Anyone who has spent time on a beach can visualize rolling waves, breaking as they approach the shoreline. What most probably don’t realize, is the same thing happens out of sight, deep under the ocean surface – but on a massive scale.
Picture this: a giant wave, close to 1,000 feet tall, spanning more than 50 miles – that is the scale we’re talking about, and it’s happening thousands of feet underwater.
“If you’ve ever seen the office toys that have a layer of blue fluid and a layer of clear fluid, and you can rock them back and forth and see these very slow-moving undulations,” Harper Simmons, an associate professor of oceanography at the University of Alaska Fairbanks, said. “That is exactly the phenomena we’re talking about.”
He’s been studying these massive, undersea waves for over a decade.
Since 2007, Simmons has been taking part in a study in the South China Sea, with researchers from 25 institutions from five countries, taking a closer look at how these waves work.
Even though the movement of these waves appear similar to a waves on the surface, he says there are some differences.
“They move at approximately three meters per second, whereas a surface wave might move at 10 or 20 times that rate,” Simmons said. “So they’re massive waves; they contain huge amounts of energy, but they evolve in slow motion relative to what we would see at the surface.”
But why are these waves so important?
Big waves create big turbulence, and Simmons says that’s what makes them vital.
“And anywhere you can have strong turbulence, you can bring up fresh nutrients from depth,” he said. “And, so these waves have profound effects on ecosystems.”
By redistributing the deep-sea nutrients closer to the surface, the waves help replenish the shallower parts of the ocean where much of the biological activity takes place.
Undersea waves require ocean stratification in order to form – meaning layers of water, defined by differences in salinity and temperature. If stratification exists, Simmons says the other primary ingredient is usually tidal action moving over submarine ridges, islands, and other types of underwater topography, which means these waves are forming all over the world – including Alaska.
“A place like Prince William Sound, a fjord, is highly stratified and there’s very significant tides,” Simmons said. “So we expect that the larger fjords, such as Prince William Sound, would be absolutely filled with these things.”
Not much research has been done on Alaska’s sub-surface waves, but Simmons says researchers do know they form in the Arctic Ocean – albeit in a weaker form.
“One of the main energy sources for these are from storms in the Arctic,” Simmons said. “And the ice kind of an insulating barrier to prevent that kind of energy from being put into the ocean.”
Simmons says researchers are interested to see if the Arctic dynamic changes as the area continues seeing reduced sea ice, seasonally.
The study of internal waves in the South China Sea was summarized in an article published in the May 7th issue of Nature.