A water mass (salinity 34.9–35.03%, temperature 1.0–2.5 °C) that was originally believed to form in an area off the southern tip of Greenland, where winter cooling of saline waters was thought to cause a body of water to sink and spread south. It is now recognized that the main source is in the Norwegian Sea, from which deep water flows over the sills between Scotland, Iceland, and Greenland and cascades into the depths of the Atlantic.