ENVIRONMENTAL CHANGES DURING THE LATE QUATERNARY IN TAIWAN AND ADJACENT SEAS : AN OVERVIEW OF RECENT RESULTS OF THE PAST DECADE ( 1990-2000 )

This review article reports the major progress of our understanding of the past environmental changes during the late Quaternary in Taiwan and its adjacent marginal seas. Long giant piston cores obtained from the South China Sea have provided continuous paleoceanographic records in high resolution regarding the Asian monsoon, Western Pacific Warm Pool and sea-surface temperature changes for the late Quaternary. Hydrological conditions of the South China Sea have been modulated mainly by orbital forcing at 100-, 41and 23-kyr periodicity during the past 350 thousand years (kyrs). Sea surface temperatures fluctuated by at least 4C between glacial and interglacial periods and show strong cyclicity of 23 thousand years over the past 400 kyrs. Millennial variations comparable to those found in Greenland ice core and North Atlantic were documented from various proxies for the past 150 kyrs, implying a close teleconnection between Taiwan/adjacent seas with Greenland and North Atlantic. Pollen and chemical analyses of cores taken from lakes allowed reconstruction of the paleoenvironmental changes during the past 20 kyrs on Taiwan. The last glacial period prior to 15 thousand years ago (ka) was characterized by cold and dry climates. The climatic amelioration responding to the deglaciation transition of the global climate took place between 15-10 ka. A short-lived reversal to a cold and dry climate corresponding to the Younger Dryas Event was evident from both marine and terrestrial records. The environment of the last 10 kyrs (the Holocene Epoch) has been relatively constant but kept fluctuating until 2500 years ago when the condition became the present one. Warm and wet climates prevailed during 9.7-7.1 ka, 6.2-5.5 ka and 2.5-1.5 ka 150 Western Pacific Earth Sciences, Vol.2, No.2 whereas a distinctive cold spell might have occurred between 5 to 3.5 ka. Conditions have fluctuated over the past 2500 years in response to the global Medieval Warmth and Little Ice Age.

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