Coral-based reconstruction of interannual and decadal SST variability in the northern South China Sea during the mid-Holocene

High-resolution proxy records are essential for understanding climate variability on interannual to decadal timescales. In this study, fossil Porites corals from Tanmen, Hainan Island in the northwestern South China Sea, were used to reconstruct mid-Holocene sea surface temperature (SST) variability. Monthly-resolution SST was reconstructed from coral Sr/Ca ratios, yielding a 67-year record centered around ~ 5200 year BP. In addition, coral growth rates were used to generate an annual-mean SST record spanning ~ 180 years (~ 5257–5076 year BP). Spectral analysis of the SST records reveals significant periodicities within the 2–7-year band, consistent with ENSO variability, and an additional periodicity around ~ 20 years, which may be associated with Pacific Decadal Oscillation (PDO)–like variability. Comparison of SST parameters indicates that winter SST dominates SST seasonality and exhibits the strongest relationship with PDO signals. Phase analysis suggests that El Niño events occurred more frequently during positive PDO-like phases, whereas La Niña events were more common during negative PDO-like phases. These results indicate that ENSO and PDO influences, as well as their interaction, were likely already active in the northern South China Sea during the mid-Holocene.