Extended Data Figure 7 : Evolution of the BJ index and its components.

From: Evolution and forcing mechanisms of El Niño over the past 21,000 years

Extended Data Figure 7

Evolution of ocean–atmosphere feedbacks in the eastern equatorial Pacific region (180° E–80° W, 5° S–5° N) for interannual (1.5–7-year band) ENSO variability in 100-year windows in TRACE. a, ENSO amplitude (red) and the BJ index (purple). b, The two negative (damping) feedbacks (surface heat flux feedback (cyan) and mean advection feedback (green, offset by +2)) and the three positive feedbacks (zonal advection feedback (blue), Ekman upwelling feedback (red) and thermocline feedback (brown)), as well as the (sum) total feedback (BJ index, purple, offset by +2). The ENSO amplitude largely follows the BJ index (an increasing trend) in the Holocene, but not in the deglaciation, suggesting the dominant role of ocean–atmosphere feedback for ENSO intensification in the Holocene, but not for millennial variability in deglaciation.