Plankton Dynamics and Nutrient Enrichment of the Scotian Shelf

Four seasonal cruises were conducted on a 270-km-long transect normal to the coast of Nova Scotia. Most biological variables measured along this transect show maximum values in the outer 90 km. These maxima usually occur closely associated with an oceanic front which is a consistent feature of this region. Enhanced vertical transport of nutrients is postulated to occur along this front, although the mechanism is unknown. A model proposed several years ago to explain shelf enrichment off the northeastern United States was examined and found to be consistent with the Scotian Shelf data. Sporadic advection of nutrient-rich Slope Water onto the shelf at the average rate of 0.33 cm∙s−1 would, upon entering the euphotic zone, satisfy 20% of phytoplankton nutrient requirements during the spring and summer. Recycling would account for the remaining 80%. Key words: phytoplankton, zooplankton, enrichment, Scotian Shelf, excretion, fronts, nutrients, productivity, advection, recycling