The summer distribution of net plankton dinoflagellates and their relation to water movements in the NE Atlantic Ocean, west of Ireland

A grid of 28 stations on the continental shelf and slope region west of Ireland, which included the Porcupine Bank and the Porcupine Sea Bight, was sampled for net phytoplankton in the summer (June and July) of 1995. Armoured dinoflagellates were recorded on both a relative abundance and presence/absence basis. Results showed good agreement with the physical circulation of the region, based on an analysis of seasonal current meter data from the upper 500 m of the water column. The distributions of some dinoflagellate species, known to have either a mainly oceanic or warm temperate distribution, indicated the existence of two separate slope currents in the region, one along the Irish Shelf with a source in the Bay of Biscay, and the other along the western slope of the Porcupine Bank fed by the North Atlantic Current waters. The data presented here support the idea that, in summer at least, the slope current west of Ireland is not entirely coherent in the upper layers of the water column.