Fig. 5: Conceptual model for hydroclimatic drivers in the western Pacific during the Bølling–Allerød (B–A) interstadial.
From: Persistent El Niño-like conditions over the western Pacific during the Bølling–Allerød interstadial
During the last deglaciation, boreal fall September–October–November (SON) insolation minima caused uniform cooling of the tropical Pacific atmosphere, generating westerly anomalies over the western equatorial Pacific (WEP). By the onset of the B–A, Northern Hemisphere (NH) ice-sheet retreat passed a critical threshold, inducing eastern equatorial Pacific (EEP) cooling and central equatorial Pacific (CEP) warming, which triggered central Pacific (CP) El Niño-like conditions. This shifted the ascending branch of the Pacific Walker Circulation toward the CEP, causing humid conditions there and further strengthening westerly anomalies—establishing a positive feedback that enhanced CP El Niño. Combined with Southern Hemisphere (SH) forcing, this led to persistent dryness and/or seasonal aridity in the western Pacific, ultimately promoting the retreat of C3 vegetation and expansion of open-canopy lowland C3 ecosystems in Borneo. Note: core CG18 was collected from the Northwest Borneo trough in the southern South China Sea (SCS).
