Tephra-based time-markers from the Last Glacial Period recorded in the North Atlantic: an emerging tool for an east-west synchronization of paleoclimate records
Bibliographic record
Abstract
Geochemically distinct volcanic ash (tephra) deposits have the potential to act as a key geochronological tool to independently synchronize independent paleoclimate archives. Recent advances in the detection of invisible (crypto) tephra have led to the ongoing development of regional tephra frameworks. These frameworks provide an overview of the spatial coverage of existing geochemically distinct tephra horizons attributed to dated eruptions. Hence, these developing frameworks produce an essential tool for precise correlation of different and/or disparate climate archives within a certain region. Here, using cryptotephra analysis, we investigate the potential occurrence of two well-known tephra horizons from the Last Glacial Period (i.e. FMAZ II-1 (26.7 ka b2k) and NAAZ II (II-RHY-1) (55.3 ka b2k)), in five different marine sediment cores from the Denmark Strait, as well as the Nordic, Irminger and Labrador Seas. We have successfully identified FMAZ II-1 in both the Nordic and Irminger Seas. Even more so, this study presents the first identification of an isochronous FMAZ II-1 horizon detected in the Irminger Sea. This clearly demonstrates an increased potential for tephrochronology within this region. In addition, NAAZ II (II-RHY-1) was also recorded in the Denmark Strait, the Irminger Sea and the Labrador Sea. Using those identified tephra time-markers allows us to discuss the synchronization of paleoclimate records retrieved from the in this study and previously investigated marine sediment cores. We focus on both time periods when the tephra time-markers were deposited (i.e. Greenland Stadial-3 (FMAZ II-1) and Greenland Interstadial-15 (NAAZ II (II-RHY-1)) with the aim to provide synchronized records of ocean temperature and salinity changes. Therefore, we use Mg/Ca ratios of benthic foraminifera and stable isotopes (d18O & d13C) of benthic and planktonic foraminifera. By coupling the paleoclimatic information with the identified tephra time-markers, we provide a robust overview of the climatic conditions in the North Atlantic Ocean during these two time periods.
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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 | 0.000 | 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".