The deep ocean waters of Antarctica are warming and shrinking, with potentially major consequences for climate and deep ocean ecosystems.
Larsen Fjord in the Weddell Sea, Antarctica. Photo: Sergio Pitamitz//VWPics/AP
The “Antarctic Bottom Water”—the body of water in the Southern Ocean surrounding Antarctica—is the coldest and saltiest body of water on the planet. It plays a key role in the ocean’s ability to absorb excess heat and carbon pollution. It also helps circulate nutrients across the ocean.
In the Weddell Sea, along the northern coast of Antarctica, this vital body of water is declining due to long-term changes in winds and sea ice, according to research released by the British Antarctic Survey (BAS) on June 12.
Using decades of data collected by ships and satellites, the team of scientists estimated the volume, temperature, and salinity of Antarctica’s deep waters. They found that the volume of the frigid waters had shrunk by more than 20 percent over the past three decades. They also found that water deeper than 2,000 meters (6,600 feet) was warming four times faster than the rest of the world’s oceans.
The new study suggests that the shrinking of deep water is due to changes in sea ice formation as winds weaken. Strong winds tend to push ice away from the ice shelf, leaving open water areas where more ice can form. Weaker winds mean these gaps are smaller, slowing the formation of sea ice.
The new sea ice is crucial to the formation of the extremely cold, salty water of the Weddell Sea. As the water freezes, the salt is forced out and, because salt water is denser, it sinks to the ocean floor.
Changes to these deep waters could have major consequences. They are an essential part of the global ocean circulation, transporting man-made carbon to deep waters where it is “locked up” for centuries, according to Alessandro Silvano of the University of Southampton, a co-author of the study.
If this cycle weakens, the deep sea could absorb less carbon, limiting the ocean’s power to reduce global warming. The oceans have absorbed more than 90% of the world’s excess heat since the 1970s and absorbed nearly a third of man-made carbon pollution.
The cold, dense waters also play a key role in oxygenating the deep sea. “We still don’t know how and if deep-sea ecosystems can adapt to lower oxygen levels,” Silvano added.
Thu Thao (According to CNN )
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