Climatic Change since the Late Pleistocene in the Japanese Islands: The Role of the Tibetan Plateau and West Pacific Warm Water Pool : The Role of the Tibetan Plateau and West Pacific Warm Water Pool

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Paleoclimate researchers have come to believe that the North Atlantic was much better placed than the tropics to play an important role in climatic changes during the most recent glacial period. Since 1990, paleoclimate data from Greenland ice cores have pointed to that region as the site of the most dramatic and abrupt climatic shifts. These climatic shifts of the last glacial age created sensitive turning points on the thermohaline conveyer belt, which became prime movers of global climate. However, new data for the past SST based on alkenone unsaturation ratios of the tropical Pacific have given us much information on the tropics as a strengthening cooler during the last glacial. Also, high resolution analysis of isotopes in the Antarctica ice core, based on correlation of methane concentration changes, has provided strong evidence for asynchronous temperature changes in Greenland and Antarctica during the Last Glacial.These paleoclimatic interpretations have led us to investigate whether there was a lead and lag relationship in the onset and end of warming or cooling among the North Atlantic, Antarctica, and tropical Pacific regions.We carried out sampling of varved lacustrine sediments and loess-paleosols in East Asia and have subjected the samples to in high-resolution analysis since 1995. Our research will provide information on the question of whether the warm pool of the western Pacific is a triggar of climatic changes or not, because Asian monsoon intensity is controlled by the magnitude of SST in the West Pacific warm water pool and by the snow cover on the Tibetan Plateau in the winter season.We investigated changes of eolian dust flux calculated from accurate sedimentation rate on the base of varve counting in Lake Suigetsu varve and fluvial detrital quartz flux in Lake Suwa sediment. Illite is one of the main components of clay minerals in recent eolian dusts and loess-paleosol of the Chinese Loess Plateau. Time-series changes indicate that decreasing dust flux due to expansion of vegetation cover in dust source areas has occurred since 15, 500 years BP. Organic carbon flux due to increasing primary production in surface water has increased in Lake Suigetsu since about 16, 000 years BP. However, stratified water mass in summer in Lake Suigetsu has been stable since 18, 000 years BP. In Lake Suwa, we clarified that there were high precipitation events can be correlated closely to deglacial events of the Asian monsoon. These evidence give us three important pieces of paleoclimatic information: 1) Warm and humid climate during the Asian summer monsoon expanded from Japanese Islands to the inland areas of China after 16, 000 years BP. 2) Abrupt onset of warming climate in inner areas of East Asia occurred earlier than that of the GISP2 ice core, with a time lags of more than 1, 000 years. 3) It possible to locate the trigger of global changes around the West Pacific warm water pool rather than in the North Atlantic.

Climatic Change since the Late Pleistocene in the Japanese Islands: The Role of the Tibetan Plateau and West Pacific Warm Water Pool : The Role of the Tibetan Plateau and West Pacific Warm Water Pool

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