes to sediments were observed to continue to decrease over the period from 1980 to 2000 at this remote site in contrast to observations in more urban areas. Radiocarbon analysis of pyrogenic PAHs showed a 50% decrease in the proportion of pyrogenic PAH derived from fossil fuel combustion over the past 50 years, consistent with decreasing emissions from regional coal-fired power-generating plants. Fluxes of pyrogenic PAHs related to biomass burning were consistent over this same period and found to exceed fossil fuel sources in the most recent samples. Fluxes of biomass-derived pyrogenic PAHs were similar in magnitude to total pyrogenic PAH fluxes in early 1900, suggesting that these fluxes may represent wildfire inputs. Not only did perylene concentrations in these sediments increase with depth as previously observed but also concentrations from the same sedimentary layers analyzed 20 years previously showed large increases in perylene concentrations. Radiocarbon analysis of perylene indicated that 70-85% of perylene observed in the deeper sediments could be explained by production from total organic carbon.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".