Evolution of East-West contrast in the subarctic Pacific gyre during the Plio-Pleistocene based on new palynological evidences at ODP Site 882
Bibliographic record
Abstract
Evolution of the temperature contrast in the subarctic gyre is fundamental to better constrain the scheme of the Plio-Pleistocene climate-ocean-ice transition in the northern North Pacific region. The growth of glaciers in Alaska during the early Pliocene is in disagreement with the hypothesis suggesting that development of permanent continental ice in the circum-North Pacific is associated to onset of the modern halocline at 2.7 Ma. Hence, development of warm surface conditions in eastern Pacific during the early Pliocene has been proposed as key mechanism fostering regional evaporation. These assumptions are sustained by model experiments simulating a strong W-E contrast in subarctic Pacific during the Pliocene (Burls et al., 2017) and a reduction of the surface gradient at 2.7 Ma (Haug et al., 2005). However, evolution of the zonal subarctic temperature gradient remains unclear in geological records. In the view to fill this gap, we investigated the dinocyst assemblages at Ocean Drilling Program (ODP) Site 882 located in western subarctic gyre, which were be compared with the Plio-Pleistocene palynostratigraphy previously performed in the Gulf of Alaska. Prior 4.2 Ma, dinocyst assemblages at ODP Site 882 are characterized by cold and cool-tolerant species such as Pyxidinopsis braboi and Filisphaera filifera with occasional occurrence of thermophilic species reflecting cold sea-surface water conditions. This observation is in line with UK37 SST analysed at the study site but contrasts with the highest percentages of thermophilic dinocysts, including Ataxiodinium zevenboomii, Impagidinium velorum and Impagidinium patulum, recorded in the Gulf of Alaska. Hence, our results documented for the first time a strong temperature contrast in the subarctic Pacific gyre with warmer conditions in the East than in the West as previously simulated by the models (Bursl et al., 2017). However, reduction of the zonal temperature contrast was reported at 4.2 Ma, well before the development of the halocline at 2.7 Ma, by the increase of Impagidinium detroitense and Habibacysta tectata over the subarctic gyre. Despite uncertainties regarding the ecology of these two extinct taxa, we tentatively interpreted this change as the development of cool but saline conditions in the subarctic Pacific. Our study acknowledges that a better understanding of the mechanisms driving major climate changes is reinforced by integrating approach combining proxy data and climate models.
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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 | 0.001 |
| 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".