Fig. 1: Map of the tropical Pacific Ocean showing the study site, sea surface temperature, and sea surface temperature variability.

a Average ERSST v5 sea surface temperature (SST) 1854–2019⁵². b Total SST variability as shown by the SST standard deviation. c Interannual variability, shown as the standard deviation of SST anomalies. Interannual variability is dominated by ENSO, thus variability at this site is largely determined by ENSO. The location of Line Islands cores 17PC and 14MC in the central tropical Pacific (this study) is shown as a white star with black outline; ODP Site 851 in the Eastern Tropical Pacific is shown as a black star with white outline. The solid black arrow in a schematically shows the mean location of the Equatorial Under Current. The dotted arrow depicts the location of the Equatorial Counter Current, whose depths are inversely related (based on ref. ³⁶).