The Norwegian and the Greenland Seas (NGS) are located in the transitional zone between the North Atlantic and the Arctic Ocean interior. Stratification and circulation of water masses in the NGS strongly depend on advection of the Atlantic Water (AW) and the Polar Water (PW). Properties of water masses, driven by these flows, are affected by the interaction with the atmosphere amplified northward. Water properties in the upper layer significantly influence weather and climate condition in Europe. Intermediate and deep waters, formed within the NGS, contribute to the deep-water overflows towards the adjacent abyssal areas of the North Atlantic and the Arctic Oceans.

The classification algorithm, based on cluster analysis, was developed as the appropriate means to discriminate distinct water masses within the areas, which are characterized by strong diversity of water types. This algorithm was successfully applied for the NGS. Oceanographic data (more than 130000 vertical profiles), covering the period 1900-1998, were analyzed together with meteorological records. Significant relationships between salinity stratification, winter convection intensity and atmospheric circulation have been revealed out of regional features of the oceanographic parameters time series.

Changes in advection properties and interaction intensity with atmosphere along AW pathway in the NGS jointly control the rate of the water mass transformation in the NGS. Severe weather conditions in 1960-1965 in combination with the increased inflow of high salinity AW led to density elevation in the upper layer. This was followed by strong intensification of convection in the ice-free regions of the NGS. GSA'70th had decreased salinity in the upper layer of the NGS. Hence, the vertical exchange has been switched to a new mode, which is characterized by reduced deep-water ventilation and rapid temperature increase in the deep-water. If the deep-water outflow to the North Atlantic and compensatory inflow of the AW into the NGS will be balanced at this reduced equilibrium, an increase of air temperature in high latitudes, which is attributed to the global warming, may be lowered or even ceased. There are some observation-based evidences that water motion inside the NGS becomes more cyclonic owing to prevailing western winds encouraging the PW re-circulation inside the basin. Within this scenario one might expect further decline of salinity in the upper layer of convective areas, leading to subsequent reduction of vertical exchange, controlling the thermohaline circulation.