Light-Dependent Oxygen Cycling in Marine Systems Measured by 18o Tracer Techniques

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Dr. Kana will address the general question of "light respiration" in marine waters. Considerable direct and indirect evidence indicates that light can significantly affect oxygen consumption: in some cases elevating the rate up to 10 times the rate of dark respiration. What this stimulation of oxygen consumption means in terms of organic cycling is very poorly understood due to the historical difficulty in measuring the fluxes and the simultaneous occurance of at least 5 distinguishable oxygen uptake processes. Recent development in Dr. Kana's laboratory of two isotope (180) methods capable of measuring oxygen cycling in the light provide the basis for tackling this problem. The research coordinates field measurements of light-dependent oxygen uptake and evolution in an estuarine habitat with controlled laboratory studies of oxygen cycling in phytoplankton species isolated from the study site. The major variables of interest are phytoplankton composition, defined by seasonal cycles, and light intensity. Field experiments center around characterizing the effects of seasonal and event scale phenomena on oxygen cycling, especially as mediated by the phytoplankton. Laboratory experiments center around the identification of the physiological processes responsible for light-dependent oxygen uptake. In a related study, Dr. Kana will continue collaboration with Drs. Carpenter and Capone in the study of oxygen cycling in Trichodesmium.