To confirm the influence by the global climatic changes and sea level fluctuations to lake environment, we obtained undisturbed vertical core sections of sediments using drilling equipments at several brackish lagoons in Japan. The diatom-inferred salinity reconstruction for these brackish lagoons provides an excellent example of long-term salinity measurements during the Holocene.
At Lake Hamana and Lake Kasumigaura, a series of environmental oscillations with 700-1200 years intervals between fresh water, brackish to marine episodes followed after the eruption of Akahoya Ash (6300y. BP). They have presumably varied substantially due to sea level fluctuations within the Late Holocene.
On the other hand, at Lake Shinji, a very closed tidal flat, where diatom valves are rarely preserved in sediments, continued for thousands of years after the eruption of Akahoya Ash (6300y. BP).