Dinoflagellate cyst counts from sediment samples along a land-sea transect off Cape Blanc NW Africa (Maria S. Merian cruise MSM79)

Resumo

Dinoflagellate cyst counts obtained in surface sediment samples collected along a shelf break-offshore transect in the upwelling region off Cape Blanc (NW Africa) are presented. Data was collected in November 2018 during the cruise Maria S. Merian MSM 79. New data on organic-walled dinoflagellate cysts in sediments were compared to cyst distributions in the water column and environmental parameters to investigate the cyst dispersal and accumulation patterns in deep-marine environments, detect possible cyst resuspension and other factors affecting cyst distribution in the water column and identify possible environmental signals in the sediment cyst assemblages.Surface sediments (0-1 cm) were collected at 12 stations using a multi-core system. They were frozen at -20°C immediately after recovery. In the laboratory, sediment samples were subsampled (1 ml) and oven-dried (60 ºC for 24-48 h) to determine the dry bulk density. A known volume of each sample was processed using standard palynological techniques as described in Zonneveld et al. (2012). It included acidic digestion of carbonates (HCl 10%) and silicates (HF 40%). Cysts were concentrated by sonication and sieving through stainless steel meshes (fraction recovered <125 μm and >20 μm). Several cycles of sonication (~3 min each) and washing through the meshes with tap water were applied until the material was clean. Material was further concentrated by centrifugation (5 min at 3500 rpm) and transferred to Eppendorf tubes. The final volumes were adjusted to 0.5 to 1 ml, depending on the amount of organic content. Permanent slides were prepared by using the aliquot method to allow the determination of cyst concentrations. Slides were observed under a Zeiss Axioskop R5111 light microscope at x400 and x1000 magnifications, and all dinoflagellate cysts were identified and counted at the lowest possible taxonomic level.