Biohistory Jyournal, Summer, 2004

Research: Index > The relationship between the environment and civilization and the near future told by annual laminated sediment sequence

Narrative science The relationship between the environment and civilization and the near future told by annual laminated sediment sequence

Yoshinori Yasuda, International Research Center for Japanese Studies

The diatoms in early spring and clay minerals in fall and winter gently settle on lake bottoms to form the yearly layers called varves. Japan has four distinct seasons and very distinct changes in water temperature, so these are quite suitable for forming the varves. These conditions are very favorable for the people who conduct research the relationship between civilization and the earth's environment in the past using varves.     We discovered the first annual laminated sediment sequence in Asia and the longest consecutive varve recorded in the world at 100,000 years at Lake Suigetsu in Fukui Prefecture. These sedimentation layers were later discovered throughout Japan, and we were able to discern the relationship between the environment and civilization from the varve in Megata, Akita Prefecture.     The Bohai kingdom that stretched from northeast China to the northern part of the Korean peninsula flourished until it crumbled in 926. The cause is said to have been the large eruption of Mt. Paektusan. Incidentally, an analysis of the varves shows that Mt. Paektusan had a major eruption in 937. Also, an analysis of the type of diatoms in the varves shows a cooling of the climate for three years before Bohai's fall. It is possible that Bohai collapse was due in part to damage from the frigid temperatures when the climate cooled.

Which came first: The eruption of Mt. Paektusan or the collapse of Bohai?
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There was a major shift in the earth's climate about 15,000 years ago from an ice age to a postglacial age. Recreating the earth's environment in yearly units using varves shows that monsoon Asia's air temperatures rose roughly 500 years before those in Europe and the polar regions. It also reveals that the response of the ecological system in Monsoon Asia predated the other by 3000 years. In short, climate changes differ by time and region.

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The varves near the sites of human habitation will likely yield important data on the impact the climate changes in different regions had on human beings. Analysis using varves has fewer errors than the C measurement methods, and the varves can verify the relationship between the environment and people in the recent past. We are conducting research in the belief that it also will be possible to use this method for forecasting the near future.

Yoshinori Yasuda     Born in 1946, Yasuda was awarded a doctorate from the Tohoku University Graduate School of Science. After serving as an assistant in Hiroshima University's Faculty of Integrated Arts and Sciences and as an assistant professor at the International Research Center for Japanese Studies, he was named professor at the latter institution. He also has served as visiting professor at Reitaku University, Humboldt University in Germany. He holds the addition post of professor in the Kyoto University Graduate School of Science.

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