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Currents Are the Secret to an Antarctic Climate Change Mystery

But just because you can't see it, doesn't mean it's not happening.

by Sarah Emerson
Jun 2 2016, 12:00pm

Mackenzie Bay, Antarctica. Image: NASA Goddard Space Flight Center

Is Antarctica melting or not? This question has been asked time and time again by scientists and climate change deniers alike. Climate models and ice records have shown that for some reason, warming in the Southern Ocean is happening at a significantly delayed rate.

For skeptics, Antarctica's sea ice growth in the face of global warming has provided false ammunition against the existence of anthropogenic climate change. But for scientists, the southernmost continent's seeming resilience has offered an invaluable opportunity to examine a relatively untouched ocean ecosystem before it succumbs to rising temperatures.

Antarctic ice maximums. GIF: YouTube/NASA Goddard

A study published this week in Nature Geoscience provides new insights into why the waters surrounding Antarctica stand to be the last places on Earth affected by climate change. What researchers discovered was that centuries-old ocean currents—seawater that hasn't touched the planet's atmosphere since long before the Industrial Revolution—are responsible for keeping the Southern Ocean cold. For now.

"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," lead author Kyle Armour, an assistant professor of oceanography and atmospheric sciences at the University of Washington, said in a statement. "We show that it's for really simple reasons, and ocean currents are the hero here."

Diagram of the different water masses in the Southern Ocean. Image: Wikipedia

According to the team of climate scientists from the University of Washington and the Massachusetts Institute of Technology, Antarctica's unique currents and strong westerly winds are constantly dredging up ancient currents from deep beneath the ocean's surface. In some areas, these currents rise from a depth of up to two miles. At the same time, existing surface heat is carried northward by gale-force torrents, causing Earth's northernmost pole to shoulder most of the weight of global warming.

It will take centuries before the waters upwelled from Antarctica's depths ever experience the effects of climate change, the study notes.

Previous theories have suggested that persistent, churning seawater was responsible for mixing heat downward, instead of dispersing it outward. However, the study's findings and climate simulations show that surface warming is actually being transported northward.

GIF: YouTube/NASA Goddard

The researchers hope their conclusions will shed more light on why northern ice sheets are melting at such an accelerated rate compared to other parts of the world.

"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."

Unfortunately, the term "global warming" can lead us to think that it's happening at the same pace everywhere, and in similar ways. And if an ecosystem isn't showing immediate signs of damage, then it might be immune altogether. But as studies like this show, we'd be wise to heed the deceptively slow creep of climate change.