Deposition of Polychlorinated Biphenyls to Firn and Ice Cores at Opposite Polar Sites: Site M, Dronning Maud Land, Antarctica, and Holtedahlfonna, Svalbard
Bibliographic record
Abstract
Firn and ice cores from glaciers and ice sheets at polar opposite locations, Site M, Dronning Maud Land, East Antarctica (lat 75.00 S, long. 15.00 E), and Holtedahlfonna, Svalbard (lat 79.13 N, long. 13.27 E), were analyzed for 81 polychlorinated biphenyl (PCB) congeners in 75 chromatographic peaks. Both sites are remote at high elevations and receive contaminant inputs from long-range atmospheric transport (LRAT). Firn cores from Site M formed one sample covering 1958–2000, while the Holtedahlfonna site has a historic record in 6 samples from 1953 to 2005. Most congeners at both sites are in triCB, tetraCB, and pentaCB homologs, and at Site M, these comprise 89% of PCB and 83% at Holtedahlfonna (with variability over time). Site M PCBs are dominated by pentaCB (48%), while Holtedahlfonna (whole-core average) is dominated by tetraCB (45%). The dominant congeners in triCB through hexaCB homologs are the same at both sites (PCB-28 + 31, PCB-70, PCB-101, PCB-138). The total PCB flux at Site M (4.1 pg cm –2 yr –1 ) was ∼33% of Holtedahlfonna (12.7 pg cm –2 yr – 1) over whole-core history, perhaps resulting from high UV during spring Antarctic stratospheric ozone depletion leading to PCB decomposition. LRAT frequency diagrams showed a limited range of sources to Site M, leading to a hypothesis about transport through the stratosphere. The LRAT diagram for Holtedahlfonna shows greater than 1% time-coverage areas through central and northern Europe and Russia over 52 years. There is no apparent quantitative trend to PCB deposition over time at Holtedahlfonna, similar to observations elsewhere in the Arctic.
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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 | 0.001 | 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".