The warm Gulf Stream is kept cold. The Barents Sea is a cooling machine. To predict how ocean currents will develop in the Atlantic, one needs to know what drives them. The search for driving forces led researchers to track warm waters from the Gulf Stream farther north.
In a new study published in the journal Oceanographic Sciences, Jakob Dohr and colleagues from the Bjerknes Centre, the University of Bergen, the Nansen Center for Environment and Remote Sensing, Stockholm University, and the UK’s National Oceanographic Centre, looked at what happens to the water that flows from the Atlantic Ocean into the Arctic Ocean.
Reduced sea ice cover in the Arctic may limit the decline in ocean currents in the south.
The Gulf Stream is one component of a larger system of currents called the Atlantic Overturning Circulation (AMOC). The word upwelling refers to the movement of water both vertically and horizontally, as in a ring or conveyor belt between a surface and an abyss.
Whether climate change might reduce the Gulf Stream has been a recurring topic in international news media. The real question concerns possible changes in the Atlantic overturning circulation, not a single surface current, but the entire circulation.
An overturn involves warm water being pushed northward by winds before the water cools, becomes denser, and sinks. Then the water returns south in depth. In some areas, the water becomes denser because salt is released from the frozen ice. But the key to sinking is cooling of the surface water.
As the climate changes, the water in the northern regions will cool less, while more meltwater and rain make the sea fresher. Both factors make the water less dense, reducing the sinking that contributes to the loop’s continuation. The decline in depth of the waters returning south will in turn affect the flow of warm water from the Gulf of Mexico across the Atlantic towards northern Europe and Norway.
Questions about the future of the Gulf Stream are determined by climate changes in the north. But where is the north?
In fact, the currents in the Atlantic Ocean do not follow a single ring, but rather spread like a multi-branched blood stream. The North can map many sites along these branches, but some areas are more important than others.
Originally, it was thought that most of the water would sink into the Labrador Sea. Later, it turned out that the northern seas were no less important. In recent years, researchers like Dor have looked further north: toward the Arctic Ocean.
Climate theory and models suggest that the Atlantic overturning circulation will decrease in the future, and the Norwegian Sea is one of those areas that will contribute less to its preservation. It is unclear whether Norway will receive less heat from the south.
It is possible that new regions will take over some of the role played by the Norwegian Sea and other cooling regions.
One hypothesis is that decreasing sea ice in the Arctic Ocean may open up new areas where water can sink, thus counteracting some of the weakening of the overturning circulation.
“I think it could make a difference in what we see in Norway, that is, anywhere north of Iceland,” Dorr says, although he stresses that the final outcome is uncertain.
“We know very little about the Arctic Ocean,” he continues. “There are very few observations about the deep Arctic.”
In order for Dor and his colleagues to track the movement of water in and out of the Arctic Ocean, they used a computer model to simulate ocean currents. They explored conditions as they are now, and the knowledge required when considering possible future changes.
