There’s a pocket of warm water deep under the surface of the Canada Basin that could significantly melt the Arctic sea ice if it were to ascend far enough, according to a study, published today in Science Advances by researchers from Yale University and Woods Hole Oceanographic Institution.
“The most likely outcome for this heat is that it will slow the growth of winter sea ice, which further compromises the Arctic sea ice pack,” said Yale University researcher, Mary-Louise Timmermans, one of the authors of the study.
The Canada Basin is located in a large section of the Arctic Ocean known as the Amerasian Basin. west of Canada’s High Arctic Islands. The Amerasian Basin is one of the two major basins into which the North Polar Basin of the Arctic Ocean is split by the Lomonosov Ridge.
Covering 30 years of observations, researchers used older data from ships and newer data from permanent probes installed deep in the water of the Canada Basin to calculates there is currently enough new heat stored beneath the ocean surface to thin the ice cover of the entire basin by nearly a meter.
The study explains what has been going on. The researchers write that the significant warming seen in the Canada Basin is due to a circular ocean current called the Beaufort Gyre. The Beaufort Gyre is a wind-driven ocean current located in the Arctic Ocean polar region. The gyre contains both ice and water.
The Beaufort Gyre accumulates its fresh water by the process of melting the ice floating on the surface of the water as it pulls southern water north and under the Arctic’s ice.
A warming world and warming waters
First of all, we have known there is a layer of warm water deep below the Canada Basin, about 50 meters (164 feet) below the surface. The waters come from waters hundreds of kilometers to the south in the Chukchi Sea, said Timmermans. The waters are pulled North by the Beaufort Gyre.
Now, while warmer water usually floats because it’s lighter than cold water, this doesn’t happen in the Canada Basin. When the waters get that far north, their higher salinity makes them heavier than the water around them and they sink below the surface. The colder, fresher water stays at the top of the water column.
Scientists believe the warm water is coming from the edges of the basin, places like the Northern Chukchi Sea, where every summer sea ice melts and retreats. “That leaves a lot of open water exposed to the sun rays directly,” says Timmermans. And as climate change warms the waters even further, that heated water accumulates at the edge of the basin where it is pulled down below the surface.
“Unlike other oceans, where deeper layers tend to have colder temperatures, the Arctic has been known to have a warmer subsurface,” said co-author John Toole. But the sustained temperature increase in this warm layer was a surprise. Toole calls it “a ticking time bomb.”
“That heat isn’t going to go away,” he said. “Eventually … it’s going have to come up to the surface and it’s going to impact the ice.”
But Timmermans says there is no immediate threat. “That heat is very much insulated from the surface area,” she said. She explains that for heat to quickly affect other layers and the overlying ice, something would have to mix the layers, like a strong wind. “But wind input is largely buffered by sea ice cover sitting over top,” she said.
Then there is another possibility, according to the study. The salty waters could become so warm that they stop sinking and instead start mixing with the colder waters. The warmth under the ice hasn’t dipped or varied significantly since the 1980s, she added. It’s just kept marching upward “like a staircase.”
