Tab. 1

Data sources for coral geochemical indicators"

Fig. 1

Spatial correlation between SST in the southern SCS (lagged by 4 months) and Niño3.4 index. Created by Climate Explorer, an online tool (Trouet et al, 2013). The SST in the southern SCS shows a significant positive correlation (P<0.1) with the Niño3.4 index. The SST data used for this analysis were derived from the monthly HadISST dataset, covering the period from 1950 to 2020 (https://www.metoffice.gov.uk/hadobs/hadisst/). Black dots on the map indicate coral sampling locations: (1) Hòn Tre Island; (2) Yongshu Island; (3) Anemone’s Garden, (4) Palawan Island"

Fig. 2

Correlation analyses (a-j) and time series (k-p) of monthly-resolution geochemical proxies in coral skeletons (black folded line) with sea surface temperature (SST) from southern SCS and local SST records (gray dotted line), both processed with a 13-month moving average. Asterisks (*) represent statistically significant correlations (P<0.05)"

Fig. 3

Signal processing of instrumental SST sequence: (a) time-domain plot of the Niño3.4 signal before and after processing, with the dotted line representing the raw signal sequence and the solid line representing the signal sequence after applying a 12~48 Hz filter; (b) frequency-domain plot of the original Niño3.4 signal, showing that the frequency distribution is primarily concentrated in the 12~48 Hz ( 1~4 years) frequency band; (c) frequency-domain plot of the Niño3.4 signal after 12~48 Hz filtering; (d) time series of Niño3.4 (solid line) and sea surface temperature anomaly (SSTA) (dotted line) in the southern SCS after 12~48 Hz band-pass filtering; (e) results of the lagged correlation analysis, showing that the correlation with Niño3.4 reaches its peak when the SST in the southern SCS is lagged by 4 months, with a correlation coefficient of 0.72 (P<0.05)"

Fig. 4

Classification of El Niño and La Niña events into moderate, intense, and extreme categories, using ±1σ and ±2σ standard deviations as thresholds. (a) Time series of Niño3.4; (b) time series of SSTA in the southern SCS after 12~48 Hz band-pass filtering"

Fig. 5

Different types and intensities of ENSO events as recorded by coral geochemical proxies: (a) different types and intensities of ENSO events recorded in the Niño3.4 index series from 1950 to 2020 as reference standard; (b) Sr/Ca anomalies from Hòn Tre Island, 1950-2010; (c) Sr/Ca anomalies from Anemone’s Garden, 1982-2016; (d) δ18O anomalies from Yongshu Island, 1951-1999; (e) δ18O anomalies from Palawan Island, 1950-1981; (f) δ18O anomalies from Anemone’s Garden, 1982-2016; Neutral warming events (▽) were excluded from subsequent statistical analyses"

Fig. 6

Responses of coral skeletal geochemical proxies and SST in the southern SCS to different grades and types of ENSO events"