Scientists have been puzzled why the waters around Antarctica remained cold despite the fact that human-caused climate change has heated up the rest of the world's oceans.
While the average global sea-surface temperature has increased by 0.08 C per decade since 1950, research has shown that the Southern Ocean's surface temperatures have only increased by 0.02 C.
Findings of a new study, however, have shed light on why the temperature of Antarctic seawater stayed about the same while the rest of the planet has mostly warmed.
Using climate models and observations, Kyle Armour, from the University of Washington, and colleagues have found that the unique currents around Antarctica cause centuries-old water to go up the surface transporting warmer water on the surface to the equator.
The last time this old seawater touched the atmosphere was before the machine age and thus did not experience man-made climate change that is largely blamed on fossil fuels.
"Delayed warming south of the Antarctic Circumpolar Current and enhanced warming to the north-are fundamentally shaped by the Southern Ocean's meridional overturning circulation: wind-driven upwelling of unmodified water from depth damps warming around Antarctica," the researchers wrote in their study published in the journal Nature Geoscience on May 30.
Unlike other oceans such as those in the equator and the west coast of Americas where seawaters are drawn up from a few hundred meters below, seawaters drawn up in the Southern Ocean come from great depths and distance.
This means that the water has not seen the atmosphere for a while nor has it experienced modern global warming.
The deep, old waters that go up the surface off Antarctica saw the Earth's atmosphere in the North Atlantic centuries ago. This water then sank and went through circuitous paths around the world's oceans before it resurfaced off Antarctica up to thousands of years later.
"The Southern Ocean is unique because it's bringing water up from several thousand meters [as much as 2 miles]," said Armour.
"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."
Man-made-caused climate change is largely attributed for the warming of the oceans that leads to rise in sea levels, a phenomenon that experts fear could swallow islands. Researchers have found that between the 1900s and the 2000s, seawater levels have risen by up to 1.4 millimeters per year.
