Sources of mercury in deep-sea sediments of the Mediterranean Sea as revealed by mercury stable isotopes
Bibliographic record
Abstract
Abstract Mercury (Hg) and its stable isotope composition were used to determine the sources of Hg in deep-sea sediments of the Mediterranean Sea. Surface and down-core sediment δ202Hg values varied widely between −2.30 and +0.78‰, showed consistently positive values for mass independent fractionation of odd Hg isotopes (with average values of Δ199Hg = +0.10 ± 0.04‰ and Δ201Hg = +0.04 ± 0.02‰) and near-zero Δ200Hg values, indicating either multiple Hg sources or a combination of different Hg isotope fractionating processes before and after sediment deposition. Both mass-dependent and mass-independent fractionation processes influence the isotopic composition of Hg in the Mediterranean Sea. Positive Δ199Hg values are likely the result of enhanced Hg2+ photoreduction in the Mediterranean water column before incorporation of Hg into sediments, while mass-dependent fractionation decreases δ202Hg values due to kinetic isotope fractionation during deposition and mobilization. An isotope mixing model based on mass-dependent and mass-independent fractionation (δ202Hg and Δ199Hg) suggests at least three primary Hg sources of atmospheric deposition in the surface sediments: urban, industrial and global precipitation-derived. Industry is the main source of Hg in Algerian and Western Basin surface sediments and at two sites in the Adriatic Sea, while the urban contribution is most prominent at the Strait of Otranto (MS3) and in Adriatic surface sediments. The contribution from precipitation ranged from 10% in Algerian to 37% in W Basin sediments. Overall, results suggest that atmospheric Hg deposition to Mediterranean surface sediments is dominated by gaseous elemental mercury (58 ± 11%) rather than wet deposition.
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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) | 0.000 | 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".