A Geomagnetic Secular Variation Record for the Last Glacial Period, Reconstructed from Coastal Bog Sediments on the Inland Sea of Japan.

Abstract

A paleomagnetic secular variation record of geomagnetic field direction for the time span from 25 to 16ka was obtained from oriented bog sediment samples in a coastal area of the eastern Inland Sea, Japan. The plot of this secular variation record, combined with Holocene secular variation data, shows that a long-term westerly declination feature began after 16ka and ended at 7.5ka. This feature lasted more than 4, 000 years and less than 8, 500 years. The declinations at 25-16ka are dominated by easterly values, and no westerly declination was observed in the time span of 24-19.5ka. The inclinations at 25-16ka are characterized by slightly shallow values with small amplitude changes, compared to those in the Holocene. Prior to 18ka a large clockwise looping was dominant in the motion of the geomagnetic vector, while counter-clockwise rotations were dominant after it. Many features of secular variation in the last glacial period have the potential to yield good age constraints for use in paleomagnetic dating.