Climate change and recent sedimentation in Nastapoka Sound, eastern coast of Hudson Bay
Bibliographic record
Abstract
In an attempt to determine to what extent the impact of recent climate changes that occurred east of Hudson Bay, including important reduction of areas in permafrost, had on the coastal marine environment, a series of shallow cores were extracted from the seabed off the mouth of the Sheldrake River, in Nastapoka Sound. A total of 25 cores were taken in April 2009 from the ice cover. A preliminary seafloor map was first done to help in the selection of the coring sites. Nastapoka Sound has a complex subaqueous relief, formed of asymmetric ridges and deep basins. After preliminary sedimentological analyses, six of the cores were selected for physical and chronological analyses (14C, 210Pb, and 137Cs dating); among them, three were selected for elemental (C, N, OC/TN) and isotopic (δ13C, δ15N) analyses to identify sedimentary organic matter sources. Sedimentation processes are complex and are primarily driven by bottom currents. This is confirmed by the absence of a clay fraction in several cores, some erosion surfaces in a few cores, and the presence of comet-like mark features on the seafloor. The highest sedimentation rates are found near the coast of the province of Quebec and Gillies Island and the lowest ones occur in the deep depocenters. Isotopic and elemental analyses reveal that Nastapoka Sound is an area of mixing between marine and terrestrial inputs and can be compared to an estuarine system similar to nearby Lac Guillaume-Delisle. Those conditions altogether make it difficult to extract a perfectly clear signal of climate change in the recent sediment record. However, the downcore application of a simple two end-member mixing model to measured δ13C values strongly suggests that the fraction of sedimentary organic matter from terrestrial sources increased by 30% since about the middle of the Little Ice Age. This trend accelerated at the end of the 20th century. Rapid permafrost decay in adjacent river catchments is likely one source for this terrestrial carbon. However, it cannot be distinguished from other potential sources that are also related to environmental changes such as increase in primary productivity both on land, where peatlands, shrubs, and forest are expanding, and at sea, where sea ice cover duration is diminishing.
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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 | 0.001 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".