Climate‐Driven Changes in the Ocean's Ventilation Pathways and Time Scales Diagnosed From Transport Matrices
Bibliographic record
Abstract
Abstract We diagnose changes in the decadal‐mean ocean transport over the 21st century as simulated by the ACCESS‐1.3 model under RCP8.5 forcing. A matrix formulation of advection‐diffusion is used to quantify transport into the ocean interior and from the interior back to the surface. We compute the ocean volumes last ventilated at the surface, as well as the volumes next reexposed to the atmosphere, per unit area, and the distributions of water in transit between key ventilation regions. We find that for the 2090s circulation, Antarctic Bottom Water formation and Antarctic ventilation have collapsed but are compensated by increased mode water formation and ventilation at the poleward edge of the southern subtropical gyres. Reexposure of deep water back to the atmosphere in the Antarctic Southern Ocean is also reduced but compensated by enhanced reexposure in the subpolar Southern Ocean. Labrador Sea ventilation is suppressed, while there is increased ventilation in the eastern subpolar Atlantic. The 2090s surface‐to‐surface interbasin transport is much more sluggish than that of the 1990s, with 30–40% reduced volume flow rates. For transport from last ventilation in the subpolar North Atlantic to next ventilation in the tropical Eastern Pacific, the 2090s residence‐time distribution has a ∼40% longer mode with much more slowly decaying tails and correspondingly lagged path densities. The 2090s mean times since last ventilation, as well as the mean times to reexposure are older in the Antarctic Southern Ocean and elsewhere progressively with depth, by up to ∼1,000 years in the abyss.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| 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".