Hg isotope fractionation in sediment cores
Bibliographic record
Abstract
Analytical advances in the past decade and the recent advent of multicollector inductively coupled plasma mass spectrometry (MC-ICP/MS) have made it possible to measure fractionation of non-traditional elements such as mercury. We measured the isotope fractionation of mercury in different sediment cores to establish historical records. Marine sediment profiles from deep Pacific locations and from remote lakes on Vancouver Island (British Columbia) and the Experimental Lakes Area (Ontario) were investigated. While the Pacific and Ontario cores (going back to approx. 1800) compare well with each other in that older sediments become progressively enriched with lighter Hg isotopes, the much older BC records (dating back to ca.8000 BC) show the opposite trend starting at around 500 AD increasing in the bottom layers. Only a small degree of mass independent fractionation was detected in this study. While most samples contained sufficient mercury for the measurement, some were as low as 5 ng/g and required preconcentration prior to the isotope ratio measurement. Nitric acid/sulfuric acid sediment digests were evaporated to near dryness and re-dissolved in max. 20 % acid. delta-202Hg before and after pre-concentration were statistically not different from each other, demonstrating that this preconcentration process does not fractionate Hg isotopes.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.001 | 0.005 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 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 teacher head, 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".