The role of global and local factors in determining the middle to late Holocene environmental history of the South Kurile and Komandar islands, northwestern Pacific

Abstract

The study of Holocene deposits from northwestern Pacific Islands is very important for understanding the natural development of the area in the context of oceanic climate, strong microclimate variability, and the influence of contrasting marine currents. Holocene sections from Bering Island record the following events: cooling at about 4600–4500 yr BP; warming at about 3500–3400 yr BP; cooling at about 3000 yr BP; sea-level rise (up to 1.5 m) at about 2700 BP; cooling at about 1800–1400 yr BP; and sea-level rise at about 1000 yr BP. On the South Kuriles, a dry and cool climate changed to warm and moist about 7000–6500 yr BP, later than on Hokkaido Island. At this time, the Kuroshio Current system became more active and birch assemblages were replaced by cool–temperate broadleaf forests and mixed coniferous/broadleaf forests. At the Holocene Optimum (about 6000 yr BP), temperate broadleaf forest occupied almost all of Kunashir and the Okhotsk side of Iturup and the climate was warmer than present. The highest sea-level position reached was 2.5–3 m above present level about 6500–6300 yr BP. During the cooling about 4700–4500 yr BP, island vegetation changed slightly due to the influence of warm currents. Major sea-level regression during this period led to the formation of extensive coastal dune fields. The warming at the beginning of the late Holocene was almost as great as that of the Holocene Optimum. Two minor transgressions are recorded. The vegetation changes and climatic deterioration that took place in the second half of the late Holocene resulted in either a disappearance of thermophylous taxa or in a southward shift of their natural habitats. During the cooling from 1700 to 1300 yr BP, the isthmus area increased, coastal wetlands with lakes and coastal dunes with paleosols were formed, and grassland and swamp landscapes developed. Late Holocene warming was not intensive. Volcanic impact on environments led to changes in vegetation assemblage, swamping of the area, and thick soil profile formation.