Orbital-scale vegetation-ocean linkages in western Japan during the last 500,000 years based on a new pollen record from the Japan Sea

Climate and vegetation in Japan are strongly affected by the East Asian monsoon and the Japan Sea environment. We are studying the terrestrial ecosystem response to climate changes influenced by those atmospheric and oceanic environments based on pollen records from Japan Sea and terrestrial sites around the Japanese archipelago. In this presentation, orbital-scale vegetation fluctuations during the last 500,000 years will be discussed based on a new pollen records from the U1427 sediment core at the northern coast of western Japan, which was drilled by Integrated Ocean Drilling Program (IODP) Expedition 346.

Pollen record from the U1427 site indicated that cold-cool conifers such as Picea, Tsuga and Pinus subgenus Haploxylon were dominant during the glacial periods in the last 500,000 years. In the interglacial periods, temperate deciduous broadleaved trees such as Quercus subgenus Lepidobalanopsis and Fagus became dominant with warm temperate evergreen oaks. However, the evergreen oaks only showed relatively high percentages during MIS 11 and the Holocene, in contrast with the other interglacials. During transient times between the interglacial to the glacial,temperate conifer of Cryptomeria japonica increased alternating with temperate deciduous broadleaved trees, correlated with orbital-scale insolation changes. Compared based on the tephra stratigraphy, fluctuations in the pollen record from the U1427 were quite similar to those from Lake Biwa in western Japan.

Compared with marine environmental proxy records from the U1427, cold-cool conifer forests became dominant during the glacial periods when surface-freshening occurred in the Japan Sea influenced by the lowest sea level and the isolation from the East China Sea. In contrast, temperate deciduous broadleaved forests associated with evergreen oaks developed in the interglacial periods when the Tsushima Warm Current flowed into the Japan Sea. However, terrestrial vegetation had started to change before those extreme ocean events. It suggested that primary factors for terrestrial ecosystem changes were atmospheric climate conditions such as the East Asian Monsoon, although those extreme conditions in the Japa_­­­n Sea enhanced the developments of dominant forests in the glacials and the interglacials.