Modified CO2 cycle for long endurance unmanned underwater vehicles and resultant chirp acoustic capability

A carbon dioxide cycle power generation system includes storage collectively storing portions of carbon dioxide liquid and gas and a transfer connection selectively directing flow of the carbon dioxide through a turbine. The system cycles between different seawater depths in order to employ at least one of seawater pressure and seawater temperature in creating the carbon dioxide flow. Inlet/outlet control valves on variable volume tanks, positioned below movable pistons within the respective tank, selectively allow seawater into or out of a lower portion of the respective tank below the piston to pressurize the carbon dioxide therein relative to the carbon dioxide within the other tank when at depth rather than near the surface. Inhibited versus uninhibited heat transfer between storage portions and the seawater allows different seawater temperatures at depth and near the surface to create the carbon dioxide flow. Acoustic communications may be driven concurrent with the turbine.