Picophytoplankton Photoacclimation and Mixing in the Surface Oceans

摘要

Fluctuations in light intensity due to vertical mixing in the open ocean surfacelayer will affect phytoplankton physiology. A combination of laboratory and field experimental work, field observations, and theoretical models were used to quantify the relationship between vertical mixing and photoacclimation in determining the time and space evolution of single cell optical properties for the photosynthetic picoplankton, Prochlorococcus spp. Diel time-series observations from the Sargasso Sea reveal patterns in single-cell fluorescence distributions within Prochlorococcus spp. populations which appear to correspond to decreasing mixing rates and photoacclimation during the day, and increased mixing at night. Reciprocal light shift experiments were used to quantify the photoacclimation kinetics for Prochlorococcus spp. fluorescence. A laboratory continuous culture system was developed which could simulate the effects of mixing across a light gradient at the level of the individual cell. This system was operated at four different simulated diffusivities.