East Asian summer monsoon precipitation variations in China over the last 9500 years: A comparison of pollen-based reconstructions and model simulations

• Published in: The Holocene
• Main Authors: Li, Jianyong, Ilvonen, Liisa, Xu, Qinghai, Ni, Jian, Jin, Liya, Holmström, Lasse, Zheng, Zhuo, Lu, Houyuan, Luo, Yunli, Li, Yuecong, Li, Chunhai, Zhang, Xiaojian, Seppä, Heikki
• Format: Article in Journal/Newspaper
• Language: English
• Published: SAGE Publications 2015
• Subjects: Sea ice
• Online Access: http://dx.doi.org/10.1177/0959683615612564; http://journals.sagepub.com/doi/pdf/10.1177/0959683615612564; http://journals.sagepub.com/doi/full-xml/10.1177/0959683615612564

To better understand the long-term changes of the East Asian summer monsoon precipitation ( P jja ), quantitative reconstructions and model simulations are needed. Here, we develop continental-scale pollen-based transfer functions for P jja with weighted averaging–partial least squares (WA-PLS) regression and a Bayesian multinomial regression method. We apply these transfer functions to a set of fossil pollen data from monsoonal China for quantitatively reconstructing the P jja changes over the last 9500 years. We compare the reconstructions with P jja simulations from a coupled atmosphere–ocean–sea ice general circulation model (the Kiel Climate Model, KCM). The results of cross-validation tests for the transfer functions show that both the WA-PLS model ( r 2 = 0.83, root mean square error of prediction (RMSEP) = 112.11 mm) and the Bayesian model ( r 2 = 0.86, RMSEP = 107.67 mm) exhibit good predictive performance. We stack all P jja reconstructions from northern China to a summary curve. The stacked record reveals that P jja increased since 9500 cal. yr BP, attained its highest level during the Holocene summer monsoon maximum (HSMM) at ~7000–4000 cal. yr BP and declined to present. The KCM output and the reconstructions differ in the early-Holocene (~9500–7000 cal. yr BP) where the model suggests higher P jja than the reconstructions. Moreover, during the HSMM, the amplitude of the P jja changes (~20–60 mm above present) in simulations is lower than the reconstructed changes (~70–110 mm above present). The rising (declining) P jja patterns in reconstructions before (after) the HSMM are more pronounced and fluctuating than in simulations. Other palaeohydrological data such as lake-level reconstructions indicate substantial monsoon precipitation changes throughout the Holocene. Our results therefore show that the KCM underestimates the overall amplitude of the Holocene monsoon precipitation changes.