Coupled orbital and sea-level forcing on the Pacific Walker Circulation during the past 800 kyrs

Abstract Over recent decades an anomalous El Niño–Southern Oscillation (ENSO) configuration became more frequent, characterized by central Pacific temperature anomalies and a split-Pacific Walker Circulation. This so-called ENSO-Modoki pattern strongly alters precipitation distribution across the tropics, however, its potential forcings and long-term variability remain yet elusive. To track split-Pacific Walker Circulation states through the geological past, we reconstructed an ENSO Modoki Index for the past 800,000 years based on sea-surface temperature gradients across the equatorial Pacific. We show that glacial periods favored El Niño Modoki-like conditions, while periodic Sunda Shelf submersion after ~250 ka shifted the mean state towards La Niña Modoki-like conditions in interglacial periods. These findings provide the first evidence that ENSO Modoki has been a persistent feature of Pacific climate and highlights the long-term sensitivity of Pacific Walker Circulation dynamics to orbital and sea-level forcing.