ORIGIN AND ACCUMULATION OF ORGANIC MATTER IN THE CANARY BASIN – IMPLICATIONS FROM ORGANIC GEOCHEMISTRY OF LIPIDS IN MARINE SEDIMENTS

The continental margin off the coast of Northwest Africa constitutes an area of upwelling/marine productivity with special characteristics: (a) a wide shelf area (b) a wide zone of upwelling (c) proximity to a large dust source – the Saharan desert. The Canary Islands being a divide the slope into a northern area of primary productivity and accumulation of organic matter and a southern area. Accumulation of marine organic matter (OM) is augmented by input of Saharan dust containing adsorbed terrestrial OM. The n-alkane distributions showed a pronounced maximum around C₂₉ and C₃₁ with a strong odd over even predominance, and a second much less pronounced maximum around C₁₅ and C₁₇, indicative of a recent marine origin for the organic matter. Fatty acids show similar distributions of carbon atom species with a higher content and a substantially higher C₁₆/C₂₆ ratio in nearer surface sediments of the slope samples and which rapidly decreases down into the sediment. PAH indicate very low values, representative of normal pre-industrial concentrations compared to other than marine environments. No other human pollution effects could be detected. Perylene data suggests diagenetic processes in progress down the sediment core Data from the slope sediments is comparable to the most recent organic-rich turbidite ‘a’ on the Madeira Abyssal Plain. Turbidite ‘a’ was emplaced about 1000 years ago, incorporating slope deposited material over a 200 000 year time period, from the northern source area.