Two annually resolved ice core records, one drilled on Mutztagata (7,000m above sea level) on the western slope (dated 1952-2002) and the other drilled on Kuokuosele (5,600m above sea level) on the southwestern slope (dated 1900-2010) of the Pamir Plateau of the northwestern Tibetan Plateau (TP), were selected to study possible El Nino-Southern Oscillation (ENSO) influences on the northwestern TP. O-18 at KKSL was more enriched, though both records varied in phase. Eight of the 10 noticeably strong El Nino events since 1955 corresponded to O-18 depletions in both ice core records, which were followed by O-18 enrichment. Atmospheric circulation indices, including water vapor flux and divergence, had a coincidence of a positive Indian Ocean Dipole mode with El Nino events, which contributed to the northward transport of southerly flows from the western Indian Ocean; its convergence with midlatitude wind flows at high levels depleted O-18 levels. The meridional shift in the Asian-Pacific subtropical high induced by latent heat release due to precipitation in the northwestern Pacific was found to play an important role in initiating convergence. A statistical analysis confirmed the significant correlations in O-18 with the ENSO index and tropical and subtropical summer monsoon circulations. We noted that the dominant circulation pattern over the northwestern TP was characterized by a midlatitude flow regime that had a teleconnection with tropical sea surface temperatures. Therefore, ENSO is one of a variety of influences on ice core O-18 on the TP.