HR: 1340h
AN: GP43B-0858    [Abstracts]
TI: Relative paleointensity variation during the last 300 kyrs in the Northwestern Pacific region
AU: * Yamamoto, Y
EM: yuhji-yamamoto@aist.go.jp
AF: Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Yamazaki, T
EM: toshi-yamazaki@aist.go.jp
AF: Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Kanamatsu, T
EM: toshiyak@jamstec.go.jp
AF: Program for Deep Sea Research, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Mishima, T
EM: mishima@gaia.h.kyoto-u.ac.jp
AF: Graduate school of Human and Environmental Studies, Kyoto University, Yoshida Nihonmatsu-cho, Sakyo-ku, Kyoto, 606-8501 Japan
AU: Aoki, K
EM: aoki-kao@aist.go.jp
AF: Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AB: We have obtained 8 relative paleointensity records from gravity and piston cores collected from the Northwestern Pacific Ocean (33N-39N/146E-159E). The gravity cores consist of NGC108 (6.5m, 3390m), NGC109 (6.5m, 4530m), CGC12 (4.4m, 5600m), and CGC16 (4.2m, 5670m), whereas the piston cores comprised of KR0215-PC2 (11.7m, 5936m), KR0215-PC3 (18.8m, 5970m), KR0215-PC7 (17.6m, 5750m), and MR01K02-PC1 (11.5m, 5758m). Although most of the water depths of these cores are below the Calcium-carbonate Compensation Depth (CCD), oxygen isotope records are available for two cores, NGC102 (last 300 kyr, Kawahata et al., 1999) and NGC108 (last 180 kyr, Maeda et al., 2002). NGC102 (3.3m, 2612m) was obtained in the vicinity of the studied cores. The present cores showed large decrease in S-ratio (-0.3T) at several horizons. This suggests that magnetic minerals were dissolved at these depths. Hence, we excluded such intervals from the normalized intensity records. Then the depth of each core was converted to a common depth scale of KR0215-PC3 using magnetic susceptibility. They were further transformed to ages based on the oxygen isotope stratigraphy. The age estimation is supported by two ash layers identified as Aso-4 (86-90ka) and Ata-Th (240 ka) in MR01K02-PC1. The resultant relative paleointensity curves commonly showed lows and highs at similar ages, though their amplitude did not necessarily agree among the curves. There are not only well-known lows around 40 ka (Laschamp), 120 ka (Blake) and 190 ka (Icelandic basin) but also other minima around 60 ka, 80ka, 160ka and 240 ka. Although further tuning may slightly shift these ages, they are possibly associated with recently reported or unknown geomagnetic excursions.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1513 Geomagnetic excursions
DE: 1521 Paleointensity
DE: 1560 Time variations--secular and long term
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting