Above the deeper waters of the North Atlantic that have entered from the circumpolar flow, convection in the Labrador Sea and overflow from the Mediterranean, Norwegian, and Greenland seas combine at mid-depth and circulate in the subarctic cyclonic gyre, and flow southward along the western boundary into the South Atlantic. Because of the nature of these sources the mid-depth waters of the North Atlantic are the warmest, most saline, highest in oxygen and lowest in silica of any of the mid-depth waters of the World Ocean. They have been called the North Atlantic Deep Water.In the Atlantic these characteristics have vertical extremes that separate the inflowing water from the far south into an upper and a lower layer (Reid et al., 1977). These characteristics are so strong that their patterns trace much of the large-scale circulation. Lateral extremes in these tracers extend southward along the western boundary of the Atlantic Ocean. They turn offshore near 50S and eastward with the circumpolar flow. The tracers indicate that some of the eastward flow turns northward along the western boundaries in the Indian and Pacific oceans, but the lateral extreme remains strong enough to give a clear signal all the way to the Drake Passage