A millennium of cold-water coral habitat loss in the East Pacific during low ENSO variability in the mid- to late Holocene.

The evolution of El Niño-Southern Oscillation (ENSO) under past and future climate change and its influence on marine ecosystems is highly debated. To examine links between tropical climate variability, high-latitude feedbacks, and deep-sea ecosystems, we have analyzed over 900 subfossil cold-water scleractinian corals from the Galápagos Archipelago. U-Th dating shows that these corals have inhabited the region for at least 117,000 y, thriving at depths down to ~1,000 m. However, we find a millennial-scale gap in coral occurrence ~5,000 y ago, coinciding with reduced ENSO variability and a persistent La Niña-like state. Coral presence resumed as ENSO cyclicity strengthened again toward modern conditions. While shallow-water coral growth has been shown to generally decline in the equatorial Pacific during El Niño surface warming, the mid- to late Holocene loss of cold-water corals may reflect the opposite: prolonged La Niña-like conditions. We hypothesize that stronger upwelling at this time intensified the oxygen minimum zone, adversely affecting cold-water coral habitats. With ENSO projected to change under continued ocean warming, the potential vulnerability of cold-water corals to future climate change is a growing concern. This study underscores the value of understanding past ENSO behavior and its impact on deep-sea ecosystems in a warming world.