NUTRIENT LIMITATION IN ELLIS FJORD, EASTERN ANTARCTICA

The occurrence of high chlorophyll-a concentrations (up to 11.6 mu g l (-1)) at shallow depths within Ellis Fjord, eastern Antarctica, during spring and summer, coincided with the development of a stratified wat er column. Macronutrient concentrations during periods of high chlorop hyll-a levels were very low. Phosphate concentrations decreased to 0.2 mu M, nitrate to 0.4 mu M and silicate to 3.9 mu M. High rates of nut rient depletion early in the season can be explained by strong sea-ice algal mat development. An Si:N:P uptake ratio of 25.5:13.8:1 indicate s a strong demand for silicate. Minimum silicate levels were below tho se necessary for maximum diatom growth and probably contributed to the successional shift from diatoms to phytoflagellates.