Terrestrial—oceanic environmental change in the southern Okhotsk sea during the Holocene

Abstract

The Okhotsk Sea plays a significant role in climatic and oceanic environmental change on regional and global scales. The fluctuation in pollen and spores abundances was investigated in order to reconstruct terrestrial and ocean environmental change during the Holocene. Fluctuation of the total abundance and assemblage of most of pollen and spores reflects terrestrial environmental change along the coastal area of the southern Okhotsk Sea. On the other hand, the abundance of Cryptomeria, Cyclobalanopsis and Castanopsis pollen from plants which are not currently growing in Hokkaido, is suggested to be a good proxy for the intensity of the Tsushima Current. Relatively warm pollen assemblages characterize Periods 1 (calendar age 7240–3050 yr BP) and 3 (150–0 yr BP) while a relatively cold pollen assemblage characterizes Period 2 (3050–150 yr BP). Three warm sub-periods 1a (7240–6500 yr BP), 1c (5900–4550 yr BP) and 1e (4300–3550 yr BP) are associated with relatively strong intensity of the Tsushima Current, transgression, and the occurrence of bivalves living in warm conditions. Continuous cooling started 3000 yr BP. The area remained so cold that the intensified Tsushima Current (2800–2400 and 1700–1400 yr BP) would have made little difference to terrestrial warming in the southern Okhotsk Sea. In the uppermost samples, a large increase in total abundance of pollen and spores may be partly attributed to the modern global warming effect.