10°) but have the same pattern. From this agreement in direction and intensity, we conclude that the core pieces can be regarded as homogeneously magnetized.
In addition to routine half-core measurements, whole-core NRM data were obtained from two sections in Core 209-1274A-6R that had the highest recovery (Sections 6R-2 and 6R-3). The aim of these measurements was to test the influence of the core geometry on both the intensity and directional data obtained from the 2G Enterprises magnetometer (Fig. AF1). The measurement of pieces >50 cm permits easier comparison between the whole-core and archive-half data without the interference of edge effects at piece ends.
To first test homogeneity of the remanence in the core, pieces from Section 209-1274A-6R-3 were measured in two different positions, first with the core +x parallel to the SQUID +x-axis, and then with the core +x parallel to the SQUID +y-axis (Fig. AF1A). The inclination and intensity records from these two runs are essentially identical. After accounting for the ~90° rotation described above, the declinations from these two measurements differ by a consistent offset (10°) but have the same pattern. From this agreement in direction and intensity, we conclude that the core pieces can be regarded as homogeneously magnetized.
Having established the homogeneity of the magnetization, we next compared the results obtained for the whole-core and archive-half measurements (Fig. AF1B). The two sets of measurements show differences both in intensity and direction of the remanence. Inclination and intensity appear to be negatively correlated; higher intensities are associated with lower inclinations and vice versa. In addition, the sense of the discrepancy between the two measurements is apparently dependent on the length of piece from which the readings were taken. Archive-half data from shorter pieces (Section 209-1274A-6R-2 [Pieces 2, 3]) yielded higher intensity and lower inclination than whole-core measurements. In contrast, archive-half measurements at the center of a long piece (Section 209-1274A-6R-2 [Piece 1]) showed lower intensities but steeper inclinations than whole-core runs. An unexpected result was that the largest discrepancies (as much as 8° in inclination and several tens of degrees in declination) between whole-core and half-core data in long core pieces were observed in the middle region of the piece.
The fact that the fluctuations in direction correlate with remanence intensity suggests that it is a measurement artifact that affects both the whole-core and the half-core data, but is more accentuated in the latter. It may be caused by a signal from source along the z-axis inducing a signal in the x- and y- SQUID sensors, particularly from off-axis sample regions (Parker and Gee, 2002). The symmetry of the magnetometer helps to cancel some of this cross-talk for whole-core measurements, but the likely centimeter-scale variability in the intensity of the remanence will produce inevitable nonzero average cross-talk. This problem will be even more severe for archive-half measurements, because these measurements lack a mirror symmetry about the y–z plane (x = 0).