Warmer Atlantic water originating near Greenland is causing unexpected heating in the deepest parts of the Arctic Ocean. Researchers have found that waters in the Eurasian basin have warmed by 0.074°C since 1990, transferring vast amounts of energy. This development implicates global warming in yet another remote ocean region.
The Arctic Ocean, long considered somewhat insulated from climate change's worst effects, is now experiencing warming in its deepest layers. According to a study by researchers from the Ocean University of China, warmer Atlantic water from near Greenland is penetrating the depths, particularly in the Eurasian basin.
Sea ice on the Arctic Ocean surface has shrunk by about 40 percent over four decades, mainly due to atmospheric warming. Now, analysis of recent icebreaker measurements reveals that waters between 1,500 and 2,600 meters deep in the Eurasian basin have warmed by 0.074°C since 1990. This seemingly small increase represents the transfer of almost 500 trillion megajoules of energy—enough, if at the surface, to melt a third of the minimum sea ice extent.
"The deep ocean is much more active than what we thought," says Xianyao Chen, a member of the research team. "I thought the deep ocean could be warming, but not so fast."
An underwater mountain range separates the Arctic Ocean into the Eurasian and Amerasian basins. Warm Atlantic water enters via an extension of the Atlantic Meridional Overturning Circulation (AMOC) along Scandinavia's coast. During winter freezing, ejected salt creates dense water that sinks, carrying this warmth downward. Geothermal heat from Earth's interior also contributes.
Previously, cold deep water from east of Greenland offset these effects. However, melting of the Greenland ice sheet introduces freshwater, slowing the sinking of cold, salty water. This has raised deep water temperatures in the Greenland basin from -1.1°C to -0.7°C—one of the fastest deep-ocean warming rates. Consequently, less cold water reaches the Arctic, allowing geothermal and Atlantic warmth to dominate.
"The warming of the Greenland basin has extended to the Arctic," says Ruizhe Song, part of the research team.
James McWilliams at the University of California, Los Angeles, notes this reveals a new heating process, linking global warming to another location. It could eventually accelerate sea ice melt or thaw sub-sea permafrost, potentially releasing methane from clathrates—a risk hypothesized in past mass extinctions.
The findings appear in Science Advances (DOI: 10.1126/sciadv.adx9452).