Pliocene climate change on Ellesmere Island, Canada : annual variability determined from stable isotopes of fossil wood
Bibliographic record
Abstract
Tree-ring analyses have contributed significantly to investigations of climate change and climate cycles, including the North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO) and El Niño/Southern Oscillation (ENSO). Stable isotope climate proxies (?18O, ?D, and ?13C) have enhanced traditional ring-width data, although poor preservation of ancient wood has generally constrained reconstruction of stable isotope proxy records to the Holocene and Late Pleistocene. An opportunity to apply these stable isotope methods to older wood has been presented by recovery of remains of Mixed-Coniferous Boreal Vegetation, in Early Pliocene (4-5 Ma) deposits at Strathcona Fiord, Ellesmere Island, Canada (~79°N). An exceptionally well-preserved tree trunk, identified as Larix (larch) through wood anatomical characteristics, from this high Arctic site provided a 203-year tree-ring record, from which we present the first high-resolution, secular isotope record of Pliocene climate. ?18O, ?D, and ?13C isotope values indicate a variable climate with alternating intervals of cool/wet to warm/dry weather. These fluctuations in climate may be attributable to phase changes in climate cycles observed in the record. A growing season mean temperature of 14.4 °C was calculated from isotopic analysis of gastropod shells. Palaeoclimatic modeling of tree isotope values has revealed growing season temperatures of 11-15 °C, and estimated isotope values of precipitation of –18.3 ‰ (?18O) and –228 ‰ (?D). Both palaeotemperature estimates and source water calculations are comparable to those found in a modern Boreal Forest. Time-series wavelet analysis was applied to these data revealing prominent short (
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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 | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".