Water mass components of the North Atlantic deep western boundary current

Four hydrographic sections across the North Atlantic deep western boundary current from 55°W to 70°W are analysed to distinguish the current's different water mass components. The deepest component is the Norwegian-Greenland overflow water (2–3°C) which is characterized most readily by a core of high oxygen, tritium, chlorofluorocarbons (CFCs) and low silicate anomaly. The above lying Labrador Sea Water (3–4°C) is distinguishable at this latitude only by its core of low potential vorticity. The shallowest component of the boundary current (4–5°C) is revealed by a core of high tritium, CFCs and low anomaly nut has no corresponding oxygen signal because of its proximity to the pronounced oxygen minimum layer. A careful analysis of the shallow water mass reveals that it is not dense enough to be formed in the central Labrador Sea even during warm winters. Rather, based on historical hydrography its area of formation is the southern Labrador Sea inshore of the North Atlantic current where surface layer salinities are particularly low. A simple scale analysis shows that lateral mixing with the adjacent North Atlantic current can increase the salinity of this component to the values observed in the mid-latitude data set.