Absolute paleotemperatures during the Laschamps geomagnetic excursion
Bibliographic record
Abstract
The link between geomagnetic excursions and climate is an exciting but still unresolved topic. The idea reposes on the increased solar and cosmic ray radiation in response to the weakened magnetic field during the transitional fields accompanying a geomagnetic reversal or excursion. However, a direct climate response to the variations of the Earth magnetic field is not yet demonstrated in the geological record. A major limitation resides in the fact that paleomagnetic data are usually extracted from igneous or sedimentary rocks, which usually provide no or poor-quality paleoclimate information. Recent advances in speleothem magnetism fill this gap and open a new door to investigate the link between climate and the variation of the Earth magnetic field in the same geological archive. Here we document absolute paleotemperatures based on water isotopes in fluid inclusions from a Portuguese stalagmite that recorded the Laschamps geomagnetic excursion (~42 kyrs). The stalagmite was dated by radiocarbon method. Paleomagnetic data show the complete record of the Laschamps geomagnetic excursion, with paleomagnetic poles moving from the north pole down to the south pole and returning to the original position in ~3000 kyrs. Paleointensity data show a weakened magnetic field associated with the migration of the paleomagnetic pole. Absolute paleotemperatures were calculated using the fluid inclusion hydrogen isotope (d2H) and the calcite-water isotope fractionation paleothermometer on 19 samples encompassing the Laschamps event. The data show increased absolute temperatures just before and during the Laschamps. However, a strong correlation is noted between the absolute temperature calculated here and the oxygen isotope composition of the NGRIP ice core. Although the relation between paleotemperatures and the Laschamps event is not yet fully demonstrated in this case, the combination of paleomagnetic techniques coupled to isotope composition in speleothems offers new and promising perspectives to investigate the relationship between climate and the Earth magnetic field. This project is funded by Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025, UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020), and PTDC/CTA-GEO/0125/2021.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 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 | 0.001 |
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".