Abstract
Modern diatom and C org distribution patterns were investigated in 39 surface sediment samples of the Canary region in order to quantitatively determine the influence of coastal upwelling and Saharan dust on the flux of these sedimentary components. High diatom abundance in surface sediments (>2×10 6 valves g −1 dry sediment) as well as the dominance of the assemblages by spores of Chaetoceros, which is a genus related to upwelling conditions, reflect the stronger coastal upwelling conditions occurring at Cape Ghir off the NW African coast. Further offshore, total diatom abundance decreases one order of magnitude (±1×10 5 valves g −1 dry sediment) and the assemblages are dominated by oceanic species of the genus Nitzschia and fresh water diatoms, mainly the genera Aulacoseira, which is known to be a component of Saharan dust. This association suggest that offshore diatom concentrations may be generated by dust input from desert regions. Even though the sediments are expected to preserve only a mixed and averaged oceanographic signal, characteristic biogeographic patterns of a phytoplankton community occurring across a gradient of turbulence and nutrient availability, are recorded in surface sediments off Cape Ghir. This is seen in the subsequent maximum abundances of the genera Thalassiosira, Chaetoceros and Rhizosolenia.
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