7 December 2012
Whirlpools created at the edges of breaking waves can influence how ocean nutrients – and pollution – get mixed about in the ocean.
Until now, this swirling has been a theory seen only in computer simulations. David Clark, a postdoctoral researcher at Woods Hole Oceanographic Institution in Woods Hole, Mass., wanted to see if he could physically measure a vortex created by waves off the coast of Duck, N.C.
Clark, who presented a poster Tuesday morning the American Geophysical Union’s 2012 Fall Meeting, confirmed that individual waves can create these spinning eddies.
A breaking wave slams downward, churning water and leaving a frothy residue of foam and bubbles. But it’s the less noticeable outer edges of waves that interest Clark. “It’s not the stuff that you see, it’s the big motions you can’t see that are actually doing most of the mixing,” says Clark.
However, the surf zone was a difficult place to put out expensive scientific equipment to track this spinning water.
“We’re working in a sandy beach, so we can’t bolt anything down,” says Clark, who put out 10 sensors in the surf zone to measure the pounding of breaking waves.
Clark used a machine called a jetter, which he describes as an ultra-powerful fire hose, to blast an 8-foot deep hole into the sandy ocean. He jammed 10-foot long steel pipes into the craters and mounted wave-measuring gadgets onto the poles.
When the outer ends of a breaking wave smash down on the ocean, they send water spiraling off sideways that create strong eddies. Clark even found weaker whirls of water in the center of breaking waves.
“In terms of pollution, the faster it spreads, the more shoreline it affects,” says Clark, who is the first to track the speed of this spinning with real waves.
Clark, who ran the pilot study for 12 hours, plans to carry out a bigger study with more sensors in order to compare the rotating water when waves break at low and high tides. He hopes this will give him more information on how different ocean conditions can spread pollutants.
-Ryder Diaz is a science communication graduate student at UC Santa Cruz