Distributions of Protactinium‐231 and Thorium‐230 confirm the critical influence of meridional overturning circulation in the Indian Ocean
Bibliographic record
Abstract
Abstract Sedimentary 231Pa/230Th has been used as a proxy for understanding changes in ocean circulation and productivity over the last glacial–interglacial cycle. Its application relies on the influence of meridional overturning circulation (MOC) and particle scavenging on the distribution of 231Pa and 230Th in the water column and sediments. While previous studies have addressed the role of MOC on the 230Th and 231Pa water profiles and sedimentary 231Pa/230Th in the Atlantic and Pacific Oceans, including the influence of boundary scavenging in the latter, the impact of these processes in the Indian Ocean remains unresolved. This study employs a two‐dimensional scavenging model with prescribed overturning schemes to simulate the latitudinal distribution of 230Th and 231Pa in the water column and sediments of the Indian Ocean. The water column profiles of both nuclides deviate from linearity, reflecting the influence of deep convection, advection, and upwelling controlled by MOC. Additionally, bottom scavenging within the nepheloid layer and boundary scavenging significantly depletes 231Pa in the Madagascar Basin. The gradual decrease in sediment 231Pa/230Th below 1500 m in the main basins is primarily linked to MOC, while boundary scavenging contributes to systematically lowering the 231Pa/230Th. These findings point to the potential of sedimentary 231Pa/230Th as a proxy for studying the alteration of deep ocean circulation and particle flux in the Indian Ocean.
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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) | 0.001 | 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".