Methods
Onboard magnetic susceptibility (MS) measurements were made on all piston core samples using a Bartington Instruments MS2C susceptibility bridge connected to a laptop PC. After the cores were cut into 1 m sections and split, the archive half of each section was passed through the MS bridge in 2 cm intervals. The volume of each measurement was assumed to be a semi-sphere with a diameter of 8 cm (the diameter of the core). Volume deficiencies that resulted from physical gaps in the core, as well as measurements made near the ends of core sections, resulted in low MS values, which were deleted from the datasets. As data were obtained section by section, section data were later compiled and plotted for each piston core, as shown in the appendix. MS values are given in SI units.

Observations
The onboard susceptibility measurements, while not as precise as discrete measurements, provided immediate useful information to shipboard scientists. In most cases, high MS values correspond very well to the presence of visible black, volcanic sand in the piston cores. Presumably this is due to the presence of magnetite in the sands, which are interpreted to be turbidite deposits from landslide events off the Hawaiian islands. Because of the correlation with turbidites, MS profiles from geographically neighboring piston cores correlate very well with one another.

Visually identified volcanic sand units have MS values ranging from 220 to 400. Pelagic sediment, the dominant lithology of the cores, typicall y ranges from 40-100. In two cores, PC10 and PC-11, fossiliferous ooze was identified. This wholly biogenic material has very low MS, with values of 2-8.

The following list outlines some of the most useful and interesting aspects of the onboard MS measurements:Identification of coring inflow. Portions of several cores, especially at the bases, were observed to have structures indicative of inflow during the coring process. For these portions of the cores, the MS values were abnormally constant, suggesting that efficient mixing of sedimentary layers occurred during inflow, and providing a confirmation of visual observations.

Identification of volcanogenic material. A comparison of visual observations and MS measurements for a given piston core reveals a strong correlation between black sand layers and high MS, as would be expected. However, several cores show intervals of high MS that do not correlate with visible black sand layers. These horizons may contain volcanic material, but not in high enough abundance to be visible. We will be able to confirm this by closer examination of the horizons at a later time.

As recognized by Naka et al. (2001) pelagic sediment between sand layers can contain volcanic glass fragments. The range of MS for the sediments between sand layers likely reflects this. Some of the high MS horizons in the cores have a peak at the base and gradual decrease in MS up section. This may reflect initial pulses of volcanic sand followed by reworking and mixing with pelagic sediments, and thus could provide information on turbidite emplacement processes.

Determination of glass versus lithic content of black sand layers. Visible black sand layers have MS values typically between 230 and 400, with one layer having MS of 552 (PC-13, 130 cm bsf).Likely this wide array of MS values reflects varying proportions of glass versus lithic contents in the sands. This seems to be corroborated by preliminary observations of smear slides, but more detailed work is needed to quantify the relationship between MS and lithic/glass ratios.

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Figure pc3. Magnetic susceptibility profile of core PC7 through 15