An Abundance Of Ocean Eddies Are Shown In New Space Radar Movies
Ocean Goldilocks eddies, swirling bodies of water 100 kilometers (60 miles) across, are now watchable as radar moves from satellites. These vital just right ocean features are among the most important features in the worlds oceans as they are the nurseries and pastures for the majority of ocean fish. Oceanographers know them as being the Goldilocks Zone for ocean life, mesoscale eddies, not too big not too small.
We know these ocean Goldilocks eddies well as our work on ocean pastures has long recognized these marvels of the ocean environment for the vital role they serve as ocean nurseries and feeding grounds. Because they stay together we make use of ocean eddies as naturally controlled and contained testing areas that exhibit powerful sustaining ecological forces.
They are vast pastures contained by natural boundaries. Once consistently vibrant with ocean life they are increasingly becoming depleted due to deprivation and limitation of vital mineral micronutrients.
They are (or ought to be) the gardens of the seven seas. Like any garden they benefit from care and attention and when they receive it a healthy garden sustains itself for a long time following a small amount of help. Here’s a glimpse at our story of becoming stewards of a large ocean eddy in the summer of 2012.
They spin up as a result of ocean the interaction of ocean currents, winds, and tides then slowly over time frames of many months gyrate their way across the sea at a snails pace—3 miles per day. Oceanographers call them mesoscale eddies, we call them Goldilocks eddies, for their middle size, larger than a wake formed by an aircraft carrier and smaller than a giant ocean gyre.
Depending on whether they are spinning up or down, held together by their rotation, they may be like a fountain of deep water rising to the surface or a whirlpool slowly sucking water into the abyss. The and extending from a few hundred to a thousand meters beneath the surface.
In the video above, eddies show up as red and blue dots dancing around. (Red ones spin clockwise, blue ones counterclockwise.) Just like the swirling water in a sink as it drains, depending on which hemisphere of the world they are in they may be up-welling mountains or down-welling whirlpools.
The amount of water carried around by all these eddies is staggering. It’s more than 30 times the volume that flow from the world’s rivers into the ocean, according to a paper published today in Science. As such its no wonder they are perhaps the most important environment on this blue planet.
Everything in the ocean in the vicinity of an eddy ends up caught by or is attracted to these marvelous ocean merry go rounds. Once the whirl begin life goes for a grand free ride. The paper reveals a startling number of eddies that concentrate nutrients and as such are the typically vibrant oases in otherwise desert like ocean regions.
These eddies are so vast being below the surface are invisible unless you look from space with radar altimetry. For decades, oceanographers have been tracking eddies using NASA satellites. By bouncing a pulse of radar off the surface of the water and recording the time it takes to return. The satellites can measure their distance from the water to within less than a centimeter. This astounding accuracy turns out to be necessary, since unlike the ship-swallowing whirlpools of Greek mythology, the depression at the center of an eddy is a mere half a meter below the distant edge some 50 kilometers away.
To reconstruct the 3-D structure of the eddies and find their volume, a team of oceanographers led by Bo Qiu of the University of Hawaii used data from underwater floats. More than 3,000 ARGO submersibles are scattered around the globe, lurking under the surface. Each comes to the surface every 10 days to report the water temperature, salt content, density, and velocity.
An eddy, once born, might travel for months or years before dissipating. By combining a decade of satellite and submersible data, the researchers were able to track the incredible mass of water collectively moved by eddies across the entire world. Qiu’s calculations surprised even him.
“We didn’t expect the number to be that high,” he said. “We know they propagate westward, and there are a lot of eddies. But the mass… there’s an order of magnitude more than we expected.”
Until recently it has been mistakenly taught that the steady currents like the Gulf Stream were almost entirely responsible for transport of bodies of water and what it holds across oceans. But eddies are at least as important if not more in that role.
The transportation of ocean nutrients, dissolved carbon dioxide and heat all around the world relies heavily on eddies. The latter two are important for understanding climate change. Qiu’s study raises the possibility that eddies also make a substantial contribution to these transports.
This paper is sure to create a swirl of research among climate modelers, says Ryan Abernathey, who studies the impact of ocean circulation on climate at Columbia University. ”The volume estimate is really surprising,” he said. “This is an important effect. The next question is how leaky the eddy is.”
The eddy is liquid after and the difference between inside and outside is not precise. If, say, the dissolved carbon caught in an eddy slowly slips out, then after a year of gyrating an eddy may have spread some of its original contents an ocean away. But if the eddies hold tight to their contents, they might be depositing their contents an ocean away from where they spun up.
Published In SCIENCE Online June 26 2014 Science DOI: 10.1126/science.1252418
Oceanic Mass Transport by Mesoscale Eddies
Zhengguang Zhang1, Wei Wang1,*, Bo Qiu2