Splitting the East China Sea into clear and turbid regimes by nLw555, a CatBoost reconstruction finds the turbid zone is a weak CO2 source and that conventional models overestimate the ECS sink by about 46%
Using a threshold of nLw555 = 1.5 mW cm-2 µm-1 sr-1 from MODIS to separate the East China Sea into Clear Water (CW) and Turbid Water (TW), this study reconstructed surface pCO2 for 2003–2023 with a CatBoost model that treats water type as a categorical input alongside multi-spectral satellite variables, achieving independent-test accuracy of R2 = 0.86 and RMSE = 16.55 µatm and cutting TW RMSE by up to about 81% relative to conventional models; the 21-year climatology gives CW 361.2 µatm and TW 415.1 µatm, with TW acting as a weak net source (+0.50 Tg C yr-1) driven by positive non-thermal anomalies (+28.09 µatm), implying conventional models overestimate total ECS carbon uptake by roughly 46% (about 4.04 Tg C yr-1).