This was partly caused by the general warming of Atlantic Water in the North Atlantic Ocean. Additionally, a regional wind pattern indirectly strengthened a warm deep current that enters the Barents Sea from the north.
Protects ice cover
The warm deep current enters the Barents Sea from the Arctic Ocean. It flows into the Barents Sea below colder and fresher upper waters. The current is a branch of the Arctic Ocean Boundary Current that carries warm Atlantic Water below the cold surface waters through the Arctic Ocean. The branch enters the Barents Sea between Svalbard and Franz Josef Land. It carries warm Atlantic Water far into the Barents Sea. On its path through the northern Barents Sea the Atlantic Water gradually mixes with the cold waters above, such that the cold waters are warmed from below. The cold waters protect the ice cover on the surface from the warm Atlantic Water below. And more importantly, the cold waters protect the ice cover from the massive amount of even warmer Atlantic Water south of the ice edge.
The study argues that easterly winds along the Barents Sea shelf-slope will lead to a lift of the Arctic Ocean Boundary Current. This will increase the inflow of Atlantic Water to the Barents Sea. The study also shows that the regional wind pattern was favourable for easterly winds and increased inflow during the late 1990s and early 2000s. The easterly wind is part of the dipole pattern of near surface atmospheric pressure in the Arctic that was an unusual feature during this period. This is the first research article that links the regional wind with the cross-shelf exchange of Atlantic Water on the northern Barents Sea shelf.
The cold waters in the northern Barents Sea maintain a front against warmer and heavier water further south in the Barents Sea (the Polar Front). The Polar Front hinders the warm water further south from flowing into the northern Barents Sea. If the warm water could cross the Polar Front, the seasonal ice cover would not develop in winter. Thus the cold waters protect the seasonal ice cover of the Barents Sea. The warm Atlantic Water coming into the Barents Sea from the north may become a large threat to the ice cover. The Atlantic Water is not only warm, but also very saline. Thus, increased inflow of Atlantic Water from the north will increase the salinity and density of the cold upper waters. This will reduce the strength of the Polar Front; the warm water further south will start to cross the Polar Front; and the ice extent will be reduced. A substantial reduction of the ice cover will have large impact on the ecosystem, fisheries management, petroleum activity and shipping in the Barents Sea.