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Samples and methods

Cube samples were taken aboard the R/V JOIDES Resolution from cores from Holes U1378B and U1379C. The cube samples used in this study were subjected to alternating field (AF) demagnetization either on ship or on shore. From each cube, ~0.5 g of sediment was sampled. Those samples were dried and gently powdered and then measured for magnetic hysteresis and thermomagnetic curves.

Hysteresis measurements were performed using a vibrating sample magnetometer (VSM, Princeton Measurements Inc.). Powder samples of ~0.1 g placed in gelatin capsules were measured. Major hysteresis loops were measured using a maximum field of 0.5 T, and I determined saturation magnetization (Ms), saturation remanence (Mrs), and coercivity (Hc) after correction for paramagnetic contribution. Coercivity of remanence (Hcr) was determined from backfield demagnetization of saturation magnetization. For selected samples, first-order reversal curves (FORCs) (Pike et al., 1999) were also measured. FORC data were analyzed using FORCinel software (Harrison and Feinberg, 2008).

Thermomagnetic analyses were conducted on initial magnetic susceptibility measurements using a Kappabridge KLY 4 (Agico). The temperature dependence of initial susceptibility, χ (T), was measured upon heating from –192°C to 15°C. Then the χ (T) curves were measured upon cycling from room temperature to 700°C in air.