The significance of subsurface chlorophyll, nitrite and ammonium maxima in relation to nitrogen for phytoplankton growth in stratified waters of the Gulf of Maine

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Abstract
Data on the distributions in summer of phytoplankton and inorganic nutrients in the Gulf of Maine and across Georges Bank are presented. The chlorophyll maximum represents a phytoplankton biomass maximum and occurs at a depth where both light and nitrate availability allow net growth of the population. The dominant species were generally flagellates and included the toxic dinoflagellate, Gonyaulax tamarensis var. excavata, at some stations. The ammonium and nitite profiles suggest that nitrification is occurring at the base of the pycnocline below the chlorophyll maximum, and this may be an important source of nitrite during the summer months. The highest levels of nitrite and ammonium were over the slopes of Georges Bank.