Tweedsmuir Glacier, Alsek River, and the salmon migration that wasn’t
Bibliographic record
Abstract
Sockeye salmon are an important species both ecologically as well as culturally. At some point in the recent geological past, as substantiated by Indigenous oral history and ecological data, sockeye would migrate up Alsek River through the St Elias Mountains into southwest Yukon. But they no longer do so, and river-blocking surges of Nàłùdäy (Lowell Glacier), which translates to ‘Fish Stop’, have been blamed. During multiple surges over the past few thousand years, Nàłùdäy impounded massive glacial lakes, which drained catastrophically and transported vast quantities of gravel and boulders downstream. Although Nàłùdäy has not blocked Alsek River since the late 1800s, sockeye have yet to recolonize this stretch of the river. In this study, we suggest a recent advance of Tweedsmuir Glacier, about 65 km downstream of Nàłùdäy, caused Alsek River to carve the narrow Turnback Canyon into bedrock. This canyon, which stretches for ~10 km along the glacier’s terminus and in places is only a few metres wide, produces a functionally insurmountable velocity barrier to upstream fish migration. The ultimate goal of the study is to determine whether Alsek River was rerouted in the recent geological past, cutting off the sockeye salmon migration. Our specific objectives are to (1) determine whether an ancestral paleochannel of Alsek River exists beneath Tweedsmuir Glacier; (2) establish the chronology of canyon incision and determine whether it was related to rapid drainage of ice-dammed lakes at Nàłùdäy; and (3) evaluate whether the subglacial topography may be conducive to Alsek River abandoning Turnback Canyon as the glacier retreats, creating a gentler stretch of river allowing fish to reach upstream habitat. Between 2019 and 2022, we collected more than 450 line-km of airborne and ground-based ice-penetrating radar data over the lower glacier to map the subglacial topography with the intent of determining whether a paleochannel might exist up which sockeye may have traveled prior to Neoglacial advances. Results suggest that the terminal lobe of Tweedsmuir Glacier is up to ~500 m thick and in some places the bed is up to ~100 m below sea level. Based on preliminary analyses of the radar data, it is conceivable that Alsek River could abandon Turnback Canyon for the lower elevation terrain, as the glacier retreats in the coming decades and centuries. Terrestrial cosmogenic nuclide dating of the canyon walls using 36Cl suggests that the canyon was cut within the last thousand years, and very quickly, possibly in a single episode of downcutting.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 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".