Perchlorate\nin The Great Lakes: Isotopic Composition\nand Origin
Bibliographic record
Abstract
Perchlorate\nis a persistent and mobile contaminant in the environment\nwith both natural and anthropogenic sources. Stable isotope ratios\nof oxygen (δ<sup>18</sup>O, Δ<sup>17</sup>O) and chlorine\n(δ<sup>37</sup>Cl) along with the abundance of the radioactive\nisotope <sup>36</sup>Cl were used to trace perchlorate sources and\nbehavior in the Laurentian Great Lakes. These lakes were selected\nfor study as a likely repository of recent atmospheric perchlorate\ndeposition. Perchlorate concentrations in the Great Lakes range from\n0.05 to 0.13 μg per liter. δ<sup>37</sup>Cl values of\nperchlorate from the Great Lakes range from +3.0‰ (Lake Ontario)\nto +4.0‰ (Lake Superior), whereas δ<sup>18</sup>O values\nrange from −4.1‰ (Lake Superior) to +4.0‰ (Lake\nErie). Great Lakes perchlorate has mass-independent oxygen isotopic\nvariations with positive Δ<sup>17</sup>O values (+1.6‰\nto +2.7‰) divided into two distinct groups: Lake Superior (+2.7‰)\nand the other four lakes (∼+1.7‰). The stable isotopic\nresults indicate that perchlorate in the Great Lakes is dominantly\nof natural origin, having isotopic composition resembling that measured\nfor indigenous perchlorate from preindustrial groundwaters of the\nwestern USA. The <sup>36</sup>Cl/Cl ratio of perchlorate varies widely\nfrom 7.4 × 10<sup>–12</sup> (Lake Ontario) to 6.7 ×\n10<sup>–11</sup> (Lake Superior). These <sup>36</sup>ClO<sub>4</sub><sup>–</sup> abundances are consistent with an atmospheric\norigin of perchlorate in the Great Lakes. The relatively high <sup>36</sup>ClO<sub>4</sub><sup>–</sup> abundances in the larger\nlakes (Lakes Superior and Michigan) could be explained by the presence\nof <sup>36</sup>Cl-enriched perchlorate deposited during the period\nof elevated atmospheric <sup>36</sup>Cl activity following thermonuclear\nbomb tests in the Pacific Ocean.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 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) | 0.670 | 0.024 |
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; both teacher heads agree on what is shown here.
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".