Spatial variations of monsoonal rain in eastern China: Instrumental, historic and speleothem records |
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| Authors: | Nai-Jung Wan Hong-Chun Li Zi-Qi Liu Hsin-Ying Yang Dao-Xian Yuan Yong-Heng Chen |
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| Institution: | a Department of Earth Sciences, National Cheng-Kung University, Tainan 70101, Taiwan, ROC;b Department of Geosciences, National Taiwan University, Taipei 106, Taiwan, ROC;c School of Geographical Sciences, Southwest University of China, Chongqing 400715, China;d School of Environmental Science & Engineering, Guangzhou University, Guangzhou 510006, China |
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| Abstract: | We select four caves and their nearby cities in the monsoonal region of China for studying the relationships among precipitation, temperature, summer monsoon intensity and stalagmite δ18O. The instrumental, historic and stalagmite δ18O records from these areas show strong spatial disparities on annual to decadal scales, so that climatic conditions in a single location cannot represent these of the entire eastern China. On time scales <500 years, stronger summer monsoon may lead to higher rainfall in some locations but not over eastern China. Correlation between the summer monsoon strength and precipitation is not only location-dependent but also changes with time. One may not use the paleoclimatic pattern of cold–dry and warm–wet on glacial/interglacial ages throughout all time scales for climatic conditions in the monsoonal region. On centennial to millennial scales, stalagmite δ18O variation trend from eastern China resemble solar irradiance with lighter δ18O corresponding to increased solar irradiance, and vice versa. The similar trends may reflect climatic feedbacks link to solar forcing to cause changes in the summer monsoon intensity and/or in monsoonal circulation. Changes in monsoonal circulation and intensity affect (1) summer rainfall intensity, (2) summer/winter precipitation ratio, or (3) ratio of moisture from Indian/Pacific oceans, or a combination of the three. Thus, a speleothem δ18O record may not be proper to be used as a proxy of paleo-precipitation amount, especially on short time scales. Based on the four stalagmite δ18O records during the last 2000 years, EASM strength decreased from AD 200 to AD 500, and from AD 1300 to AD 1600 (the 1st half of the Little Ice Age), whereas EASM strength increased from AD 1600 to AD 1900 (the 2nd half of the Little Ice Age). The EASM strength has weakened since early 1900’s. |
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| Keywords: | East Asian Monsoon Monsoonal climate Speleothem δ 18O Eastern China |
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