Anthropogenic\nPerchlorate Increases since 1980 in\nthe Canadian High Arctic
Bibliographic record
Abstract
An ice core of 15.5 m retrieved from\nAgassiz Ice Cap (Nunavut,\nCanada) in April 2009 was analyzed for perchlorate to obtain a temporal\ntrend in the recent decades and to better understand the factors affecting\nHigh Arctic deposition. The continuous record dated from 1936 to 2007,\ncovers the periods prior to and during the major atmospheric releases\nof organic chlorine species that affected the stratospheric ozone\nlevels. Concentrations and yearly fluxes of perchlorate and chloride\nshowed a significant correlation for the 1940–1959 period,\nsuggesting a predominant tropospheric formation by lightning. While\nconcentration of chloride remained unchanged from 1940s until 2009,\nelevated levels of perchlorate were observed after 1979. A lack of\nsignificant increases in either sulfate or chloride between 1980 and\n2001 suggests that the effect of volcanic activities on the perchlorate\nat the study site during this period could be insignificant. Therefore,\nthe elevated perchlorate in the ice could most likely be attributed\nto anthropogenic activities that influenced perchlorate sources and\nformation mechanisms after 1979. Our results show that anthropogenic\ncontribution could be responsible for 66% of perchlorate found in\nthe ice. Although with some differences in trends and amounts, deposition\nrate found in this study is similar to those observed at Devon Island\n(Nunavut, Canada), Eclipse Icefield (Yukon, Canada) and Summit Station\n(Greenland). Methyl chloroform, a chlorinated solvent largely used\nafter 1976, peaked in the atmosphere in 1990 and has a much shorter\natmospheric life than chlorofluorocarbons (CFCs). This study proposes\nmethyl chloroform (CH<sub>3</sub>CCl<sub>3</sub>) as the significant\nanthropogenic source of perchlorate in the Canadian High Arctic between\n1980 and 2000, with HCFC-141b (Cl<sub>2</sub>FC–CH<sub>3</sub>), a relatively short-lived CFC probably responsible for a slower\ndecrease in perchlorate deposition after the late 1990s. The presence\nof aerosols in the stratosphere appears to suppress perchlorate production\nafter 1974. As both methyl chloroform and HCFC-141b had no new significant\nemissions after 2003, deposition of perchlorate in High Arctic is\nexpected to remain at pre-1980 levels.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.672 | 0.030 |
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".