Geomagnetic relative paleointensity chronostratigraphy of sediment cores from the Okhotsk Sea
Abstract We conducted a paleomagnetic study of three piston cores from the central Okhotsk Sea to enable inter-core correlation and age estimation using relative paleointensity of the geomagnetic field, which can provide the basis for paleoceanographic studies in this area. The cores are composed of diatom-bearing dark olive gray silty clay. Magnetic overprints were generally removed by alternating-field demagnetization of up to 10 mT. Magnetic properties reveal no evidence of reductive diagenesis or magnetite dissolution. The anhysteretic remanent magnetization (ARM) was used as a normalizer for relative paleointensity estimations, because there is a smaller coherence between normalized intensity and the ARM than with saturation isothermal remanent magnetization (SIRM). Depths of the three cores were converted to ages by correlating relative paleointensity variations with those from Ocean Drilling Program Site 983, which was selected as a target curve because of its higher resolution than the widely-used Sint-800 paleointensity stack. The age at the bottom of the cores is estimated to be between 360 and 540 ka. Inter-core correlation using relative paleointensity variations reveals that changes in magnetic properties such as magnetic susceptibility and magnetic mineral grain size are not synchronous between the northernmost site and the southern two sites despite their close proximity, which indicates regional differences in paleoenvironmental variations associated with glacial–interglacial changes. Nevertheless, relative paleointensity variations among the three cores are mutually consistent, and agree with other published paleointensity curves, which indicates that our paleointensity records are not influenced significantly by lithological changes.