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doi:10.2204/iodp.proc.303306.209.2009

Materials and methods

Sediment samples from Sites U1302–U1304 and U1308 used in this study were taken aboard the JOIDES Resolution during Expedition 303 using either 7 cm³ plastic cubes or 1 cm³ plugs (i.e., splits of the shipboard carbon samples).

One cube was collected per section for the measurements. Wet cube samples were used to measure natural remanent magnetization (NRM), low-field mass-specific magnetic susceptibility (χ), and anhysteretic remanent magnetization (ARM). NRM was measured with a 2G Model 760 superconducting rock magnetometer, and χ values were made with a Kappabridge KLY 3S at Kyoto University. Samples were given ARM in a steady direct current (DC) biasing field of 0.1 mT in a peak alternating field (AF) of 80 mT using a 2G Model 760 at the Geological Survey of Japan. ARM susceptibility (χ_ARM) is derived by dividing ARM by the bias magnetic field. NRM, χ, and χ_ARM generally indicate the concentration of magnetic minerals in samples. Upon completion of above measurements, wet cube samples were then oven-dried at 40°C and weighed to calculate dry-based mass-specific magnetic parameters (Table T1).

Splits of the 1 cm³ plug samples (powdered) were used for magnetic hysteresis and thermomagnetic analyses. Two plug samples were collected per core (Table T2). Powder samples of 0.3–1 mg were prepared for magnetic hysteresis analysis. Each powder sample was wrapped with aluminum foil ~5 mm long. Coercivity (Hc), remanent coercivity (Hcr), saturation remanent magnetization (Mr), saturation magnetization (Ms), and high-field magnetic susceptibility (HFMS) were obtained with an alternating gradient-force magnetometer (Princeton Measurement Corporation, MicroMag. Model 2900-02) at Kyoto University. Ms and Mr indicate the concentration of magnetic minerals in samples. Hcr and Hc are reflected in magnetic grain size in the samples. Using the definition by Day et al. (1977), Hcr/Hc and Mr/Ms values are calculated and presented in Table T2. HFMS value was determined from the linear trend of the induced magnetization between 0.7 and 1.0 T and is influenced by paramagnetic, diamagnetic, and antiferromagnetic signals in samples. In order to diagnose for magnetic minerals, high- and low-temperature magnetometry were performed. To measure low-temperature magnetometry, ~20 mg of powder sample was wrapped with plastic film. Isothermal remanent magnetization (IRM) was imparted at 5 K in a DC field of 1.0 T, and changes in the IRM were measured after each heating step of 1 K up to 300 K using a Quantum Design MPMS XL5 at Okayama University of Science (samples from Sites U1302 and U1303) and the Center for Advanced Marine Core Research in Kochi University (samples from Sites U1304 and U1308). To measure high-temperature magnetometry, a sediment sample from Site U1308 was heated from room temperature to 600°C and cooled in air at a rate of ~8°C/min in an applied field of 0.4 T using a thermomagnetic balance at Doshisha University.

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