HYDROCLIMATE CHANGE IN SOUTHWESTERN BRITISH COLUMBIA, CANADA REVEALED BY A 7000 YEAR LAKE SEDIMENT OXYGEN ISOTOPE RECORD
Bibliographic record
Abstract
Holocene climate variability in the Pacific Northwest has not been well characterized due to the scarcity of continuous, high-resolution records and inconsistencies in proxy sensitivity. Analyses of the oxygen isotopic composition of lake sediment carbonates contribute to this research by providing information on past changes in water isotope values (δ18O), which respond to a variety of climate variables including changes in the balance between precipitation and evaporation, lake level, and/or the isotopic composition of precipitation. Here we present a decadally resolved carbonate oxygen isotope record spanning the last ~7000 yr BP from Turquoise Lake (N50.83°, W121.69°, 807 m), a small, alkaline, semi-closed basin system located in southwestern British Columbia. Turquoise Lake surface water isotope values fall along the local evaporation line but are not substantially enriched relative to local meteoric water, indicating that water losses from the lake occur principally through overflow and groundwater outseepage. We measured the δ18O values of carbonates in three meters of sediment recovered from the depocenter of Turquoise Lake, in order to make inferences on climate change during the Holocene. We dated the Turquoise Lake record using 210Pb, 137Cs, 10 14C measurements, and one tephra layer and analyzed 374 samples of authigenic carbonate (the <63µm fraction) collected at 2 mm intervals. The Turquoise Lake δ18O record exhibits highly positive values at ~7000 years BP, indicating low lake levels and dry conditions at this time, consistent with a similar δ18O record from Castor Lake, WA. δ18O values over the remainder of the Holocene exhibit marked multi-century scale variability, indicating changes in hydroclimate that likely far exceed those observed historically. The Turquoise Lake δ18O results provide insight on the influence of Pacific ocean-atmosphere dynamics including the El Niño Southern Oscillation, Pacific Decadal Oscillation, and the Pacific North American Pattern on climate in the Pacific Northwest, and thus should improve our overall understanding of past hydroclimate changes in North America.
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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 | 0.003 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".