Appendix: Magnetic Experiments

During Leg 189, magnetic experiments were continued in an attempt to understand and mitigate the troublesome magnetic overprints encountered in the paleomagnetism of recovered Ocean Drilling Program (ODP) sediment cores. Although these overprints do not interfere with magnetostratigraphy, except at low-latitude sites, they degrade some records sufficiently that the potentially invaluable reversal and secular variation records in the cores are not usable for high-resolution work. A nonmagnetic advanced hydraulic piston core (APC) barrel assembly was run on alternate APC cores throughout the leg, and the results from cores obtained with it were compared with those cored with the standard assembly. Further comparisons were made between long-core measurements from the whole sections (i.e., before splitting) and the archive halves early during the leg. For the majority of the sites, the whole sections were used for the long-core measurements. The prevalence of disturbance at Site 1169 resulted in analysis of cores that had suffered extreme deformation. Measurement of these weak carbonate cores also makes apparent magnetic noise from sources such as core liners, which are not seen in the results from more strongly magnetized cores. Finally, we have investigated the possibility that for weak samples, such as carbonates, an instrumental malfunction can give an expression to the “0°” declination anomaly. Preliminary results of these various investigations are presented here and will be included in a comprehensive paper to be published postcruise.