The circular current, called the Beaufort Gyre, moves in a clockwise direction around the western Arctic Ocean, north of Canada and Alaska, where it naturally collects freshwater from glacial melt, river run-off and precipitation.
This freshwater protects sea ice from salty water which would melt it faster, and helps keep the north of the planet cool.
But increasingly rapid ice-melt due to climate change means the current has picked up unusually large amounts of freshwater and exposed it to the air, causing it to move faster and become more turbulent.
Using 12 years of satellite data, scientists have measured how this circular current has precariously balanced an influx of unprecedented amounts of cold, freshwater, and how this equilibrium could soon break down.
Since the 1990s, the gyre has accumulated a large volume of freshwater – 1,920 cubic miles (8,000 cubic km) – or almost twice the volume of Lake Michigan in the US.
The new study, published in Nature Communications, found the cause of this gain in freshwater concentration is the loss of sea ice in summer and autumn.
This long-term decline of the Arctic’s summertime ice cover has left the unfrozen sea much more exposed to the wind, which is therefore able to spin the gyre faster, trapping the freshwater in its current.
Persistent westerly winds have also dragged the current in one direction for over 20 years, increasing the speed and size of the clockwise current and preventing the freshwater from leaving the Arctic Ocean.
This decades-long western wind is unusual for the region, where previously the winds would change direction every five to seven years.
Scientists have been closely following the Beaufort Gyre in case the wind changes direction again.
If the direction were to change, the wind would then reverse the current, pulling it anticlockwise and releasing the water it has accumulated all at once.
“If the Beaufort Gyre were to release the excess freshwater into the Atlantic Ocean, it could potentially slow down its circulation. And that would have hemisphere-wide implications for the climate, especially in western Europe,” said Tom Armitage, lead author of the study and polar scientist at Nasa’s Jet Propulsion Laboratory in Pasadena, California.
This is because the release of the huge volume of freshwater from the Arctic Ocean into the north Atlantic could have a major effect on another vital ocean current system.
Freshwater is less dense than saltwater, so scientists fear the sudden release of thousands of cubic miles of freshwater could interfere with the current system known as Atlantic meridional overturning circulation.
This system keeps western Europe mild, due to the northward flow of warm, salty water in the upper layers of the Atlantic, and a southward flow of colder, deep waters.
Changes to this cycle could also affect the movement of organisms in the ocean, upon which many ecosystems depend.
“We don’t expect a shutting down of the Gulf Stream, but we do expect impacts. That’s why we’re monitoring the Beaufort Gyre so closely,” said Alek Petty, a co-author on the paper and polar scientist at Nasa’s Goddard Space Flight Centre.
The scientists said the results “reveal a delicate balance between wind and ocean as the sea ice pack recedes under climate change”.
“What this study is showing is that the loss of sea ice has really important impacts on our climate system that we’re only just discovering,” said Dr Petty.
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