Estimation of 137Cs inventories in each ocean basin by a global ocean general circulation model for the global database interpolation
Bibliographic record
Abstract
<p>Radioactive cesium (<sup>137</sup>Cs) is distributed in the global ocean due to global fallout by atmospheric nuclear weapons tests, releases from reprocessing plants in Europe, and supplied to the ocean by the Fukushima Daiichi Nuclear Power Plant (1F NPP) accident. In order to detect future contamination by radionuclides, it is necessary to understand the global distribution of radionuclides such as <sup>137</sup>Cs. For this purpose, observed data have been summarized in a historical database (MARIS) by IAEA. The spatio-temporal density of the observations varies widely, therefore simulation by an ocean general circulation model (OGCM) can be helpful in the interpretation of these observations.</p><p>In order to clarify the behavior of <sup>137</sup>Cs in the global ocean, OGSM simulations were conducted. Parallel Ocean Program version 2 (POP2) of the Community Earth System Model version 2 (CESM2) is employed. The horizontal resolution is 1.125 degree of longitude, and from 0.28 degree to 0.54 degree of latitude. There are 60 vertical levels with a minimum spacing of 10 m near the ocean surface, and increased spacing with depth to a maximum of 250 m. The simulated period was from 1945 to 2030 with the circulation forced by repeating (“Normal Year”) atmospheric conditions. As input sources of <sup>137</sup>Cs to the model, global fallout from atmospheric nuclear tests, releases from reprocessing plants in Europe, and input from the 1F NPP accident were considered. It was assumed that the input conditions in 2020 would continue after 2020.</p><p>The simulated <sup>137</sup>Cs activity agrees well with the observed data in the database, especially in the Atlantic and Pacific Oceans where the observation density is large. Since <sup>137</sup>Cs undergoes radioactive decay with a half-life of 30 years, the inventory for each basin is the difference between the decay corrected cumulative input and flux. In the North Pacific, the inventory reached its maximum in 1966 due to the global fallout by atmospheric nuclear weapons tests. Fluxes from the North Pacific to the Indian Ocean, Arctic Ocean, and Central Pacific were positive, and the North Pacific was a source of supply for other ocean basins. The 1F NPP accident caused a 20% increase in the inventory in 2011. In the North Atlantic, the inventory reaches its maximum in the late 1970s, due to the releases from the reprocessing plant. The outflow flux from the North Atlantic to the Greenland Sea is larger than the other fluxes and is a source of supply to other ocean basins. After 2000, the inflow flux to the North Pacific from the Labrador Sea and the South Atlantic is larger than the outflow flux.</p><p>The time series of <sup>137</sup>Cs inventory in each ocean basin and the fluxes among ocean basins were quantitatively analyzed by OGCM simulations, and the predictions for the next 10 years were made.  The <sup>137</sup>Cs activity concentrations by global fallout can be detected in the global ocean after 2030. The OGCM simulations will be useful in planning future observations to fill the gaps in the database.</p>
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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 | 0.000 | 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 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".