Late Cenozoic reconstructions of precipitation isotopes and climate in continental Alaska and Yukon
Bibliographic record
Abstract
This thesis presents late Cenozoic reconstructions of hydrogen isotope ratios in mean annual precipitation (dDMAP) from fossil plant waxes (n-C28 alkanoic acids) and hydrated volcanic glass shards in tephra that are archived in sediments in south-east Alaska and central Yukon. The leaf wax dDMAP estimates, spanning 6.2 to 2.8 Ma, are negative compared to modern which is unexpected for a warmer-than-modern climate as indicated by other proxies. Tephra-dDMAP estimates spanning 6.7 to 0.025 Ma are consistent with North Pacific sea surface temperatures, documenting low dDMAP values during the latest Miocene, peak values during high pCO2 warm intervals (~5 and 3 Ma), and transition to the lowest values on record in the Late Pleistocene. The difference in trends between the two dDMAP reconstructions most likely owes to an inappropriate net-fractionation assumption associated with the leaf wax proxy which remains one of the largest uncertainties in fossil leaf wax derived paleoclimate reconstructions.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".