Sea-level Change from the 10th to 17th Centuries around Lake Saroma, Eastern Hokkaido

Abstract

Eastern Hokkaido is known to be the area where marker tephras for the historic ages are widely distributed. The authors analyzed the diatoms in the sediments which are intercalated between the tephras of Ma-b (Mashu-b volcanic ash erupted ca. 970) and Ko-c2 (Komagadake-c2 volcanic ash erupted in 1694), and tried to reconstruct the paleoenvironment of this area. The two peaks of marine and brackish diatoms suggest the two stages of high salinity (late 10th-11th century and late 14th-late 16th century). Such salinity changes during the period from the 10th to 17th centuries seem to be phenomena corresponding to the cycles of transgression and regression that accompanied climatic changes.