Weddell Sea Deep Water influences the thermohaline circulation of the world ocean directly as a component of the deep western boundary current in the South Atlantic Ocean and indirectly by cooling and freshening Circumpolar Deep Water. Because it is filled with recently ventilated Weddell Sea Deep Water, the Scotia Sea is important to both influences. The main component of the abyssal waters renewing most of the world oceans via deep boundary currents is the Circumpolar Deep Water of the Antarctic Circumpolar Current. Weddell Sea Deep Water is recognized as the main source of cold, fresh waters to Circumpolar Deep Water, and we show that Weddell Sea Deep Water is incorporated into the Antarctic Circumpolar Current within the Scotia Sea. As a result of this ventilation, the Scotia Sea provides an effective link between the deep waters of the Weddell Sea and the rest of the world abyssal ocean. Some of the Weddell Sea Deep Water filling the Scotia Sea leaves as a westward flow via the southern Drake Passage. Weddell Sea Deep Water also enters the Georgia Basin directly from the Scotia Sea and flows beneath the Antarctic Circumpolar Current to contribute to the deep western boundary current of the Argentine Basin. In most previous studies, a deep spreading route from the Weddell Sea over the South Sandwich Trench east of the Scotia Sea had been considered the only source of Weddell Sea Deep Water for this deep western boundary current.