[H-QR04] Quaternary, Diachronic dynamics of human-environment interactions

[HQR04-07] The preliminary study about vegetation change associated during the Jomon transgression based on a pollen analysis of a Lake Harutori sediment core, eastern Hokkaido

*Keisuke Sakai¹, Toshimichi Nakanishi², Toshiyuki Fujiki³, Futoshi Nanayama⁴, Ken'ichi Ohkushi¹ (1.Graduate School of Human Development and Environment, Kobe University, 2.Museum of Natural and Environmental History, Shizuoka, 3.Department of Applied Science, Faculty of Science, Okayama University of Science, 4.National Institute of Advanced Industrial Science and Technology )

Keywords:Jomon transgression, Pollen, Paleoenvironment

In the post-last glacial period of the Japanese archipelago, the mid-Holocene, about 7,500 to 5,000 years ago, is estimated to have been a warm period with temperatures about 2°C and sea levels 2-3 m higher than at present (Matsushima, 2006). The sea-level rise observed in the middle Holocene is called the Jomon transgression. Because the peak of the Jomon transgression may have been warmer than the present, it is attracting attention in paleoenvironmental studies as an analog for predicting the transition of ocean current systems, climates, and ecosystems in environmental studies associated with future global warming. Based on the analysis of shell fossil assemblages from shell middens, it has been suggested that during the height of the Jomon transgression (about 6,500-5,500 years ago), more southerly species expanded their habitats to the north (Matsushima, 2006). This qualitatively suggests that the Tsushima Warm Current may have extended northward to eastern Hokkaido based on shell community composition. On the other hand, paleoenvironmental data with high temporal resolution on the northward propagation of the Tsushima Warm Current during the Jomon transgression in Hokkaido are scarce, and consistent results with other environmental indices have not yet been obtained. Quantitative paleoenvironmental data at high temporal resolution from sediment cores deposited continuously at high sedimentation rates will not only lead to more accurate predictions of environmental changes associated with global warming but will also clarify the relationship between climate and humans (Jomon people).
In this study, we are conducting fossil pollen and foraminifera analyses of lake sediments from Lake Harutori in Kushiro, Hokkaido, Japan, to quantitatively reconstruct the land and sea environments during the Jomon transgression. In this paper, we report the preliminary results of the fossil pollen analysis.
It has already been shown that this sample can be reconstructed for the past 8,500 years by radiocarbon dating. The results of fossil pollen analysis have shown that the samples corresponding to the peak of the Jomon transgression tend to be rich in Fagus. Fagus is a deciduous broad-leaved tree widely distributed in the temperate zone, and its northern limit is currently the Kuromatsunai lowland in Hokkaido. This suggests that the distribution of Fagus extended eastward from the present during the warm period of the Jomon transgression and that Kushiro City also experienced warming. Since this analysis is preliminary, we will add more data in the future to reconstruct the paleoenvironment during the Jomon transgression in more detail and quantitatively.