Coastal upwelling in the Canary Island region: spatial variability reflected by the surface sediment diatom record

Modern diatom and C-org distribution patterns were investigated in 39 surfa ce sediment samples of the Canary region in order to quantitatively determi ne the influence of coastal upwelling and Saharan dust on the flux of these sedimentary components. High diatom abundance in surface sediments (>2 x 10(6) valves g(-1) dry sed iment) as well as the dominance of the assemblages by spores of Chaetoceros , which is a genus related to upwelling conditions, reflect the stronger co astal upwelling conditions occurring at Cape Ghir off the NW African coast. Further offshore, total diatom abundance decreases one order of magnitude (+/- 1 x 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. T his association suggest that offshore diatom concentrations may be generate d by dust input from desert regions. Even though the sediments are expected to preserve only a mixed and average d oceanographic signal, characteristic biogeographic patterns of a phytopla nkton community occurring across a gradient of turbulence and nutrient avai lability, are recorded in surface sediments off Cape Ghir. This is seen in the subsequent maximum abundances of the genera Thalassiosira, Chaetoceros and Rhizosolenia. (C) 2001 Elsevier Science B.V. All rights reserved.