Distribution of Alexandrium excavatum-type cysts in recent and postglacialsediments of eastern Canadian margins.

Palynological analyses were performed in surface sediment samples from the North Atlantic and adjacent basins in order to document the distribution of organic-walled cysts of the toxic taxon belonging to Alexandrium excavatum . The major occurrence of the cysts along the south Scandinavian and southe astern Canadian margins reveals affinities of this taxon for neritic enviro nments with cool-temperate (15-17 degrees C in August) and relatively low s alinity (similar to 32 parts per thousand) conditions in surface waters. In the Gulf of St. Lawrence area, cyst abundances increase from the Estuary t o the outlet of the Gulf (Cabot Strait). The analyses of postglacial sedime ntary sequences from this area show a maximum abundance of Alexandrium exca vatum-type around 9000 BP, which corresponds to the beginning of the presen t interglacial. This acme is marked by particularly high concentrations (up to 10(4) cyst.cm(-3)) at the outlet of the Gulf of St. Lawrence (Cabot Str ait area). Both the recent and postglacial distribution of the cysts of Ale xandrium excavatum-type along the eastern Canadian margins suggest a region al seeding in the Gulf of St. Lawrence from the adjacent North Atlantic ner itic zones.