Global cooling has been strongly associated with the Great Ordovician Biodiversification Event (GOBE), but the underlying mechanisms remain unexplored. To assess whether enhanced biological pump contributed to global cooling during the GOBE, we performed S138Bacarb-S13Ccarb analyses on an Ordovician shallow marine limestone section from South China. Our results show that S138Bacarb in the Ordovician (median 0.73%o) is significantly higher than in other geological periods and reservoirs (median values ranging from-0.18%o to 0.29%o), indicating exceptionally high S138Ba values in the surface ocean in South China, possibly due to plankton radiation, which increased the removal of Ba during the GOBE. Furthermore, shifts in S138Bacarb correlated with long-term increases in S13Ccarb, with positive correlation during the early Tremadocian (Stage 1), followed by negative correlation during the late Tremadocian to Dapingian (Stage 2), and positive correlation from the Darriwilian to Katian (Stage 3). These S138Bacarb-S13Ccarb covariations suggest that marine primary productivity was enhanced during the Ordovician in South China. Additionally, the gradual increase in S13Ccarb is strongly correlated with global cooling and an increase in marine biodiversity, suggesting that plankton radiation during the GOBE may be an important cause of the increased marine primary productivity, thus enhancing organic carbon burial, contributing to the long-term Ordovician cooling, and linking the GOBE and contemporaneous environmental changes.