A prediction model for 137Cs in surface seawater of China’s coastal waters based on AI oceanography method

A hybrid framework named “TRR–LSTM–TRR” is developed to reconstruct and predict 137 Cs activity concentrations in surface seawater of China’s coastal seas. The model integrates a bound-constrained Trust-Region Reflective (TRR) exponential baseline, an LSTM-based residual-learning network, and a physically constrained exponential refit. Historical observations from the Bohai Sea, Yellow Sea, East China Sea, and South China Sea during 1960–2017 were compiled (833 station records after data-quality corrections). The reconstructed environmentally effective half-lives were 10.52, 14.84, 15.05, and 16.40 a for the four seas, respectively, indicating the fastest attenuation in the Bohai Sea and the slowest in the South China Sea. The residual correction reduced absolute prediction errors in all basins; under the temporal holdout (training on 1960–2010, testing on 2011–2017) mean absolute errors were 0.30–0.61 Bq m −3 . Because the recent records are few and low-valued, long-term projections are reported with 90% ensemble prediction intervals rather than as point estimates. Taking 0.2 Bq m −3 as the detection limit, the Bohai, East China, Yellow, and South China Seas are expected to fall below this threshold around 2036, 2049, 2053, and 2055, respectively.