This layered structure was “remarkably stable” from 1970 all the way through 2011, the team notes. However, signs of change could be seen even as these layers persisted — atmospheric temperatures over the Arctic have seen a steady rise, warming faster than any other region on Earth. This contributed to a dramatic decline in ice cover throughout the Arctic Ocean, reaching then-record lows in 2007 and 2008.
Because there wasn’t any ice to flow south, the Barents remained relatively ice-free during the Arctic summer. Average sea-ice drift into the Barents in 2010-2015 was 40% lower than the 1979-2009 mean, the team writes. Right now, it’s completely ice-free, despite the fact that the melt season historically lasts through to September. The team also checked precipitation levels on islands bordering the Barents Sea, such as Svalbard and Franz Josef Land, to confirm that the loss of fresh water came down to loss of ice, not a change in weather patterns.
Ocean heat content in the northern Barents Sea, observed during 1970–2016.
Image credits Lind et al., 2018, Nature.
The sea’s surface layer rapidly declined in the absence of ice to insulate it. The top 100m of water has heated up dramatically over the past few years, according to the team. Mean temperatures between 2010 and 2016 were nearly four standard deviations higher than the 1970-1999 mean. In 2016, they were 6.3 standard deviations higher.
Sandwiched between two warmer bodies of water, the intermediate layer has also been heating up. The team reports that starting with the late 2000s, the entire water column has both warmed and gotten saltier. The intermediate has now all but vanished from the Barents Sea, the team notes, which is now dominated by water flowing in from the Atlantic. Even worse, warmer waters with higher salt content make it extremely difficult for sea ice to re-establish itself during winter.
“Increased Atlantic Water inflow has recently enlarged the area where sea ice cannot form, causing reductions in the sea-ice extent,” the team writes.
“The entire region could soon have a warm and well-mixed water-column structure and be part of the Atlantic domain.”
While it may not sound like a big deal to us, from an ecosystems point of view, these changes are immense. The authors describe the Barents as “divided into two regions with distinct climate regimes—the north having a cold and harsh Arctic climate and ice-associated ecosystem, while the south has a favorable Atlantic climate with a rich ecosystem and lucrative fisheries”. Now, however, it’s becoming one big Atlantic climate ecosystem.
The findings help provide some context as to the sheer scale of changes such tipping points can usher in — and how fast they can do so. The team says we’re likely to see a lot of regional tipping points such as this one, not a single, planet-spanning super tipping point. The future, however, will be built on the sum of these events and the way they interact — making it extremely hard to predict just what that future will look like.
The paper “Arctic warming hotspot in the northern Barents Sea linked to declining sea-ice import” has been published in the journal Nature.
