Abstract: A novel waterborne cultivator, which provides the benefits of known systems for culture of photosynthetic micro-organisms in a novel configuration, incorporating a simplified, two-phase rotary mixing and gas injection system, the two phases being liquid and gas (CO2). The mixing system provides optimum growth conditions through increased turbulent vertical mixing and increased levels of dissolved CO2 throughout the cultivator via injection of flue gas or other CO2-bearing gas stream. The system thus provides efficient capture and sequestration or reuse of CO2 while producing valuable biomass for food, feed, and fuel use. The waterborne configuration provides further benefits of passive temperature control and automatic leveling for consistent culture depth. Additional benefit is provided by an enclosed design which reduces contamination and evaporative loss by isolating the photosynthetic culture from the outside environment.