The Gulf Stream System is one of the most important components of the North Atlantic Circulation. Reciprocal acoustic transmissions have been analyzed to determine the structure and variability of temperature, current velocity, and relative vorticity in a region just south of the Gulf Stream. Observational evidence is presented that the Gulf Stream is the source of the energetic eddy variability found in the Atlantic interior. Through highly nonlinear processes, eddy activity (energy) radiates away from the Stream southward via Rossby wave packets.