Variations in monsoonal rainfall over the last 21 kyr inferred from sedimentary organic matter in Tung-Yuan Pond, southern Taiwan Tien-Nan Yang a, * , Teh-Quei Lee a , Philip A. Meyers b , Sheng-Rong Song c , Shuh-Ji Kao d , Ludvig Löwemark e , Rou-Fei Chen a, f , Huei-Fen Chen g , Kuo-Yen Wei c , Cheng-Wei Fan h , Liang-Jian Shiau a, g , Hong-Wei Chiang c , Yue-Gau Chen c , Min-Te Chen g a Institute of Earth Sciences, Academia Sinica, Taipei 115, Taiwan b Department of Earth and Environmental Sciences, The University of Michigan, Ann Arbor, MI 48109-1005, USA c Department of Geosciences, National Taiwan University, Taipei 106, Taiwan d Research Center for Environmental Changes, Academia Sinica, Taipei 115, Taiwan e Department of Geological Sciences, Stockholm University, Stockholm 10691, Sweden f Department of Geology, Chinese Culture University, Taipei 111, Taiwan g Institute of Applied Geosciences, National Taiwan Ocean University, Keelung 202, Taiwan h Department of Earth and Environmental Sciences, National Chung Cheng University, Chia-Yi 621, Taiwan article info Article history: Received 17 January 2011 Received in revised form 28 August 2011 Accepted 30 August 2011 Available online 19 September 2011 Keywords: Atomic TOC/TN ratio East Asian summer monsoon Holocene Thermal Optimum Paleorainfall intensity Taiwan Younger Dryas abstract Changes in paleorainfall intensity linked to the strength of the East Asian (EA) summer monsoon since 21 cal kyr BP are inferred from the organic matter contents of a 15-m sediment core from Tung-Yuan Pond in southern Taiwan. High total organic carbon/total nitrogen (TOC/TN) values in association with increased TOC content suggest that more soil-derived material containing terrestrial organic matter (OM) was delivered to the lake during periods of increased runoff associated with extensive precipitation that resulted from intensified summer monsoons, whereas low values indicate OM possessing a dominant algal origin during weakened summer monsoons. Rainfall intensity in terms of the proportion of terrestrial OM was high in four periods: the last deglaciation (w17.2 to w12.2 ka), the early Holocene (w10.6 to w8.6 ka), the middle Holocene Thermal Optimum (w7.7 to w5 ka) and the late Holocene (w4.2 to w2 ka), whereas it was low in the intervening time periods. High TOC/TN values coincide with peak values of summer insolation, and thus the strongest EA summer monsoon during the early and middle Holocene; small drops in these ratios correspond to increasing and decreasing solar radiation in the deglacial period and the late Holocene, respectively. The four intervals with low TOC/TN ratios, as well as episodic drops of the ratios during the deglaciation and the early and late Holocene are concordant with the late last glacial (w21 to w17.2 ka), the Oldest (w14.8 ka), the Older (w13.3 ka) and the Younger Dryas (w13 to w11.5 ka), the 8.2 cold event (w8.6e7.7 ka) and a late Holocene cold event (w5e4.2 ka), and suggest a weakened EA summer monsoon during these times. Moreover, high frequency hydrological variability occurred during the early Holocene, heavy rainfall persisted during the middle Holocene, and precipitation intensity generally diminished after w5 ka. The Tung-Yuan Pond sediment record indicates that the TOC/TN ratio can be used as a paleorainfall intensity proxy to trace variations in the EA summer monsoon strength in other small lakes. Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. 1. Introduction Unpredictable variations in precipitation, which can lead either to flooding or to limited water availability, create serious challenges for human society, especially for the dense populations in eastern and southeastern Asia. It is therefore important to better understand modern and past rainfall variations in order to improve predictions of the impacts of future climate changes. Toward this end, many studies of the monsoon-related changes in precipitation in eastern Asia have been performed (e.g., Feng et al., 1999; An, 2000; Wang et al., 2001; Xiao et al., 2006; Chen et al., 2007; Zhou et al., 2007; Yang and Scuderi, 2010). These studies generally reveal past mois- ture patterns that were paced by the orbital evolution of solar activity. In addition, some other studies describe the multi-decadal rainfall variation in Asia and North America from lacustrine records * Corresponding author. Tel.: þ886 2 27839910x412; fax: þ886 2 27839871. E-mail address: tnyang@earth.sinica.edu.tw (T.-N. Yang). Contents lists available at SciVerse ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev 0277-3791/$ e see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2011.08.017 Quaternary Science Reviews 30 (2011) 3413e3422