Robert J. Olson and Heidi Sosik; Woods Hole Oceanographic Institution

"Regulation of primary production in the Southern Ocean: Phytoplankton photosynthesis characteristics from individual cell measurements"

Our objective is to determine the mechanisms regulating phytoplankton growth and productivity in the Southern Ocean in the summer, by examining the photosynthetic characteristics of phytoplankton in natural populations under a range of environmental conditions. We will estimate, from chlorophyll fluorescence induction measurements of individual cells, the photochemical efficiency and absorption cross section of photosystem 2, as well as relative pigment content per cell for different groups of phytoplankton. These measurements should allow us to distinguish between growth limitation by low light, micronutrient (i.e., iron) supply, and grazing pressure.