Early Holocene marine incursion and a freshened Tyrrell Sea in Hudson Bay Lowlands, Canada
Bibliographic record
Abstract
The Tyrrell Sea developed in the Hudson Bay Lowlands after the breakup of the ice saddle of the Laurentide Ice Sheet over Hudson Bay in the early Holocene. Coeval with its incursion was the final drainage of glacial Lake Agassiz-Ojibway which many hypothesize freshened the North Atlantic, causing significant cooling at 8.2 ka. However, little is known about the freshening of this inland sea itself. This paper presents our study of the sedimentology and stable isotope geochemistry on the extensively exposed Tyrrell Sea deposit in the open pit of the former Victor diamond mine near the Attawapiskat River. The sediment succession indicates that the ice saddle covered the study area prior to its breakup and the final drainage of Lake Agassiz-Ojibway, differing from previous interpretations that placed this site in the lake about 135 km south of the ice margin. Oxygen isotope data from benthic foraminifera ( Haynesina orbicularis ) indicate that the drainage of Lake Agassiz-Ojibway freshened the Tyrrell Sea with low δ 18 O (1.18‰ VPDB) for a short period from 8.1 ± 0.3 to 8.07 ± 0.3 cal ka BP. After regaining its original isotope composition with elevated δ 18 O (1.7–2.2‰) at 8.07 ± 0.3 to 7.8 ± 0.2 cal ka BP, the sea underwent a major freshening for more than a millennium at 7.8 ± 0.2 to 6.6 ± 0.2 cal ka BP, whereby δ 18 O was lowest (0.36–1.15‰). This millennial-scale freshening occurred during the accelerated recession of the ice sheet as previous 10 Be dating work indicates and likely resulted from large meltwater influx from the ice. Subsequent reduction in meltwater influx slowed ocean freshening and raised δ 18 O slightly (0.73–0.83‰) until the Tyrrell Sea withdrew from this site around 6.1 ± 0.5 cal ka BP. Although the initial, short-lived freshening agrees in chronology with the 8.2 ka cooling, the later, millennial-scale freshening has no corresponding oxygen isotope and climate anomalies in the Labrador Sea sediment and Greenland ice cores, respectively. This inconsistency casts doubts on the concept that the brief freshening of the North Atlantic by the drainage of Lake Agassiz-Ojibway could have caused the cooling. • Drainage of Lake Agassiz-Ojibway briefly freshened the Tyrrell Sea around 8.1 cal ka. • Tyrrell Sea underwent a millennial-scale freshening at 7.8–6.6 cal ka. • The causal link between the lake drainage and 8.2 ka cooling is questioned.
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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 | 0.002 | 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 | 0.000 |
| 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 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".