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The processes controlling middle-latitude environmental changes are poorly understood. Both high-latitude ice sheets and tropical oceans can affect climate and environments in middle latitudes, but separating their relative contribution is challenging. Coincidence of intensive Northern Hemisphere glaciations and increased dust accumulation rates at similar to 2.7 Ma on the Chinese Loess Plateau and North Pacific Ocean is often used to indicate high latitudes' dominant role on middle-latitude climate change. Here we present new and compile available evidence from the Qaidam Basin and the Tarim Basin of central Asia demonstrating a phase of drying at similar to 3.3 Ma. The drying is synchronous with proposed timing of closure of the Indonesian Seaway, which has been suggested to cause significant oceanic surface heat adjustments and corresponding decreased heat and moisture transport to middle/high latitudes. These new results suggest a tropical forcing of aridification for the late Pliocene central Asian environmental evolution.

Plain Language Summary The timing and forcing mechanisms for past climate changes are instructive to predict future variations. It is widely believed that the aridification of central Asia and changes in monsoonal climate on the Chinese Loess Plateau formed at the Pliocene-Quaternary boundary forced by intensive Northern Hemisphere glaciations at similar to 2.7 Ma. In this study we demonstrate that aridification began earlier within the Qaidam and Tarim Basins, at similar to 3.3 Ma, when no significant change occurred for Northern Hemisphere ice sheets. Instead, this event was aligned with tropical Indian Ocean cooling as a result of closure of the Indonesian Seaway. Thus, we attribute this earlier drying event to tropical forcing rather than cryospheric change. This study reinterprets the forcing of aridification in central Asia and suggests that understanding future environments in this ecologically fragile region needs to consider tropical forcing.