 Changes in erosion and sediment dynamics in a retreating world: high resolution provenance analysis from detrital apatite
Bibliographic record
Abstract
Glacial retreat quickly and dramatically changes erosion dynamics across catchments. As ice retreats, newly exposed valley walls and sediment can become the target of hillslope and fluvial erosion that in turn can significantly increase sediment fluxes downstream. These increasing fluxes have important implications for hydropower generation and water quality, presenting risks to biodiversity, ecosystem stability, and human inhabitants. Determining where this new influx of sediment is derived from, and hence what parts of catchments are experiencing the greatest erosion, requires the ability to trace exactly where is sediment derived from in the catchment.Recent analytical advances in the dating of apatite have improved its utility as a provenance tool. The advent of LA-ICP-MS techniques now allow thermochronometric, geochronometric, and chemical data to be collected from each individual grains of a detrital sample. As such, we are able to trace sediment sources across a partially glaciated catchment based on lithology, and source-rock elevation. In this work, we collected samples across the Bugaboo Glacier catchment in western Canada, where ice has retreated >2 km in the last century. Detrital samples were collected from the outwash river and two moraine samples, coupled with a bedrock elevation profile. Bedrock samples encompass the catchment’s two principal lithologies, a Cretaceous granitic intrusion, and Neoproterozoic metasediments. Thermochronometric dates range from 41.4 Ma at the highest elevation to 23.9 Ma at the lowest, while geochronometric dates range 68.7–151.3 Ma in granites to 90.5–1952 Ma in metasediments. Supplementary chemical data also help to highlight key differences between the lithologies.Dates and chemistry from moraine samples show they are likely derived primarily from upstream granitic sources, while sample from the modern outwash river suggests a greater mixture of sources. Detrital mixture models and multi-dimensional scaling suggest moraine samples are composed of sediment derived from a wide range of elevations within the catchment, while the sediments of the modern outwash river appear to be derived entirely from erosion of these moraines, left exposed by retreating ice. This suggests the widely documented increase in sediment flux during glacial retreat is primarily driven by the erosion of newly exposed unconsolidated moraines in catchments. Moreover, this work helps to highlight how the analysis of detrital apatite can be harnessed to produce a highly accurate provenance tool in glacial catchments.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".