Underwater robot 'dolphins' offer clues to Antarctic melt

Warm waters are melting Antarctica's ice sheet at an unprecedented rate, but scientists have been unsure how such warm water is finding its way to one of the coldest regions of the planet. Until now.

|
Alan Jamieson/Caltech
Oceanographers Liz Creed of Kongsberg, Inc. and Andy Thompson of the California Institute of Technology run through a series of tests in preparation for the release of a Seaglider into the Weddell Sea in January 2012.

In recent years, environmental scientists have warily watched as the ice sheet on the coast of West Antarctica has begun melting at unprecedented rates. In May, NASA glaciologists declared that the catastrophic melt of the ice sheet  to be “unstoppable.” Researchers have long believed that warm waters were somehow whittling away at the ice sheet, but little was understood about how such warm water made it to one of the coldest regions of the world.

With the help of some underwater robots, researchers at California Institute of Technology have pieced together the most detailed picture to date of what might be happening beneath the surface of the Southern Ocean. The team published their findings online Monday in the journal Nature Geoscience.

Typically, oceanic temperature measurements are gathered via satellite or from temperature buoys towed by ships. Neither are particularly viable methods around Antarctica.

“Observationally, it’s a very hard place to get to with ships,” lead author Andrew Thompson said in a press release. “Also, the warm water is not at the surface, making satellite observations ineffective.”

That’s where robotic ocean gliders come in.

These six-foot-long torpedo shaped drones, which resemble robotic dolphins, use very little energy and can traverse the ocean depths for long periods of time, bobbing to the surface every few hours to “call home” and transmit data to researchers.

In recent years, corporations, research institutions, and even the military have used similar underwater drones to explore the ocean. Fossil fuel companies use autonomous subs to map the ocean floor in search of hidden oil and gas reserves. Researchers at the University of Delaware and Delaware State University have employed remote-controlled, underwater gliders to study elusive sand tiger sharks in the Delaware Bay. And earlier this year, the US Navy sent an American-made underwater drone to aid in the search for the missing Malaysian airliner that is believed to have crashed into the Indian Ocean in March.

Professor Thompson’s gliders spent two months traversing the coast of the Antarctic Peninsula collecting temperature and salinity data beginning in January 2012. While the ultimate goal of the mission was to study thermal transport, salinity levels play a major role in the way waters of differing temperatures flow, the Caltech professor of environmental science and engineering explained.

In fresh water, warm water always rises to the top of the water column, just as heat rises in the atmosphere. However, the presence of salt in the water can alter the stratification of the water column, especially along the coast where fresh melt water mixes with saline ocean water. The melt water coming off the coastal shelf is very cold, just above freezing, but has a much lower salt content than the ocean water so it remains suspended at the surface.

In this region, the warmest waters actually float suspended in a middle layer of the water column. “That’s the layer that is actually moving toward the ice shelf,” Thompson said.

By analyzing data gathered by the gliders, the researchers determined that warm layer was being transported from warmer latitudes by swirling eddies. Eddies behave similarly to atmospheric storms, but whip water instead of winds. They serve a vital function of helping to churn nutrients from the bottom of the ocean up to the surface. In this case, they also deliver warm water from warm latitudes toward the pole.

While ships frequently observe eddies – oceanographers actually name each one just as meteorologists name hurricanes – they typically only glimpse them briefly because the Southern Ocean is treacherous: The weather is fierce and expeditions are extremely costly. However, Caltech’s gliders were able to spend much longer monitoring the eddies at work than a ship typically could.

“Ocean currents are variable, and so if you go just one time, what you measure might not be what the current looks like a day later. It’s sort of like the weather – you know it’s going to be warm in the summer and cold in the winter, but on a day to day basis it could be cold in the summer just because a storm came in,” Thompson said. “Eddies do the same thing in the ocean, so unless you understand how the temperature of currents is changing from day to day – information we can actually collect with the gliders – then you can’t understand what the long-term heat transport is.”

Thompson hopes that future missions that gather both oceanic and atmospheric data will provide clues into the transfer of carbon dioxide between the sea and air. 

You've read  of  free articles. Subscribe to continue.
Real news can be honest, hopeful, credible, constructive.
What is the Monitor difference? Tackling the tough headlines – with humanity. Listening to sources – with respect. Seeing the story that others are missing by reporting what so often gets overlooked: the values that connect us. That’s Monitor reporting – news that changes how you see the world.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to CSMonitor.com.

QR Code to Underwater robot 'dolphins' offer clues to Antarctic melt
Read this article in
https://www.csmonitor.com/Science/2014/1111/Underwater-robot-dolphins-offer-clues-to-Antarctic-melt
QR Code to Subscription page
Start your subscription today
https://www.csmonitor.com/subscribe