Atmospheric mercury deposition in alpine snow, northern British Columbia and southwestern Yukon, Canada
Bibliographic record
Abstract
High mercury (Hg) levels have been measured in fish in Kusawa Lake (KL), a subalpine, partly glacier-fed lake situated in the southwestern Yukon, Canada, but it is presently unknown where this Hg comes from. One possible source may be atmospheric deposition of Hg in snow and subsequent release by melt into the lake. In this study, the amounts of total Hg (THg) deposited in sampled alpine snow and glacial ice from the KL catchment area were measured in order to quantify this input. Samples of snow and glacial firn were also collected from another site (DIV) located on an icefield in the central St. Elias Mountains, to investigate possible spatial variations in Hg deposition as a function of altitude or distance from the Pacific Ocean. The samples were analysed for THg, major ions (incl. Ca2+, K+, Mg2+, Na+, NH4+, Cl-, and SO42-) and stable O/H isotopes. These analyses were performed to obtain clues on the sources/conditions of atmospheric Hg deposition in snow, and identify possible relationships between THg and other snow chemical properties. This is the first study to provide data on Hg deposition in snow from this vast mountain region. Measured THg concentrations ranged from 0.24 to 6.17 ng L-1 in snow and from 0.20 to 1.57 ng L-1 in glacial ice, which are comparable values to those measured at other sites in the North American subarctic and Arctic. The calculated net accumulation rates of THg varied from 0.57 to 0.71 µg m-2 a-1, which are relatively high compared to rates reported for the eastern Canadian Arctic. This could indicate that wet deposition in snowfall may be particularly important in promoting THg accumulation in mountains of the subarctic Yukon, when compared to the polar desert of the High Arctic. The stable O/H isotope data indicate that snowfall in the study area is primarily derived from moisture of marine origin, with only minor continental contributions, which points to the nearby Gulf of Alaska as the main source. The major ion analyses suggest a local dust source containing Ca2+ and SO42- at KL, and a local dust source containing mostly Mg2+ and Ca2+ but also SO42- at DIV. High correlation between NO3- and SO42- in snow could be due to distant pollution sources, and higher concentrations at DIV than KL could indicate a higher impact of these sources at higher-altitude sites. High correlation was found among the analysed sea salt ions at both sites. No correlations were found between THg and major ions, except that relatively high THg and ionic concentrations were often found in the surface and bottom samples of the snowpits, which correspond to the current and previous summer surfaces. The higher THg concentrations in the summer layers suggests that Hg attaches itself to dust particles either in the air prior to deposition, and/or in the snowpack after deposition, thereby limiting migration or losses in percolating meltwater.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| 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 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".