The modern pattern of the Asian monsoon is thought to have formed around the Oligocene/Miocene transition and is generally attributed to Himalaya–Tibetan Plateau (H–TP) uplift. However, the timing of the ancient Asian monsoon over the TP and its response to astronomical forcing and TP uplift remains poorly known because of the paucity of well-dated high-resolution geological records from the TP interior. Here, we present a precession-scale cyclostratigraphic sedimentary section of 27.32 to 23.24 million years ago (Ma) during the late Oligocene epoch from the Nima Basin to show that the South Asian monsoon (SAM) had already advanced to the central TP (32°N) at least by 27.3 Ma, which is indicated by cyclic arid–humid fluctuations based on environmental magnetism proxies. A shift of lithology and astronomically orbital periods and amplified amplitude of proxy measurements as well as a hydroclimate transition around 25.8 Ma suggest that the SAM intensified at ~25.8 Ma and that the TP reached a paleoelevation threshold for enhancing the coupling between the uplifted plateau and the SAM. Orbital short eccentricity-paced precipitation variability is argued to be mainly driven by orbital eccentricity-modulated low-latitude summer insolation rather than glacial-interglacial Antarctic ice sheet fluctuations. The monsoon data from the TP interior provide key evidence to link the greatly enhanced tropical SAM at 25.8 Ma with TP uplift rather than global climate change and suggest that SAM’s northward expansion to the boreal subtropics was dominated by a combination of tectonic and astronomical forcing at multiple timescales in the late Oligocene epoch.

As the dominant ocean-atmosphere coupled mode of interannual variability in the climate system, the El Niño-Southern Oscillation (ENSO) exhibits notable impacts through atmospheric teleconnections on the climate record in alpine glaciers. Pollen collected from snow samples on the Quelccaya Ice Cap had high concentrations during the La Niña years and low concentrations during the El Niño years (Reese & Liu, 2005). Annually resolved pollen records from the Sajama Ice Cap indicated high pollen concentrations during El Niño years, which was attributed to increased sublimation (Liu et al., 2007). The pollen and chemical records extracted from ice cores recovered from Nevado Coropuna Mountain revealed two high concentration peaks associated with El Niño events in 1982 -1983 and 1992(Herreros et al., 2009.The Tibetan Plateau (TP) is the largest alpine glacier preservation area in the world. The interannual climate changes recorded in ice cores from the northern TP to the southern TP are modulated by ENSO conditions. Yang et al. (2000) found that negative precipitation anomalies were associated with El Niño years in cores from the Guliya Ice Cap. Yang et al. (2018) suggested that eight of 10 noticeably strong El Niño events corresponded to δ 18 O depletion events in Kuokuosele and Mutztagata ice cores extracted from the Pamir Plateau. Wang et al. (2003) showed that the air temperature during the warm season, as recorded by δ 18 O, retrieved from an ice