The deep ocean waters in Antarctica are warming and shrinking, potentially causing significant consequences for the climate and deep ocean ecosystems.
“Antarctic Bottom Water” – the body of water in the Southern Ocean surrounding Antarctica – is the coldest and saltiest water on the planet. This water plays a crucial role in the ocean’s ability to absorb excess heat and carbon pollution. Additionally, it helps circulate nutrients across the ocean.
Larsen Strait in the Weddell Sea, Antarctica. (Photo: Sergio Pitamitz//VWPics/AP)
In the Weddell Sea, along the northern coastline of Antarctica, this important body of water is declining due to long-term changes in wind and sea ice, according to research published by the British Antarctic Survey (BAS) on June 12.
The research team utilized data collected by ships and satellites over decades to assess the volume, temperature, and salinity of Antarctic Bottom Water. They found that the volume of this frigid water has decreased by more than 20% over the past three decades. They also noted that water deeper than 2,000 meters is warming four times faster than the rest of the world’s oceans.
The new study indicates that the shrinking of deep water is linked to changes in sea ice formation as winds weaken. Strong winds tend to push ice away from the ice shelf, leaving open water areas that allow for more ice formation. Weaker winds mean these gaps are smaller, slowing down the sea ice formation process.
New sea ice is crucial for the formation of the extremely salty and cold water in the Weddell Sea. When water freezes, salt is expelled, and due to the denser saline water, it sinks to the ocean floor.
Changes in these deep waters could have significant consequences. They are an essential component of the global ocean circulation, transporting the carbon produced by humans down to the deep waters, where carbon is “trapped” for centuries, according to expert Alessandro Silvano from the University of Southampton, a co-author of the study.
If this circulation weakens, the deep ocean may absorb less carbon, limiting the ocean’s capacity to mitigate global warming. Oceans have absorbed more than 90% of the world’s excess heat since the 1970s and nearly one-third of human-caused carbon pollution.
Cold and dense water also plays an important role in providing oxygen to the deep sea. “We are still unclear how, or if, deep-sea ecosystems can adapt to lower oxygen levels,” Silvano added.
