The Atlantic Ocean is invading the Arctic — and winning

The Arctic Ocean's boundaries are getting fuzzier as Atlantic waters push further northward and sea ice thins and melts more with each passing year, a new study finds.

Why it matters: If this trend continues, it could have wide-ranging impacts on lucrative marine fisheries, and may already be altering the weather patterns affecting your daily life in ways researchers are only now discovering.

The big picture: The Arctic is warming at a faster rate than any other region on Earth, and scientists have been documenting sweeping changes to the native ecosystems in this vast region. The fastest warming area of the Arctic is a remote expanse of stormy waters located north of Europe and Asia: The Barents and Kara Seas.

The basics: The Atlantic Ocean is well-mixed, with salty waters throughout the water column. In contrast, Arctic waters are stratified, meaning they have clearly separated layers — on top there is freshwater, which can be cooled down in the fall to form sea ice, and then replenished in the spring and summer, when the sea ice melts.

The boundary between the Arctic Ocean and the Atlantic Ocean is defined by this physical difference, said the study's lead author Sigrid Lind of the Institute of Marine Research in Norway.

What they did: Researchers extended a long-running set of observations meant to monitor the entire Barents Sea, which was taken using ship-based sensors aboard Norwegian and Russian research vessels. In total, the study relies on 76,000 temperature and salinity vertical profiles of the water column in the Barents Sea, all taken in the late summer and early fall. Of these, 18,000 profiles were from the central Barents Sea, and 7,000 were from the northern region. They also used surface observations from Norway and Russia, as well as sea ice data from the National Snow and Ice Data Center in Colorado. The data used for the study spanned the period from 1970 through 2016.

What they found: The regional "hot spot" of warming in these two seas is related to an oceanic invasion — the Atlantic Ocean is pushing farther north and east as the Arctic Ocean retreats.

• The observations pointed to a more well-mixed, hotter and less ice-covered region just in the five-year stretch between 2011-2016, as compared to previous years.
• The study found a sharp increase in the mixing and heat transport within the water column, and a decline in the freshwater present in the northern Barents Sea since 2010.

Between the lines: With less sea ice forming in and being transported to these two areas, there is less freshwater transport as well. This trend is key, because it allows the well-mixed Atlantic waters to make inroads into the frontier region of the Arctic, in turn discouraging the formation of more sea ice, and feeding an ongoing cycle.

Lind said the swiftness of the changes are noteworthy.

"Changes in the different parameters pointed in the same direction, towards some fundamental change, a shift in the climate. It was stunning to see that."

According to the study, rapid, fundamental shifts like what the study finds have previously only been observed in the record of historical climate. Now, it's playing out in real time, when monitoring networks are in place.

What's at stake: The Atlantic Ocean's inroads into parts of the Barents and potentially the Kara Sea as well, including areas in the Norwegian Arctic, means that fish species reliant on colder, less salty waters will likely move out of the region, disrupting the economy.

• Also, there are studies that find the hotspot in this part of the Arctic is having an influence on the weather thousands of miles away.
• Jennifer Francis, a researcher at Rutgers University, told Axios that the decline in sea ice and increase in air and ocean temperatures in this region is having clear downstream impacts. Francis was not involved in the new research.
• The "hot spot" in the Barents and Kara Seas tends to favor the formation of a ridge, or northward bulge, in the jet stream over that area, Francis said. This, in turn, can intensify an area of high pressure over East Asia.
• "The resulting amplified jet-stream wave then transfers wave energy upward into the stratosphere, which tends to disrupt the stratospheric polar vortex and prolongs the effects of ice loss and Atlantification well into late winter," Francis said.

What's next: As sea ice continues to decline, the Atlantic Ocean waters may push the polar front further north, effectively displacing the Arctic waters back toward the pole.