) to measure sand percentage, and the sand fraction was weighed and retained. A few strewn sand-fraction slides were made to check for the presence of the radiolarian Stylatractus universus (a marker for Stage 11) in upper Quaternary sediments.
The cores were sampled approximately every 1.5 m (one sample per section). Selected intervals, where there was obvious meter-scale lithologic cyclicity, were sampled more closely (every 0.2 to 0.4 m). For this study, cyclicity was delineated using a combination of shipboard core descriptions, core photographs, and physical properties, particularly magnetic susceptibility and color reflectance (Shipboard Scientific Party, 1999). As far as possible, sampling was confined to massive or bioturbated (hemipelagic) intervals, avoiding laminated sands, silts, and silty clays attributed to turbidite deposition (see below).
Sample preparation (sample size = 10 cm3) was carried out at the British Antarctic Survey. Biogenic silica (in the form of diatoms, radiolarians, and rare silicoflagellates) was measured by point-counting a smear slide made from each sample. This method is quick, but tends to overestimate silica compared with the true weight percentage (Pudsey, 1993; see Hillenbrand and Fütterer, Chap. 23, this volume). For textural analysis, each dried sample of ~5 g was wet-sieved at 63 µm (4 ) to measure sand percentage, and the sand fraction was weighed and retained. A few strewn sand-fraction slides were made to check for the presence of the radiolarian Stylatractus universus (a marker for Stage 11) in upper Quaternary sediments.
Fine fraction size distribution from 63 to 0.5 µm (4-11 ) was measured on a Sedigraph 5100 particle size analyzer at Royal Holloway and Bedford New College, University of London. The Sedigraph determines equivalent settling diameter; bulk sediment was measured, without removal of biogenic silica, so diatoms are treated as part of the sediment. Because of their low density and porous structure, they behave hydrodynamically like grains of smaller diameter. The chosen Sedigraph output was the weight percentage within each 0.25- interval from 4 to 11 . The very high clay content of most samples (commonly >70% finer than 8 [4 µm] and >40% finer than the measurement limit of 11 ) necessitated extrapolation of the fine end of the cumulative frequency curves to obtain values of 16 to calculate the standard grain-size parameters of sorting (
G) and skewness (SkG) (Folk, 1974). The sand fractions were visually inspected to assess the degree of sorting, and a few representative sands were dry-sieved at 1- intervals.
The data for the whole recovered section are plotted against age. The data for the shorter cycles are plotted against depth as well as age, since the linear age interpolations may not be very accurate at the meter scale. The raw data are given in a data report by Pudsey (Chap. 12, this volume).
Spectral analysis was carried out on three parts of the section that showed reasonably clear (to the human eye) cyclicity in lithology and physical properties. Power spectral routines in the package MATLAB 6.1 were used; these are based on Welch's periodogram method (Welch, 1967).
