The Role of Oceanic Heat Transport and Wind Stress Forcing in Abrupt Millennial-Scale Climate Transitions
Bibliographic record
Abstract
Abstract The last glacial period was punctuated by rapid climate shifts, known as Dansgaard–Oeschger events, with strong imprint in the North Atlantic sector suggesting that they were linked with the Atlantic meridional overturning circulation. Here an idealized single-hemisphere three-dimensional ocean–atmosphere–sea ice coupled model is used to explore the possible origin of the instability driving these abrupt events and to provide a plausible explanation for the relative stability of the Holocene. Focusing on the physics of noise-free millennial oscillations under steady external (solar) forcing, it was shown that cold climates become unstable, that is, exhibit abrupt millennial-scale transitions, for significantly lower freshwater fluxes than warm climates, in agreement with previous studies making use of zonally averaged coupled models. This fundamental difference is a direct consequence of the weaker stratification of the glacial ocean, mainly caused by upper-ocean cooling. Using a two-hemisphere configuration of a coupled climate model of intermediate complexity, it is shown that this result is robust to the added presence of a bottom water mass of southern origin. The analysis reveals that under particular conditions, a pronounced interdecadal variability develops during warm interstadials. While the nature of the instability driving the millennial oscillations is identical to that found in ocean models under mixed boundary conditions, these interstadial–interdecadal oscillations share the same characteristics as those previously found in ocean models forced by fixed surface fluxes. The wind stress forcing is shown to profoundly affect both the properties and bifurcation structure of thermohaline millennial oscillations across a wide range of variation of freshwater forcing. In particular, it is shown that the wind stress forcing favors the maintenance of thermally direct meridional overturning circulations during the cold stadial phases of Dansgaard–Oeschger cycles.
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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 | 0.001 | 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 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".