Instabilities of the jets associated with the Antarctic Polar Front and the Southern Polar Front generate cyclonic eddies which are trapped within the Antarctic Circumpolar Current. These eddies can be long-lived and exist for many months. In their core these eddies contain distinct masses of the cold Winter Water which show a wide variety of thermohaline characteristics determined by the water subducted when the eddies form. Once trapped within the eddy the Winter Water gradually warms by diffusive processes.