Ocean conditions
The increased presence of freshwater in the upper 1000 metres of ocean first observed in the eastern subpolar North Atlantic in 2016 persisted into 2017 and expanded to include the southern Norwegian Sea. Notably, this was accompanied by above average temperatures. A gradual freshening of the upper waters (100-400 metres) of the Subtropical Gyre in the northeast Atlantic is now widespread, reaching western Iberia and the Canary Islands.
Across most of the North Atlantic region, sea surface temperature was higher than usual, except from the central subpolar North Atlantic and the Baltic Sea. In the central subpolar North Atlantic, a cold anomaly observed in the surface and upper ocean for the past four years weakened and shifted northwestward into the Irminger Sea.
Following a five-year period of increasing heat content, the temperature of the upper layer of the Norwegian Sea reached a new record high. Ocean temperatures in the western North Atlantic, however, were cooler than normal in the north, (the Labrador and Newfoundland shelves) and warmer than normal in the south, along the Northeast US Shelf.
In the Barents Sea, ice cover remained very low.
Winter atmosphere
The North Atlantic Oscillation (NAO) index is a measure of the difference in the atmospheric pressure at sea level between the Icelandic low, a centre of low pressure, and the Azores high, an area of high pressure. The index is a simple indicator of the strength of these two pressure systems and of the strength and direction of westerly winds and storm tracks across the North Atlantic that they help govern. The 2016/2017 index was positive (+1.47), meaning a stronger westerly wind system. This is the fourth consecutive winter that the index has been positive, the first such positive run since 1992-1995.
The pattern of sea level pressure (SLP) anomaly did not resemble that associated with a typical NAO positive index. Instead, the high-pressure anomaly was shifted east, centered over the North Sea, and the low-pressure anomaly over the Arctic was split to the southeast and southwest of Iceland and the Nordic seas.
Winds were more northerly over the Labrador Sea and southerly across the northeastern Atlantic and into the Nordic Seas. Winter air temperatures were near average over the Subpolar Gyre and central North Atlantic, whereas temperatures were generally higher than normal elsewhere around the margins and particularly so over the northern Barents Sea.
WGOH's findings form the basis of ICES Report on Ocean Climate (IROC), published annually. The data are available to visualize and download.
