In the Arctic Ocean, a new menace is slowly bubbling to the surface – warm water.
In a study published last week in Science, researchers found the Arctic Ocean – specifically the eastern Eurasian Basin near Scandinavia and Russia – is becoming more and more like the ice-free waters of the Atlantic Ocean as warm currents creep in. This “atlantification” has caused weaker stratification in the ocean’s unique water column, heating up the cold surface layer. The sudden shift has wide-reaching implications for everything from the ocean’s response to acidification to changes in nutrient productivity to sea ice loss.
Unlike the Atlantic and Pacific oceans, the coldest water layer in most of the Arctic Ocean lies at the surface. Warmer Atlantic waters are located farther down at intermediate depths and separated from the surface by the halocline layer, a thick, band of cold, salty water that prevents the two from mixing. But beginning in the 1970s, the halocline layer in the eastern Eurasian Basin began to weaken.
So between 2013 and 2015, researchers decided to use oceanographic moorings and drifting Ice-Tethered Profiler buoys to collect data on subsurface ocean temperature ranges and salinity. What they found was unprecedented. Since 2002, the difference in water temperatures between the layers dropped by roughly 1 degree Celsius (1.8 degrees Fahrenheit). Moreover, not only was the halocline layer weakening, in some months it disappeared entirely.
“In short, the basin used to be a three-layer cake, and now it’s a two-layer cake,” says Eddy Carmack, a coauthor of the study. “It’s quite remarkable that you’d see the architecture of the Arctic Ocean change just within a decade. It’s the kind of thing you’d expect over a 100-year time frame.”
Correspondingly, the eastern Eurasian Basin has been nearly ice-free at the end of summer since 2011. And the sea ice winter maximum has set a record low for three years running. Until now, sea ice loss in the Arctic has been associated with warmer air temperatures and the exacerbation of the albedo effect as more ice melts and the open ocean absorbs more heat from the sun. But now oceanographers believe this influx of Atlantic water is also playing a significant role in disappearing sea ice.
If this trend continues, there’s a strong possibility other basins of the Arctic Ocean will be “atlantified” as well.
“The processes in the Barents and Norwegian seas, the upstream locations for the Eurasian Basin, show the same tendencies as in the last decade,” says Igor Polyakov, lead author of the study. “We may expect that the atlantification of the eastern Eurasian Basin will continue, but whether it will go further eastward is yet to be seen.”
In addition to increasing the rate of sea ice loss, warmer waters may also mean greater nutrient productivity in the region. Whereas strong stratification previously restricted nutrient-rich waters of the Atlantic from moving upward, mixing will push more food to the surface.
But Carmack cautions that this is not necessarily a good thing. For example, zooplankton born in lower latitudes would arrive with “one foot in the grave,” unable to survive the Arctic environment.
Still, for the polar oceanographic community, the changes playing out are fascinating, if not unnerving. As the Arctic Ocean opens up, free of ice, it creates a testing ground for new experiments, management, policies, adaptation and mitigation that can later be applied to lower latitudes.
For Carmack, there’s a certain novelty about entering what he sees as the new age of the Arctic Ocean.
“It’s kind of like we started a second chapter in watching the sea ice melt story, and it extends deeper than just those first two to three meters of frozen water at the surface. Now, it’s starting to affect the entire water column.”
Never miss an update. Sign up here for our Arctic Deeply newsletter to receive weekly updates, special reports and featured insights on one of the most critical issues of our time.