Sudden freshening and cooling of western North Atlantic slope water at the onset of the Little Ice Age based on Magnesium-to-Calcium ratio and oxygen stable isotope record.
Bibliographic record
Abstract
The Little Ice Age (LIA), a period from ~1400 CE to 1850 CE, was characterized by colder winters and more frequent extreme weather events, particularly in the Northern Hemisphere. While the exact causes of the LIA remain a topic of ongoing research, evidence suggests that changes in ocean circulation likely contributed to the observed global cooling, although the specific mechanisms and drivers of these changes are not yet fully understood. Here, we aim to generate new knowledge to help us better understand how ocean circulation changed before, during, and after this climatic event. More specifically, using marine cores collected at the head of the Laurentian Channel in the Lower Estuary of the St. Lawrence, we investigated variations in the temperature and seawater oxygen isotopic signal of western North Atlantic slope waters to assess the relative strength of the Labrador Current and the Gulf Stream. First, we established a Mg/Ca-temperature calibration curve for Globobulimina auriculata from the bottom water of the Lower St. Lawrence Estuary based on instrumental temperature data and geochemical analysis from a short, century-old sediment box core. Then, using a longer piston core, we produced new downcore measurements of Mg/Ca in Globobulimina auriculata for the LIA. We then coupled this new temperature reconstruction with existing oxygen isotope data (d18Ocalcite) to disentangle the influence of temperature on the d18Ocalcite. The resulting d18Oseawater record is interpreted in terms of changes in in their isotopic composition due to changes in freshwater input, and relative strength and position of the Labrador Current and the Gulf Stream. Our interpretation suggests dominance of fresh Labrador Sea-derived waters around 1500 CE, and during most of the LIA. In the later stage of the LIA, after 1800 CE, our data indicate a steep increase in the influence of Atlantic-derived waters, consistent with a northward shift of the Gulf Stream. The record of the ~1800-1950 CE interval exhibits high-amplitude variability, with a sudden freshening event at the end of the LIA. The upper part of the record, after 1950 CE, is characterized by a regional warming trend that has been widely documented in previous studies conducted in this area.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".