Ranges (amplitudes) of isotopic ratios in speleothems, with particular reference to samples from the centre of North America
Bibliographic record
Abstract
This paper compares unstable and stable isotope ratios measured in a speleothem core from the Nevada desert (the well-known DH 11) with speleothems at the centre of the continent in the Black Hills of South Dakota. All samples grew over most of the past 500,000 y. The thermal calcite in the large Nevadan desert basin displays a range of the initial U ratio ( 234 U/ 238 U0) of only 0.25 and is much enriched in 234 U, reflecting selective leaching in a very low energy weathering environment. Similar thermal calcite from a much smaller basin the Black Hills (Wind Cave) is less homogenised (U/U0 range is ~0.5) and less enriched as a consequence of its more vigorous sem-arid weathering environment. Both display glacial-interglacial cyclicity in the ratio. A vadose speleothem from Jewel Cave, Black Hills, has a U/U 0 range of 0.75 and many erratic features attributable to rapidly changing local conditions in the overlying tall grass- coniferous forest vegetal transition. O and C stable isotopes are again homogenised in the large Nevada basin: the range is 2.8 ‰ 18 O and 1.2 ‰ 13 C, encompassing all glacial-interglacial cyclicity. In the Wind Cave thermal calcites the range again is roughly double, an effect of lesser homogenisation taking place in the smaller aquifer. There is also a perturbation of the signals of ~100 ky duration that may have been caused by release of deep CO 2 . 18 O and 13 C measurements in the Jewel Cave vadose sample form a broad envelope that encloses the Black Hills thermal calcite data, indicating that the full range, glacial – interglacial, of speleothem 18 O was probably 10 ‰ here in the centre of the continent, which may be compared to 1.2 ‰ estimated at the sources of the precipitation in the Gulf and Caribbean. 13 C of the vadose speleothem ranged 7.0 ‰ in the Black Hills, oscillating between moderate and very low (desert-like) levels of soil CO 2 activity.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 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".