北日本における最終間氷期以降の古気候の復原

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  • The Reconstruction of the Paleclimate in Northern Japan since the Lastinterglacial

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Complete and high-resolution pollen records in the last interglacial-glacial cycle are not yet obtained in Japan. The aim of this paper is to show the detailed paleoclimatic features of the last interglacial-glacial cycle by synthesizing the pollen records obtained from the terrace deposits of different places and different ages. The Hidaka district is one of the most successively developed areas of marine and fluvial terraces in Japan. Many samples for pollen analysis were collected from those terrace deposits. The stratigraphical sequence of the samples was mainly determined by the tephra layers which were intercalated in the terrace deposits and were dated by various methods. Five climatic types, glacial maximum(GM), glacial sub-maximum(GM'), glacial(G), lateglacial (LG), and postglacial(PG), were classified as a criterion for the zoning of pollen assemblages based on the pollen records of Kuromatsunai, southwestern Hokkaido and Sakhalin obtained by Sakaguchi(1989). The synthesized results are shown in Fig.6. the reconstructed paleoclimate coincides closely with the normalized oxygen-isotope curve which is proposed by Martinson et al. (1987). Two warm stages around 120kaBP and 90-100kaBP and two relatively warm ones around 80 kaBP and 50-60kaBP, are recognized in the Hidaka district. According to the normalized oxygen-isotope curve, isotope stage 5e is suggested to be warmer than isotope stages 5c and 5a. But in the Hidaka district, warm periods correlated to isotope stages 5e and 5c are considered to be the same level. Two very cold periods around 60kaBP and 20kaBP, which correspond to isotope stages 4 and 2,existed in this district and were not different in coldness. On the other hand, two cold periods in isotope stage 5 (stages 5d and 5b) were not so cold. It is coincident with the paleoclimate inferred from the oxygen-isotope curve.

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