MATERIALS AND METHODS

Remanent magnetization after alternating field (AF) demagnetization up to 20 mT of all archive-half core sections from Site 1081 was measured at 5-cm intervals aboard ship using a 2G Enterprises pass-through cryogenic magnetometer (Wefer, Berger, and Richter, et al., 1998); selected working-half core sections were also measured aboard ship (Sections 175-1081C-9H-5, 10H-3, and 11H-3) (Shipboard Scientific Party, 1998).

A total of 245 discrete samples, taken aboard ship from working-half core sections at one 7-cm3 cube per section for Hole 1081A, were measured at the Geological Survey of Japan. An additional 101 discrete samples (10-cm3 cubes) and U-channels, taken postcruise, were measured at the Hawaii Institute of Geophysics and Planetology (HIGP).

Equipment used at the HIGP paleomagnetics laboratory included a an in-line degaussing system capable of peak alternating current (AC) fields up to 120 mT (accuracy = 1%), an in-line anhysteretic remanence magnetizer, and a 2G Enterprises Model 760R cryogenic magnetometer housed in a shielded room and equipped with an automated sample handler system, which accommodates as many as eight discrete samples per tray or U-channels as long as 150 cm. Other equipment used included an ASC Model IM-10 impulse magnetizer for imparting isothermal remanent magnetization (IRM) to discrete samples and a Kappabridge KLY-2 and Minikappa KLF-3 for discrete sample susceptibility measurements, including temperature variation.

For discrete samples, intensity of natural remanent magnetization (NRM) and volume susceptibility were measured prior to AF demagnetization. After AF demagnetization, the acquisition behavior of anhysteretic remanent magnetization (ARM) was studied for 101 samples. The AF was progressively increased from 0 to 100 mT in a direct current (DC) bias field of 0.10 mT. Acquired remanence was measured between steps. The ARM was then AF demagnetized so the demagnetization behavior could be compared with that of NRM and IRM.

The acquisition behavior of IRM was studied for 15 samples. The DC field was progressively increased from 0 to 1.2 T; the IRM was measured between steps. Saturation IRM (SIRM) was estimated from the remanent magnetization at 1.2 T. A reversed-field IRM at 300 mT was imparted after growth and measurement of IRM, after which SIRM was again imparted and AF demagnetized. Hysteresis data were measured at room temperature using a MicroMag Model 2900 alternating gradient magnetometer.

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