Palynological Study on Core Samples from Lake Biwa-ko

In this paper, the present writer deals with the change of paleoclimate of Lake Biwa-ko during the past 0.6 million years. The purpose of the writer is to clarify paleoclimate and to establish the late Quaternary chronology which is comparable to European and American chronological time-tables, from the viewpoints of paleontological and chemical studies of the present core samples of nearly 12 meters and 200 meters in length. On the basis of palynological study, though temperature during the late glacial age is regarded as several degrees in centigrade lower than the present one, the temperature during the Flandrian transgression of the Postglacial age is about two degrees in centigrade higher than the present one. The analysis of the 200 meters core sample showed that most of the samples contained fossil pollen grains and/or spores of about 40 genera and/or families. As a result of the analysis of the pollen and spore assemblages, ten cold climatic stages (co-1, co-2, ……, co-10) were recognized throughout the boring core. In the same core, warm climatic stages (w-1 and w-2) were found two times including the Postglacial climatic optimum. It is true that the warm climatic stage shown by the abbreviation w-1 and cold climatic stage shown by co-1 in Fig. 2 are correlated with the Atlantic age and the last stage of the Würm glacial age respectively. On the basis of pollen analysis of about 12 meters core sample, the pollen grains of Oryza are found in the samples of 0-3.4 meters below the present lake bottom as shown in Fig. 4. Judging from the radiocarbon dating, the horizon of 3.4-3.7 meters deep is inferred to be about 2, 900 3, 000 years before the present. In addition, many grass pollen grains and spores are also found in the samples of 0-3.7 meters (about 3, 000 years B. P.). Their frequency in the above-mentioned horizons is higher than that of the other horizons. Such phenomena of the ancient flora indicate an influence of ancient man upon natural vegetation in the latest Jomonian and/or early Yayoian period.