Data for discrete samples from Hole 1081C are summarized in Table T1. NRM intensities range from 2.68 × 10-5 to 7.67 × 10-4 A/m (mean = 1.51 × 10-4 A/m), whereas remanent intensities after AF demagnetization at 20 mT vary from 4.66 × 10-6 to 1.95 × 10-4 A/m (mean = 4.13 × 10-5 A/m). ARM intensities acquired during AF demagnetization at 100 mT range from 1.18 × 10-3 to 8.45 × 10-3 A/m (mean = 2.91 × 10-3 A/m). SIRM intensities range from 2.46 × 10-2 to 6.71 × 10-2 A/m (mean = 4.51 × 10-2 A/m). Backfield IRMs induced at -0.3 T range from 2.26 × 10-2 to 6.03 × 10-2 A/m (mean = 4.10 × 10-2 A/m). Susceptibility values for discrete samples measured postcruise range from 1 × 10-6 to 39 × 10-6 SI (mean = 19 × 10-6 SI). Complete data from all measured discrete samples and U-channels are available from the ODP Data Librarian; long-core data measured aboard ship are available from the ODP online database.
Figure F2 illustrates ARM acquisition curves and the demagnetization behavior of NRM, ARM, and SIRM for selected discrete samples from Hole 1081C. The median destructive field (MDF) for NRM data varies between ~5 and 40 mT. During ARM acquisition, normalized intensity values (J/Jo) gradually increase over a broad range of peak AF fields; saturation of ARM is not achieved until ~80 mT for all measured samples. Demagnetization of ARM shows MDF values between 10 and 20 mT downhole to Sample 175-1081C-8H-3, 86-88 cm, with the first and shallowest sample (175-1081C-1H-3, 98-100 cm) showing an MDF value near 25 mT. The remaining (and progressively deeper) samples show generally higher MDF values between 25 and 30 mT. The last sample shows an MDF value of 20 mT. MDF values for demagnetization of SIRM are consistently between ~30 and 40 mT.
IRM acquisition curves are shown in Figure F3. The similarity in the shapes of all 15 curves is striking; all show sharply increasing intensity values below 0.1 T with near saturation of IRM achieved by 0.3 T. S ratios (Bloemendal et al., 1992) are uniformly very high (Fig. F4) (mean = 0.96; maximum = 0.96; minimum = 0.92; standard deviation = 0.01), which indicates a higher proportion of low-coercivity magnetic minerals relative to high-coercivity minerals.
Figure F5 illustrates the temperature dependence of susceptibility for selected discrete samples. Throughout the heating and cooling phases of the experiment, susceptibility values remain extremely low (10-5-10-6 SI). Susceptibility values were negative throughout the heating phase of the experiment for all measured samples, which is characteristic for diamagnetic minerals. For two samples (175-1081C-3H-2, 100-102 cm, and 175-1081C-10H-3, 74-76 cm), the susceptibility increased significantly during heating between ~225°-300°C and 250°-300°C, respectively, indicating the formation of a new magnetic mineral. Above these temperatures, susceptibility values drop and thereafter remain low up to the maximum temperature. A gradual increase occurs up to ~475°C during heating for Sample 175-1081C-15H-3, 52-54 cm, but no dramatic increase like that observed in the previous samples is apparent.
During cooling of all three samples, susceptibility values increased sharply beginning at ~575°, 525°, and 580°C, respectively, and continued to increase to positive values before peaking near 425°, 225°, and 350°C, respectively (Fig. F5). Positive susceptibility values persist for the remainder of the cooling cycle, decreasing gradually below ~200°C for Sample 175-1081C-3H-2, 100-102 cm, and shortly after peaking for the remaining two samples.
Hysteresis data are dominated by paramagnetic behavior (Fig. F6) with no evidence for a ferrimagnetic component after correction for paramagnetic behavior.
NRM intensity data from Holes 1081A and 1081C show inconsistencies between data collected on the ship and data collected on shore after the cruise (Fig. F7A). Discrete samples from Hole 1081A show intensity values that are generally on the same order of magnitude as shipboard data, with notable exceptions. Between ~120 and 170 mbsf, intensity values measured up to two orders of magnitude higher than shipboard data collected from long cores. The intensity values of discrete samples above ~50 mbsf are lower than, but on the same order of magnitude as, shipboard data. Intensity values of discrete samples below ~320 mbsf are higher than, but on the same order of magnitude as, shipboard data.
Discrete samples from Hole 1081C show intensity values up to two orders of magnitude lower than shipboard data collected from long cores (Fig. F7A). The marked intensity loss is probably due to a greater time lag between measurement of long cores and discrete samples at this hole than at Hole 1081A.
U-channel intensity data from two sections are consistent with shipboard data from long cores above ~54.9 mbsf but diverge from shipboard data below this depth (Fig. F7B).
Susceptibility data for discrete samples at Hole 1081C are up to one order of magnitude lower than shipboard whole-core susceptibility measurements (Fig. F8).