Paleoclimate support for a persistent dry island effect in the Colombian Andes during the last 4700 years
Bibliographic record
Abstract
We investigated middle- and late-Holocene hydroclimate patterns in the Colombian Andes using indicators of watershed erosion (lithic abundance), precipitation intensity (% silt), lake-level variability (organic carbon and nitrogen, % sand, and diatoms), and fire frequency (fossil charcoal) from a ~4700-year-long sediment archive from Laguna de Ubaque, a small sub-alpine lake on the eastern flank of the eastern Colombian Andes. Our results indicate reduced precipitation, low lake levels, and increased fire occurrence at Ubaque between 4700 and 3500 cal. yr BP (hereafter BP). Precipitation and lake levels increased abruptly while fire occurrence decreased between 3500 and 2100 BP, with the exception of a 300-year dry phase between 2800 and 2500 BP. Although wetter than the 4700–3500 BP interval, precipitation decreased, lake levels fell, and fire occurrence increased after 2100 BP, but with high-frequency variability. Comparison of the Ubaque results with other Colombian paleoclimate records (e.g. Lakes Fúquene and La Cocha) supports an antiphase pattern of precipitation between the high/interior Andes and frontal slope sites. This spatial pattern of variability is consistent with modern responses to the changes in terrestrial atmospheric convection associated with the so-called ‘dry island’ effect. Further comparison with paleoclimate records from Venezuela suggests that the millennial trend toward increasing frontal slope precipitation is consistent with orbitally induced increases in Andean atmospheric convection. Sub-orbital dry island–like hydroclimate variability suggests that other mechanisms that affect Northern Hemisphere convection may act to enhance or diminish this effect on centennial and shorter timescales.
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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 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 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".