HOLOCENE CLIMATIC CHANGES AND ENVIRONMENTAL HISTORY OF ITURUP ISLAND, KURILE ISLANDS, NORTHWESTERN PACIFIC

Abstract

The study of Holocene deposits on Iturup Island is very important for understanding palaeolandscape changes on the island. It is separated by deep straits from the neighbouring islands and was isolated during the last glacial maximum. Landscape changes over the last 40000 years and the role of refugia on vegetation development are discussed. Changes in natural processes in this region were controlled both by global climatic changes and by regional factors. Birch forests developed at the warming about 36-37 ka ago, whereas tundrapark landscape developed with the cooling of the last glacial maximum. Holocene environments reflect climatic changes and sea-level oscillations. The fluctuation of warm and cold currents influenced the landscape development. At the Holocene Optimum (about 6 ka) broadleaved forests with Quercus, Phellodendron, Carpinus, Juglans, Fagus, Fraxinus and Syinga occupied the Okhotsk side of central Iturup. Climate was warmer than present and the sum of active tempe]ratures (Σt ≥10°C) was not less than 1800°C. The warming was coincident with the transgression with the highest sea level up to 3.5 m above present sea level (PSL). Numerous coastal lakes were formed at this time. A shallow strait occurred on the low Vetrovoy isthmus. The sea-level drop at 4700-4500 radiocarbon years BP led to the development of large dunefields only within bays with a flat coast due to the supply of sandy material from the inshore drainage zone. At the beginning of the late Holocene about 4000 BP the vegetation changed very little due to the warm current influence. Cool-temperate forests with dominant Quercus had a wide distribution, but the diversity of broadleaved genera decreased. A minor transgression occurred about 4100-4000 BP with a sea-level rise on about 2.5 m above PSL. Active accumulation of deposits took place in the coastal zone at this time. Great vegetation changes and climatic deterioration took place in the last 2000 years BP. Cool-temperate broadleaved forests were confined to the Okhotsk side of the central island. Grasslands and swamps also developed in the coastal lowlands at this time. A minor regression led to the formation of large dunefields. Isthmuses increased and coastal wetlands with lakes formed. The presence of marine diatoms in floodplain lake deposits indicates a sea-level rise at about 1060 ± 60 BP. At this time warming was not intensive, but was well pronounced. The last phase of active aeolian accumulation took place during the ‘Little Ice Age’ cooling and regression.