Eastern equatorial Pacific cold tongue evolution since the late Miocene linked to extratropical climate.

The timing and mechanisms of the eastern equatorial Pacific (EEP) cold tongue development, a salient feature of the tropical ocean, are intensely debated on geological time scales. Here, we reconstruct cold tongue evolution over the past 8 million years by computing changes in temperature gradient between the cold tongue and eastern Pacific warm pool. Results indicate that the cold tongue remained very weak between 8 and 4.3 million years ago, implying much weaker zonal temperature gradients prevailing during the late Miocene-Pliocene, but then underwent gradual intensification with apparently increasing sensitivity of the cold tongue to extratropical temperature changes. Our results reveal that the EEP cold tongue intensification was mainly controlled by extratropical climate.