Organic geochemistry of lipids in marine sediments in the Canary Basin: Implications for origin and accumulation of organic matter

Abstract

Abstract The Canary basin consists of the continental margin off the coast of Northwest Africa, the deep basin, the Madeira Abyssal Plain (MAP) and the volcanic Canary Islands. The continental margin has an area of upwelling marine productivity with special characteristics: (a) a wide shelf area, (b) a wide irregular zone of upwelling, and (c) proximity to a large dust source—the Saharan desert. The Canary Islands divide the continental slope into a northern area and a southern area of primary productivity and accumulation of organic matter (OM). Accumulation of marine OM in the northern area is augmented by input of Saharan dust containing adsorbed terrigenous OM. n -Alkane distributions show a pronounced maximum around C 29 and C 31 with a strong odd-to-even predominance typical of terrigenous OM. There are less pronounced maxima near C 15 -C 17 , indicating a recent marine origin for the OM. Fatty acids show carbon number distributions similar to the n -alkanes, with a higher content and substantially higher C 16 /C 26 ratios in near-surface sediments of the slope samples, which decrease with depth in the sediment. The above data from the slope sediments can be compared to the most recent organic turbidite “a” on the MAP. Turbidite “a” was emplaced about 1000 years ago, incorporating slope derived material representing a 200,000-year time period. TOC and biomarker signatures of sediments on the slope are comparable to turbidite “a”. Biomarker analyses of deeper sediments on the MAP show similar data continuing back to early Miocene. Comparison of recent seafloor surface biomarkers with deeper samples indicates a varying contribution of terrigenous OM and a strong degradation of marine OM components in favor of leaving the long-chained compounds that increase a terrigenous signature of the sediments. The marine component is higher than analysis of deeper biomarkers tends to indicate. Polyaromatic hydrocarbons (PAH) are low in concentration, and no human pollution effects were detected. Perylene data suggest active diagenesis down the sediment core.