As part of the global ocean circulation, warm water is transported from the equator to the poles. Cooling and mixing with fresher water at high latitudes leads to the formation of heavy dense water masses that sink down into the deep ocean. Such water -mass transformation occurs in the Nordic Seas and is a very important part of the global ocean circulation.
In recent decades, the Nordic Seas have shown a trend of increasing temperature while the sea-ice cover has retreated from the western parts. This work focuses on the causes and consequences of the changes in water-mass transformation in the Nordic Seas with a special focus on the Greenland Sea where the changes are most drastic.
Over the past 70 years, the Greenland Sea has become both warmer and more saline while the sea -ice cover has retreated. Since the 1980s, thermobaric convection has not been observed. This is a very effective type of convection that only occurs under very cold conditions. This also meant the end of bottom-reaching convection in the Greenland Sea as well as the cessation of the formation of ‘Greenland Sea Deep Water’. The changes in salinity and temperature led to an overall transition towards the formation less dense water during winter.
While the ‘Greenland Sea Deep Water’ was too dense to flow across the Greenland-Scotland Ridge, the new less dense water mass that today forms instead, contributes directly to the global ocean circulation. The changes in the hydrographic properties thus led to a redistribution of the water flowing into the depths of the North Atlantic, which is the water from the Nordic Seas that contributes to the global ocean circulation.