Orbital-Insolation Controlled Porites Coral d13C Seasonality Variations Since the Mid-Holocene in the Northern South China Sea

Coral skeleton delta C-13 is a routinely measured indicator in modern insolation change research, but the knowledge of environmental and climatic signals recorded in its seasonality during geological time is sparse. In this study, we present eight Porites coral delta C-13 records from the mid-late Holocene to the present from the northern South China Sea (NSCS). Compared with the main control factors for modern delta C-13 changes, coral delta C-13 seasonality in the NSCS since the mid-Holocene shows a long-term decreasing trend, which is consistent with the change trend as orbital-induced (precession) insolation seasonal amplitude. By excluding other influencing factors, we speculate that the stronger coral delta C-13 seasonality (18.8%) over the mid-Holocene than modern period is attributable to the metabolic effect, which predicts the stronger coral delta C-13 seasonality under stronger insolation seasonality. Our study has implications for coral delta C-13 seasonality as a potential indicator to record past insolation information under different climatic backgrounds.