[M-IS16] Paleoclimatology and paleoceanography

[MIS16-P07] Sphagnum and grass cellulose oxygen isotopes in peat cores reveal climate changes in northern Japan over the past 4400 years and close relationship with human histories

*Masanobu Yamamoto¹, Osamu Seki² (1.Faculty of Environmental Earth Science, Hokkaido University, 2.Insititute of Low Temperature Science)

Keywords:cellulose oxygen isotopes, Holocene, Climate

The cellulose δ¹⁸O of plant tissues in peat is a potential climatic proxy to understand the atmospheric dynamics of the past. In this study, we analyzed the δ¹⁸O values of sphagnum and vascular plant cellulose in 4.6- and 4-m long peat cores from the Minamihama moor in Rishiri Island, Japan, to understand paleoclimate changes in northern Japan over the past 4400 years. Cellulose δ¹⁸O of sphagnum showed multi-centennial and millennial variation with higher values in 4500–3400, 2800–2300, and after 700 year BP, and lower values around 3000, and 2200–1000 year BP. The difference of δ¹⁸O between vascular plants and sphagnum (Δδ¹⁸O_vp–sp), a proxy of relative humidity, was reversely correlated with δ¹⁸O, indicating humid climate in the periods with higher sphagnum δ¹⁸O. The factors controlling the climate in Rishiri Island changed between 2800 and 1300 years BP. In the older period, the development of the North Pacific High determined the climate of entire Hokkaido area via changes in the position of the westerly jet and the East Asian summer monsoon rainfall. In the younger period, this mechanism continued to determine the climate of eastern Hokkaido facing the Pacific Ocean, while the intensity of the Tsushima Warm Current determined the climate in Rishri Island. The weakening of the North Pacific High shifted the westerly jet south of Rishiri Island so that the position of the westerly jet did not influence the precipitated water δ¹⁸O in the Rishiri Island. The climate changes in Rishiri Island corresponded to the evolution of human culture in Hokkaido Island.