Professor Brzezinski's research focuses on a dominant group of marine phytoplankton, the diatoms. Diatoms are unique among the phytoplankton in that they require silicon to grow which they deposit in their ornately patterned cell walls. That requirement for Si is obligatory and without a source of dissolved silicon diatoms cease to grow. A major focus of Brzezinski's research is to assess the role of silicon as a limiting resource for diatom growth in the sea. His studies of silicon limitation of diatoms in Gulf Stream warm-core rings, in the Sargasso Sea and in the coastal waters off Southern California and in the Southern Ocean have established silicic acid availability as a strong determinant of the level of diatom activity in these systems.