Mid to late Holocene ENSO variability reconstructed by high-resolution Tridacna Sr/Ca records from the northern part of the South China Sea

The El Niño-Southern Oscillation (ENSO) dominates global interannual climate variability and has important socio-economic and environmental consequences. However, determining the history of ENSO variability and its long-term response to climate forcing remains an ongoing challenge owing to the limit of instrumental records. In this study, ENSO variability was reconstructed using monthly-resolution records of Sr/Ca ratios obtained from subfossil giant clam shells (Tridacna squamosa) during three windows from the 5000 to 3000 yr B.P. in the northern part of the South China Sea (SCS). ENSO variability during the mid to late Holocene was also investigated through comparison with other published monthly Tridacna Sr/Ca records from the northern SCS, and findings show a gradually intensified ENSO variability from the mid to late Holocene. This intensification of ENSO variability over the study period is predicted by model simulations, and is considered to be a consequence of precessional forcing. Our study highlights that the monthly Sr/Ca ratios from Tridacna shells of the northern SCS can be used as a high-resolution indicator of past interannual climate variability and can provide a new perspective for paleo-ENSO reconstructions.