Plankton distributions in relation to physical oceanographic features on the southern Malin Shelf, August 1996

The distribution of plankton in relation to physical oceanographic features on the southern Malin Shelf and in the North Channel of the Irish Sea was investigated during August 1996. The near surface 13.5 degrees C isotherm and 35.20 isohaline marked the location of the Islay and Irish coastal fronts, respectively. An additional salinity front was observed to the south-east of Islay. A mergence of the Irish coastal front and the salinity component of the Islay front suggested that, at certain times, a frontal boundary separating coastal and oceanic water may extend from south-west Ireland north along the western Scottish Shelf. The presence of highly saline (35.35) water on the outer shelf indicated the intrusion of Atlantic water.The frontal boundaries influenced the distribution of plankton on the southern Malin Shelf and in the North Channel. The outer shelf region was characterized by the presence of Chaetoceros atlanticus, Gonyaulax polygramma, Oxytoxum scolopax, Doliolum gegenbauri, Sagitta tasmanica, and S. maxima. Halosphaera minor and Limacina retroversa were distributed between the shelf edge and the Irish coastal and Islay fronts. Gyrodinium aureolum dominated the phytoplankton of the Islay front but in contrast, Ceratium longipes was restricted to the east of the Islay Front. The distinct spatial separation of species suggested that there was no exchange of southern Malin Shelf and North Channel water at the time of the study.