Samples for IRD analysis were taken at regularly spaced intervals throughout the 218-m sedimentary section at Site 1101. Although the fine-grained sediments at this site do not contain any visible hiatuses, the site was cored only once and therefore it is not possible to determine if there are any gaps between cores. The depth spacing between samples, average linear sedimentation rates, and resulting temporal resolution of samples are summarized in Table T1. The sedimentation rates used to calculate ages are based on shipboard paleomagnetic and biostratigraphic datums (Barker, Camerlenghi, Acton, et al., 1999). The high sedimentation rates and relatively close sample spacing result in a temporal resolution that is high enough to identify the IRD flux within both glacial and interglacial intervals. However, magnetostratigraphy does not provide data necessary to estimate variations in sediment accumulation rates between glacial and interglacial periods. Based on analogy with modern glacimarine environments and the amount of bioturbation in the sediment record, sediment appears to have accumulated much more rapidly in glacial intervals than in interglacials. Variability in sediment delivery rates is also expected during glacial periods. For example, Pudsey (2000) calculated sedimentation rates using gravity cores from drift sites and found that they ranged from 1.8 to 13.5 cm/ka during glacial stages.
Lithofacies analysis utilized shipboard core descriptions (Barker, Camerlenghi, Acton, et al., 1999) and X-radiography of U-channel samples that were collected for shore-based paleomagnetic studies.
Calculation of the IRD MAR follows the method developed by Krissek (1995) for Ocean Drilling Program (ODP) cores from the North Pacific. IRD abundance was determined from the 250-µm to 2-mm sand fraction, which was separated by wet sieving after air drying, rinsing with distilled water to remove salts, and ultrasonic vibration. The 250-µm to 2-mm fraction was dried, weighed, and the abundance of the coarse sand fraction (in weight percent) was calculated. The sand was then examined with a binocular microscope to estimate the volume of terrigenous ice-rafted sediment (in volume percent) in order to exclude biogenic components, volcanic ash, and manganese micronodules, which usually do not have an ice-rafted origin. Following Krissek (1995), the IRD MAR (in grams per square centimeter per thousand years) was calculated as
where CS% = the coarse sand abundance (multiplied as a decimal), IRD% = the IRD abundance in the coarse sand fraction (as a volume ratio), DBD = the dry bulk density of the whole sediment sample (in grams per cubic centimeter) determined from the measurement of dry bulk density on the discrete sample taken closest to the depth sampled for IRD (see "Physical Properties" in the "Explanatory Notes" chapter in Barker, Camerlenghi, Acton, et al., 1999), and LSR = the interval average linear sedimentation rate (in centimeters per thousand years).
The U-channel samples provided 2 cm × 2 cm × 150 cm strips from the center of the working half of most cores to 124 mbsf for X-radiography. A few cores were not sampled because they were disturbed during coring. Although the width is narrow, U-channel samples are of uniform thickness and are continuous through each core, making them ideal for X-radiography. Three U-channel samples were X-rayed per sheet of Kodak Industrex-M film using a portable MinXray 803 with settings of 80 kV and 20 mA. The 150-cm-long U-channel samples were exposed for 26 s in 40-cm-long overlapping sections. Each film was contact printed and spliced together to make a true-scale image of the U-channel sample. These X-radiographs were used to describe sedimentary structures and to identify lithofacies. Clasts >2 mm were counted at 1-cm spacing following the method described by Grobe (1987) to provide more continuous data than the IRD MAR method. The volume of sediment represented on each X-radiograph is 2 cm (width) × 2 cm (thickness) × 1 cm (counting interval) = 4 cm3.