Abstract
A large number of ice-rafted debris (IRD) have been found in the MD179 cores of the Japan Sea from off Joetsu to off Okushiri Island. The IRD appear in the MIS 5.4 when the last inter-glacial period passed, and occur most abundantly during the MIS 2. The occurrence of IRD in the sediments of off Joetsu indicates floated ice had commonly appeared in the further southern part of the Japan Sea than the area the former studies have expected.
Basalt lava is the most common lithology among the collected IRD, and black siliceous mudstone or chert follow it. The roundness of IRD reveals the IRD-bearing ice was not originated from on-land glacier but from sea ice formed on sea shore. The sea ice has been expected to come from southern part of the Sikhote-Alin area of the Asian Continent across the Japan Sea (Ikehara, 2003), but the lithology of IRD indicates the coast along the Japanese Islands is not precluded from the provenance area. The high frequency of IRD in the sediment of off Joetsu during the MIS 2 strongly suggests the floated ice had arrived in the further southern part of the Japan Sea. The formation and melting of sea ice in a wide area of the Japan Sea should have had a great influence on the environment of the Japan Sea and the surrounding land areas.
