Globetrotting Swells

Globetrotting Swells

If it's pouring rain in New York, it might be sunny in Philadelphia. Yet the weather all around the world is interconnected. That's how a storm in the Arctic broke up an iceberg on the other side of the globe.


A frosty long-distance breakup. I'm Bob Hirshon and this is Science Update.

Last October, a storm in the Gulf of Alaska broke apart an iceberg more than twice the size of Los Angeles. More amazingly, that iceberg was off the coast of Antarctica, more than eight thousand miles away. In a new report, Northwestern University seismologist Emile Okal and his colleagues link the iceberg's breakup to a major ocean swell, which emerged from the violent storm and traveled for six days across the Pacific before it rocked the Antarctic ice.

Emile Okal:

This could represent a way of connecting two systems in the Earth, which, prior to this, might have been thought as being completely separate.

In fact, he says ocean swells from distant storms may break up polar ice all the time. But if global warming increases the frequency and intensity of such storms, it could accelerate the process. I'm Bob Hirshon, for AAAS, the science society.

Making Sense of the Research

It's not news to say that weather around the world is interconnected. Thanks to satellite radar, you can watch a storm cross the country on any television or Internet weather report. The movement of that storm depends, in part, on the movement of other air masses around it, which move in from different parts of the globe. In addition, other natural phenomena can generate dramatic effects across distances: for example, an undersea earthquake may cause a tidal wave, or tsunami, that travels thousands of miles and devastates coastal areas.

So what's new here? Aside from the enormous distance between the storm and the ice breakup, this finding connects two systems that would otherwise seem to be unrelated. It's relatively simple to see the earthquake-tsunami connection: An earthquake rocks the sea floor and creates a big wave. But it's more of a leap to imagine a storm breaking up an iceberg halfway around the world.

The scientists discovered the connection accidentally. They had installed seismometers (instruments that measure vibrations and movement) around the icebergs for a completely separate research project. Although the weather on the day the iceberg broke up was calm, these instruments detected that the iceberg shifted around both before and after it broke apart: half an inch up and down and four inches side to side.

It takes a strong force to move a giant iceberg that much—usually an ocean swell. And generally, swells are caused by storms. But where was the storm? It turns out scientists can calculate this by comparing the different kinds of waves detected by the seismometer. Waves with long wavelengths travel faster than waves with short wavelengths. If a storm is very close by, both kinds of waves will show up at nearly the same time. But the longer the waves have to travel, the longer it will take for the short waves to catch up to the long waves.

Confused? Then picture this: Two brothers leave their house at the same time: one in a car and one on a bike. If they're just going to the end of the block, they'll get there at almost the exact same time. But if they're going to a store a mile away, the car might beat the bike there by a couple of minutes. And if they're going to visit a relative 100 miles away, the guy in the car will arrive hours earlier. In fact, if you knew exactly how fast the car and the bike traveled, you could calculate the distance between their house and their destination from the lag time between the car and the bike's arrival. Swap "long wave" for "car" and "short wave" for "bike," and you've got the idea.

Once the scientists ran their calculations, they were shocked at how far away the storm appeared to be: 13,500 kilometers (about 8,300 miles)! But sure enough, when they looked at the weather records, they found a storm in Alaska at exactly that distance had happened six days earlier. Using data from buoys in the ocean, which bob up and down as the ocean swells, they were able to track the swell's journey from Alaska to the Antarctic, by way of Hawaii.

This goes to show that natural systems can be related in ways you may not expect: something every aspect of science has discovered over and over again. It also suggests that global warming may have an additional “domino effect” that scientists hadn't thought of: if warming temperatures cause more storms, as they are expected to do, it's possible that icebergs could break up faster as well. Those breakups could make the ice melt more quickly and efficiently, further contributing to the rising sea levels we're expecting in the future.

Now try and answer these questions:

  1. What are the two systems that were connected in this research?
  2. How did the storm in Alaska cause the Antarctic iceberg to break up?
  3. How did the scientists determine this?
  4. Can you think of other systems—in science or everyday life—that appear to be unrelated, but are actually connected?

You may want to check out the November 17, 2006, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: whiskers could help robots feel, how bee brains are like human brains, a genetic disorder with musical gifts, how a storm at the North Pole damaged an iceberg at the South Pole, and what science is telling scholars about the Dead Sea Scrolls.

For Educators

The National Geographic Video News article, Huge Iceberg Crumbles off Antarctica, shows the actual breakup of iceberg B15.

The PBS Nova feature, Warnings from the Ice, discusses the potentially devastating impact of disappearing polar ice sheets.

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