Investigation on trigger of Asian monsoon intesities by using lake, shallow-sea and loess sediments

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There are often well-preserved varved sediments in maar lakes of western Europe and brackish-water lakes of Japan. Many chronological and sedimentological studies for high-resolution reconstruction of climatic and paleoenvironmental changes since Last Glacial have been carried out by using these varves. In particular, accurate chronology and high-resolution changes of the paleoenvironment reconstructed by using varved sediments since 102,000 yrs BP at Lago Grande di Monticchio, Italy (Zolitschka and Negendank, 1999) and since 45,000 yrs BP at Lake Suigetsu, Japan (Kitagawa and Van der Plicht, 1998 ; Fukusawa, 1999) has attracted scientific attention in Quaternary research.We hope to investigate triggers and birth place of global climatic changes on ocean and atmospheric circulations. Because there are several big questions on global climatic system in earth science field. One of these questions is "Where have given first impact to climatic system as a trigger?" Blunier et al. (1998) sh … More ows interrelationships among ice core data in Greenland and Antarctica presenting. Abrupt climatic changes during Last Glacial in Antarctica ice core seem to go ahead of those in Greenland (Blunier et al., 1998). Now, place of dispatch on global climatic change are presumed 3 main sites by many researchers as follows ; North Atlantic as birth place of ocean belt conveyor, Antarctica as ice volume product area, and low latitude area of West Pacific as warm pool. Our research will give many information to discuss whether warm pool of western Pacific is birth place or not. Because Asian monsoon intensity are controlled by magnitude of sea surface temperature in low latitude area of West Pacific and of snow covered area on the Himalayan / Tibetan Plateau in winter season. Research of varved lacustrine sediments in East Asia will give many information to solve our questions through detection of Sediment flux (mg/cm 2yr). We calculated accurate and high-resolution sedimentation rate on the base of varve counting in Lake Suigetsu varve. According to eolian illite and quartz fluxes in varved sediments, decreasing of dust flux due toexpansion of vegetation in dust source area such as Chinese Loess Plateau occurred since 15,500 years BP. However, stratified water massin summer at Lake Suigetsu appeared since 14,000 years BP, because main componets of iron minerals transported from Mn-rich vivianaite to siderite. Also, Organic carbon flux due to increasing primary production in surface water have increased since about 16,000 years BP. These facts indicate that vegetation in the inland area of Asia expanded before primary production increased in Lake Suigetsu. Four paleodimate records are roughly similar, but not in detail. Abrupt decreasing of eolian dust flux occurred in varve sequence of Japan was more quickly than increasing of delta 1 80 changes in GISP2 in the onset of the Boiling warm period except Pre-Boreal, and also decreasing rate was more quickly in the onset of the Younger Dryas period. Organic carbon flux originating from primary productions by phytoplankton increased since 16,000 years BP, though warming in water mass of Lake Suigetsu. These evidences give us three important paleoclimatic information as follows ; 1)Warm and humid climate by Asian summer monsoon expanded from Japanese Islands to the inland area of China since 16,000 years BP. 2) Abrupt onset of warming climate in inner area of Asian Continent occurred more quickly than that of GISP2 ice core with time lags more than 1,000 years. 3) Trigger of global changes was located at low latitudes rather than high latitudes around Greenland ice sheet because of existence of climatic changes at low latitudes prior to at high latitudes. Also, third evidence supports Prof. Wang Linglang's theory (Wang et al., 1999) about birth place of climatic impact to global changes. His theory suggests that changes of warm pool in West Pacific gave initial impact to global changes. Less