Climate heating has reached even deepest parts of the Arctic Ocean

Warm Atlantic water from Greenland warms the depths Arctic Oceanwhich was previously considered one of the few places not significantly affected by climate change.

Sea ice at the top of the Arctic Ocean has declined by about 40 percent over four decades, largely due to the effects of atmospheric warming on the ocean surface. Now researchers from the Ocean University of China have analyzed recent measurements taken by icebreakers to estimate warming on the ocean floor.

In one of the two largest ocean basins – the Eurasian – since 1990, waters at depths of 1500 to 2600 meters have warmed by 0.074°C.

While that doesn't sound like much, it represents a transfer of nearly 500 trillion megajoules of energy. If this amount of energy were present at the surface, it could melt up to a third of the minimum sea ice area.

“The deep ocean is much more active than we thought,” says Xianyao Chenmember of the research team. “I thought the deep ocean might be warming, but not that fast.”

An underwater mountain range running between Greenland and Siberia divides the Arctic Ocean into two basins. Although the Amerasian Basin is largely separated from the Pacific Ocean by the shallow Bering Strait, which is a continuation of the Pacific Ocean. Atlantic meridional overturning circulationor AMOC, carries warm Atlantic waters north along the Scandinavian coast and into the upper layers of the Eurasian basin. When seawater freezes in winter, the salt it contains is released from the crystals. This creates dense water that sinks to depth, taking with it some of the warm water from the Atlantic.

geothermal heat The Earth is also warming the deep waters of the Eurasian Basin.

Previously, these warming processes were offset by the influx of cold deep water from the basin immediately east of Greenland. But as the Greenland ice sheet melts, more fresh water is entering the Greenland basin. This slowed the sinking of cold, salty water to depth and helped raise the temperature of deep water in the Greenland basin from -1.1°C to -0.7°C – one of the fastest rates of warming in the deep ocean. As a result, the movement of Greenland's deep waters into the Arctic Ocean no longer compensates for geothermal bottom heat and the sinking of warm Atlantic waters.

“Warming of the Greenland basin has spread to the Arctic,” says Ruizhe Songpart of the research team.

The study showed a new warming process in the deep Arctic Ocean, “linked to global warming in yet another place,” he says. James McWilliams at UCLA.

This warming could eventually contribute to the melting of sea ice or even the melting of permafrost underwater, he adds. Permafrost includes ice-like deposits known as clathrates, which, if disturbed, can release methane into the atmosphere, a process that is believed to have caused the Permian mass extinction.