Antarctic Ocean Temperature: Delayed Warming Due to ‘Deep, Old Water,’ Says Study

The temperature in the Southern Ocean, also called Antarctic Ocean, has remained cool - and has somehow gotten cooler - in the past decades. This had baffled scientists, considering the steady increase in temperatures elsewhere. A new study explains that the waters down south is experiencing delayed warming due to "old, deep water." 

"The oceans around Antarctica - if you look at temperature trends over the last 50 years - that's the one place that hasn't been showing a lot of warming," said Kyle Armour, professor of oceanography at the University of Washington and lead author of the study, as quoted on Popular Science. "It's actually shown a little bit of cooling in the last 30 years." 

According to the paper titled "Southern Ocean warming delayed by circumpolar upwelling and equatorward transport," the global mean sea-surface temperature went up by 0.08 degrees Celcius per decade since 1950, but the temperature in the area from the Antarctic Circumpolar Current to the South Pole rose by only 0.02 degrees Celcius per decade in the same period.   

While there are different theories that try to explain this phenomenon, the study says that background ocean circulation is the primary source of delayed warming in the Southern Ocean. 

Simply put, ocean waters travel along what is known as the global ocean conveyor belt, in which cold water in the north go downward to the bottom of the sea as it travels south, where it then rises to the surface. According to Popular Science, the water that is currently rising in the Southern Ocean was last exposed to the atmosphere before the Industrial Age in the 1700s; thus, it hasn't been affected by global warming. 

"The Southern Ocean is unique because it's bringing water up from several thousand meters [as much as 2 miles]," Phys.org quotes Armour as saying. "It's really deep, old water that's coming up to the surface, all around the continent. You have a lot of water coming to the surface, and that water hasn't seen the atmosphere for hundreds of years." 

This surface water then travels back north and, as it does, it absorbs heat, bringing warm waters to the Arctic. This results in faster warming in the northern region and delayed warming the Southern Ocean.   

Amour said that they are now moving away from the concept of global warming since the term suggests similar rates of warming across the planet; rather, they are moving toward the idea of regional warming, which, he explained, are shaped by the currents of the ocean. 

The study was conducted by the University of Washington and the Massachusetts Institute of Technology and published in Nature Geoscience last May.