Multiple geochronological approaches to constrain late Quaternary glacial histories in western Canada
Bibliographic record
Abstract
My dissertation investigates late Pleistocene and Holocene glacier change in western Canada and is presented in five chapters. In chapter one, I discuss the importance of the cryosphere, the techniques used for reconstructing past glacier behavior, previous research that has contributed to our current understanding of past glacier change, and the objectives and structure of my dissertation. In chapter two, I complete a multi-proxy investigation of Holocene glacier change at Gilbert Glacier, in the Southern Coast mountains. I use radiocarbon dating of lateral moraine stratigraphy and cosmogenic nuclide surface exposure dating to constrain the timing and duration of late Holocene advances at Gilbert Glacier to 2.0–1.8, ~1.5–1.3, ~0.9–0.8, and 0.4–0.1 ka. Organic matter associated with glacier advance within the north-lateral moraine at Gilbert Glacier records advances at 4.8–4.6, 4.5–4.3, 4.0–3.9, 3.8–3.6, 3.4, 3.2–2.9, 2.7, and 0.5–0.3 kilo calendar years BP (ka; 2-sigma age range). I advocate for the tandem use of multiple glacial geochronologic tools to better constrain the onset and termination of glacier advances. Chapter three applies cosmogenic surface exposure dating to a previously understudied region in the Mackenzie and Selwyn mountains of the eastern Yukon and Northwest Territories to develop a late Holocene glacier chronology. Surface exposure ages from 27 moraine boulders across nine glaciers show that glaciers reached their greatest Holocene extent between 1600-1850 CE. I use this glacier chronology to tune a glacier model forced by models of past climate to estimate regional changes in ice volume over the past millennium. Additionally, I use the same glacier model to estimate that glaciers in the region will decline in ice volume by 85% - 97% by 2100 CE. Chapter four returns to the southern Coast mountains where I use cosmogenic dating on moraine boulders, bedrock surfaces, and shallow bedrock cores to investigate the history of deglaciation and Holocene glacier behavior of a small cirque glacier. Bedrock surfaces within and outside of the late Holocene maximum extent of the glacier record complex burial and exposure histories. I employ a Monte Carlo approach to evaluate the most likely glacier history that can be explained by our data. I discuss how our results compare with the work of previous chapters and past research, and the limitations of this technique to constrain the many variables that impact surface exposure ages. Chapter five provides a summary of my study’s major findings and further discusses their limitations and broader implications. I conclude with recommendations for future research that will expand on the work presented in this dissertation.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.004 | 0.006 |
| Science and technology studies | 0.002 | 0.000 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".