The underwater environment of the Antarctic dry valley lakes is an exception to the usual paradigm concerning the light regime of planktonic microalgae. In most ecosystems, phytoplankton experience light variability on a range of time scales related to the vertical mixing rate. In the permanently ice-covered dry valley lakes, it is hypothesized that a hydraulically stable water column results in extreme constancy of light intensity and spectral quality. This project will characterize the photophysiology of distinct phytoplankton populations in Lake Fryxell with respect to the non-fluctuating physical regimes. The research will examine the stability of the physical environment, habitat preferences for distinct vertically stratified populations, time kinetics of photoadaptation, diel rhythmicy of photosynthesis and the physiological mechanism responsible for observed photosynthesis versus irradiance patterns. Since these populations are relatively stable in space, they will provide a model system for studying photoadaptation as it occurs over the growing season.
