Earth Planets Space, Vol. 59 (No. 7), pp. 795-805, 2007
Yukiko Yokoyama1, Toshitsugu Yamazaki2, and Hirokuni Oda2
1Department of Biosphere-Geosphere System Science, Faculty of Informatics, Okayama University of Science, Japan
2Geological Survey of Japan, AIST, Higashi, Tsukuba, Japan
(Received October 27, 2006; Revised May 1, 2007; Accepted May 26, 2007; Online published July 20, 2007)
We have analyzed three sets of paleointensity series varying in duration from 300 to 1600 ka to confirm the existence of paleosecular variation on a 100-ky time scale. The data series are from sediment cores in the equatorial and North Pacific regions. We transformed the three time series into wavelet space and found characteristic variations in a 100-ky time scale. We also calculated wavelet correlation between the series of the paleointensity and rock magnetic parameters of each core to assess the efffect of rock magnetic properties on relative paleointensity. The wavelet correlation coefficients of the three cores are small, so the change in the paleointensity in each core is concluded to be independent of magnetic properties. In order to confirm the cause of the paleointensity variation, we calculated the wavelet correlation among the three cores. The relative intensity variations of the three cores are significantly correlated, while rock magnetic parameters are not, indicating that there are differences in rock magnetic variations among the cores, although they appear to occur on similar scales. On the other hand, all sets of relative paleointensity have synchronous variations. Such paleointensity variations observed over a wide area are considered to originate from changes in the Earth's magnetic field.
Key words: Paleosecular variation, paleointensity, geodynamo, Earth's orbit, excentricity, geomagnetic field, secular variation.