Influence of the Shelf-Break Front Off Nova Scotia on Phytoplankton Standing Stock in Winter

Abstract

Observations made on the shelf-break front off Nova Scotia during winter on 2 successive yr show the concentration of chlorophyll a in the euphotic zone to be correlated to the inclination of the subsurface front. The steepness of the front influences the depth to which phytoplankton are mixed which in turn controls the average amount of illumination received by a given cell. The two winter observations showed the subsurface front at each of two extremes: vertical with little phytoplankton biomass and almost horizontal with significant quantities of chlorophyll. Calculations were made as to the amount of production enchancement that could result from shallowing of the mixed layer by decreased frontal inclination. They show that during the winter under ideal conditions as few as 35 d of intermittent growth increase annual production in the frontal region by 25%. Key words: front, winter production, phytoplankton, shelf-break, chlorophyll a, frontal oscillations, growth enhancement, stability, stratification