ALBERT

Description: An organic-rich, diatomaceous sediment core from the shelf off Walvis Bay has been examined for the composition and variation in some of the major organic fractions, together with analyses of the lipid and amino acid content. Many intact and partially altered planktonic pigments and lipids are present, indicating good preservation over the 1000-year period of accumulation of the sediment. The fatty acid and fatty alcohol compositions were similar to that in marine diatoms and planktonic crustaceans although the longer chain unsaturated acids and alcohols (C20-Cu) were in lower concentration and odd-numbered normal and branched-chain C15 - C17 acids were present. Some influence of bacterial activity may be indicated by the presence of odd-chain acids. The n-alkanes have distribution maxima at Cl7 at the sediment surface and C25-C17 and Cl7-19 at depth. CPI values are all low. No polyunsaturated hydrocarbons were found. Aromatic hydrocarbons were present in all core samples. A number of sterols were present at the sediment surface, with cholesterol being the most abundant. These compounds arc identical to those found in diatom and crustacean lipids with the exception of methylene cholesterol. The amino acid composition changes slightly with depth in the core, acidic acids falling and valine, arginine and aromatic acids increasing with depth. Fulvic acid levels arc high at all depths in the core, whereas humic acid levels are significantly lower. Conversion of the planktonic organic material to higher molecular weight compounds appears to be slow.