A 1000‐year record of dry conditions in the eastern Canadian prairies reconstructed from oxygen and carbon isotope measurements on Lake Winnipeg sediment organics
Bibliographic record
Abstract
Abstract A short sediment core (162 cm), covering the period AD 920–1999, was sampled from the south basin of Lake Winnipeg for a suite of multi‐proxy analyses leading towards a detailed characterisation of the recent millennial lake environment and hydroclimate of southern Manitoba, Canada. Information on the frequency and duration of major dry periods in southern Manitoba, in light of the changes that are likely to occur as a result of an increasingly warming atmosphere, is of specific interest in this study. Intervals of relatively enriched lake sediment cellulose oxygen isotope values (δ18Ocellulose) were found to occur from AD 1180 to 1230 (error range: AD 1104–1231 to 1160–1280), 1610–1640 (error range: AD 1571–1634 to 1603–1662), 1670–1720 (error range: AD 1643–1697 to 1692–1738) and 1750–1780 (error range: AD 1724–1766 to 1756–1794). Regional water balance, inferred from calculated Lake Winnipeg water oxygen isotope values (δ18Oinf‐lw), suggest that the ratio of lake evaporation to catchment input may have been 25–40% higher during these isotopically distinct periods. Associated with the enriched δ18Ocellulose intervals are some depleted carbon isotope values associated with more abundantly preserved sediment organic matter (δ13COM). These suggest reduced microbial oxidation of terrestrially derived organic matter and/or subdued lake productivity during periods of minimised input of nutrients from the catchment area. With reference to other corroborating evidence, it is suggested that the AD 1180–1230, 1610–1640, 1670–1720 and 1750–1780 intervals represent four distinctly drier periods (droughts) in southern Manitoba, Canada. Additionally, lower‐magnitude and duration dry periods may have also occurred from 1320 to 1340 (error range: AD 1257–1363), 1530–1540 (error range: AD 1490–1565 to 1498–1572) and 1570–1580 (error range: AD 1531–1599 to 1539–1606). Copyright © 2009 John Wiley & Sons, Ltd.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".