Why Antarctic Ocean hasn’t warmed when the rest of the world has?

Is the deep, old water the reason for the Antarctic Ocean hasn't warmed?

Human-driven activities have adversely affected the climate. However, waters surrounding Antarctica are not much affected.

New research from the University of Washington and the Massachusetts Institute of Technology finds that ocean currents explain why the seawater has stayed at roughly the same temperature while most of the rest of the planet has warmed.

"With rising carbon dioxide you would expect more warming at both poles, but we only see it at one of the poles, so something else must be going on," said lead author Kyle Armour, a UW assistant professor of oceanography and of atmospheric sciences. "We show that it's for really simple reasons, and ocean currents are the hero here."

Phenomenon: Gale-force westerly winds that constantly whip around Antarctica act to push surface water north, continually drawing up water from below. The Southern Ocean's water comes from such great depths, and from sources that are so distant, that it will take centuries before the water reaching the surface has experienced modern global warming.

"The Southern Ocean is unique because it's bringing water up from several thousand meters [as much as 2 miles]," Armour said. "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."

The Antarctic Ocean's waters delay in warming but the culprit had been wrongly identified as churning, frigid seas mixing extra heat downward. The study used data from Argo observational floats and other instruments to trace the path of the missing heat.

"The old idea was that heat taken up at the surface would just mix downward, and that's the reason for the slow warming," Armour said. "But the observations show that heat is actually being carried away from Antarctica, northward along the surface."

In the Atlantic, the northward flow of the ocean's surface continues all the way to the Arctic. "The oceans are acting to enhance warming in the Arctic while damping warming around Antarctica," Armour said. "You can't directly compare warming at the poles, because it's occurring on top of very different ocean circulations."

This study will help in predicting the temperatures in future.

"When we hear the term 'global warming,' we think of warming everywhere at the same rate," Armour said. "We are moving away from this idea of global warming and more toward the idea of regional patterns of warming, which are strongly shaped by ocean currents."