Ecosystem Expansion Drove the Great Ordovician Biodiversification Event and Coeval Environmental Changes

The Great Ordovician Biodiversification Event (GOBE) represents the largest radiation of marine life during the Phanerozoic. However, its causes and consequences remain debated, particularly regarding whether environmental changes drove biodiversity increases or vice versa. In this study, we present high-resolution biodiversity records alongside δ138Bacarb, δ13Ccarb, and δ15Nbulk data from South China. Our results indicate that the onset of the GOBE was accompanied by concurrent changes in the diversity of plankton, nekton, and benthos, suggesting coordinated development of ecological modes during the rapid expansion of marine ecosystems. The initiation of the GOBE in the Early Ordovician predated a major shift in δ15N values from the late Tremadocian to the middle Darriwilian, implying that changes in marine ecosystems drove the evolution of nutrient cycles in South China, rather than the reverse. Moreover, shifts in δ138Bacarb correlate with long-term δ13Ccarb trends: a positive correlation during the early Tremadocian, followed by a negative correlation from the late Tremadocian to the Dapingian, and a renewed positive correlation from the Darriwilian to the Katian. This pattern suggests episodically enhanced marine primary productivity during the Ordovician in South China. The gradual increase in δ13Ccarb is strongly correlated with global cooling and rising marine biodiversity, implying that plankton radiation during the GOBE may have been an important driver of increased primary productivity. This would have enhanced organic carbon burial and contributed to long-term global cooling, thereby linking the GOBE with contemporaneous environmental changes. Together, these findings provide critical insights into the connections between marine ecosystem evolution, nutrient cycling, and environmental conditions during the Ordovician Period.