METHODS

The cores were sampled approximately every 1.5 m (one sample per section). Selected intervals, where there was obvious lithologic cyclicity, were sampled more closely (every 0.2 to 0.4 m). Sample size was 10 cm³.

Sample preparation 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). For textural analysis, each dried sample of ~5 g was wet sieved at 63 µm (4 ) to measure sand percentage and the sand fraction weighed and retained. Fine-fraction size distribution down to 0.5 µm (11 ) was measured on a Sedigraph 5100 particle size analyzer at Royal Holloway and Bedford New College, University of London. The chosen Sedigraph output was the weight percentage within each 0.25- interval from 4 to 11 (63-0.5 µm). 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 (Sk_G) (Folk, 1974). Modal size was measured to the nearest 0.1 from each size-frequency histogram.

The data for each site are plotted against age using the sedimentation rate curves based mainly on magnetic reversal data of Shipboard Scientific Party (1999a, 1999b, 1999c).