Middle Miocene evolution of East Asian summer monsoon precipitation in the northeast part of the Tibetan Plateau based on a quantitative analysis of palynological records.

Characterized by elevated pCO 2 levels and global warmth, the mid-Miocene climate is a valuable analogue for investigating how the East Asian Summer Monsoon (EASM) may evolve at different time scales. In this paper, we present a quantitative EASM precipitation record with a temporal resolution of ∼14 kyr during the mid-Miocene (∼15.97 to 13.64 Ma) by applying the probabilistic CREST (Climate Reconstruction Software) method to palynological records from the northeast part of the Tibetan Plateau. Reconstructed mid-Miocene EASM precipitation (∼860 mm) was almost twice that of today (∼450 mm), indicating much stronger EASM intensity. The reconstruction shows a gradual long-term decline on which was superimposed a stronger EASM period (∼15.97–14.54 Ma) followed by a relatively stable period (∼14.54–13.84 Ma) and a short period of reduced precipitation (∼13.84–13.64 Ma). The correspondence of EASM precipitation changes with the mid-Miocene climate optimum and west-east thermal gradients in equatorial Pacific suggests these two factors were the main driving forces for EASM evolution from ∼15.97 to 14.54 Ma, whereas the combined impact of global cooling and the northward shift of the Intertropical Convergence Zone is probably responsible for the slight decline of the EASM from ∼14.54 to 13.84 Ma. The weaker EASM between ∼13.84 and 13.64 Ma was most likely a response to the global significant cooling event Mi-3. On orbital time scales, the precipitation records exhibit a dominant ∼400 kyr periodicity, indicating EASM changes were mainly paced by eccentricity via the modulation of precessional amplitude, and the East Antarctic Ice Sheet variations were probably another important driving force. • A high-resolution, quantitative mid-Miocene EASM precipitation record was obtained. • The mean mid-Miocene MAP of ∼860 mm was almost 2 times that of today in NE TP. • Global temperature played key role in long-term mid-Miocene EASM evolution. • West-east thermal gradients in EP, ITCZ are also vital drivers in some intervals. • Orbitally, mid-Miocene EASM variability was dominated by eccentricity forcing. [ABSTRACT FROM AUTHOR]