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Keiji Takemura, Kyoto University (Japan)
Masaaki Okuda, Natural History Museum and Institute, Chiba (Japan)
Takeshi Nakagawa, University of Newcastle (United Kingdom)
Akira Hayashida, Doshisha University (Japan)
Philip, A. Meyers, University of Michigan (United States)
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Lake Biwa is the largest and oldest lake in Japan. Whereas the neibouring basin Lake Suigetsu has varved sediments of the past 150 kyr, Lake Biwa has continuous sediments of a million year age. Therefore coupling of the two basin works will permit understanding on the Quaternary climate and tectonics in multi time scale. Deep drilling for Lake Biwa commenced in the 1970's, and the drilled core in 1982-3 (i.e., the 1400 m core) has revealed ∼900 m muddy sediments overlying the basement rock.. In 2005, the doubt on discontinuity of the sequence in present Lake Biwa was completely cleared. Improvements on fission track timescale have successfully identified the paleomagnetic reversal near the base as Jaramillo rather than Olduvai, determining time coverage of the Lake Biwa sediment as ∼1.5 Ma. A highly linear SAR (Sediment Accumulation Rate) curve is thus given to the 900 m-deep Lake Biwa sediment. This secures the stable sedimentary environment of the basin, and the significance of Lake Biwa sediment as a good recorder for paleoclimate changes. Moreover, progress in the Japanese tephrochronology in recent decades has provided marker tephras in and around the basin. Lake Biwa is, therefore, an ideal terrestrial site to explore paleoclimate and tectonic history during the past 1 Ma of East Asia. Providing examples of paleomonsoon variations will improve our knowledge on the present monsoon drive mechanism by examining the interaction to the Earth's internal forcings, which would aid future climate projections. Searching for substitutes of marine δ18O from lacustrine records will integrate the separatively accumulated paleoclimate records in lacustrine and marine realms, enabling an improved picture on global climate change. Collecting paleoearthquake evidence before the historical period will provide insight to the coming great earthquake. This project will produce detailed and well-dated paleoclimate and seismic records of the past 1 Ma, by performing a 900 m-long new drilling penetrating Lake Biwa sediment, Japan. Multidiscipline approaches of pollen, diatom, alkenone, inorganic geochemistry and paleomagnetic analyses will realize the above research scopes, for contributing to the loading issues that the Japanese and world societies now highly concerns.
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