Phytoplankton biology of a thermal front in the Celtic Sea

Abstract

SEASONAL thermal fronts which occur in coastal waters are typified by sharp lateral gradients of temperature at the sea surface resulting from a surface outcropping of the thermocline. The frontal regions are areas of considerable physical and biological activity; in the case of the fronts in the Celtic and Irish Seas this increase in biological activity is reflected in marked increases of chlorophyll a at the sea surface¹. Considerable data on the spatial distribution of physical and chemical characteristics of the water and chlorophyll a concentrations in the vicinity of these and other fronts are now available^2–5. But, few observations have been made either on the temporal variability of these characteristics or on the more detailed distribution of phytoplankton productivity. During a survey of the Celtic Sea in September 1976 we made consecutive crossings of the frontal region in order to investigate the small-scale distributions of chlorophyll a and primary productivity and their interrelationships with selected physical and chemical variables.