Blooms of the coccolithophore Emiliania huxleyi with respect to hydrography in the Gulf of Maine

Abstract

We present results of oceanographic surveys of visually turbid blooms of the coccolithophore Emiliania huxleyi in the Gulf of Maine during the summers of 1988, 1989 and 1990. In each year, hydrographic stations within the blooms could be distinguished from non-bloom stations on a temperature-salinity diagram. In 1988 and 1989 the blooms were confined to the surface waters of the central western Gulf of Maine; T-S analyses showed they occurred in higher salinity surface waters at stations characterized by a well-defined upper mixed layer overriding a sharp pycnocline. Nutrients (not measured in 1988) were near depletion in the surface waters of both bloom and non-bloom stations in 1989, with surface phosphate being lower in the bloom waters (0.02–0.16 μM in the top 15 m) than in non-bloom waters (0.21–0.49 μM). Phosphate was not as low in the surface waters of the 1990 bloom. The bloom that year was much smaller in areal extent than in 1988 or 1989, and was limited to the northern part of the Great South Channel and western Georges Bank area of the Gulf of Maine. T-S analyses indicated significant mixing of different water masses in the area of the bloom in 1990, with the bloom being confined to those stations having less dense surface waters, of lower salinity, than the non-bloom stations. There also was evidence of a subsurface salinity minimum beneath the bloom waters in 1990. Blooms of E. huxleyi with surface expressions of visually turbid waters do not occur every year in the Gulf of Maine, and we discuss possible causative factors, specifically as related to the age or maturity of surface waters and macro- and micro-nutrient levels, that could facilitate bloom formation and which could vary between years.