Lots of oceanographers think about how our churning oceans decide the distribution of sea life. You can see the effects even from space, as tie-dye streaks of bright plankton mark eddies and current boundaries.
But a few scientists have their thinking caps on backwards, and they’ve made a phenomenal discovery: Sea life, it seems, can toss the oceans around. John Dower and Eric Kunze report in this week’s Science that tiny, shrimplike krill may supply as much as a third of the energy that mixes ocean waters.
Their brawn is rooted in prudence. Krill are pretty low in the food chain – snack food and staple to everything from blue whales to jackass penguins. They stay alive by cowering in the gray depths, fasting all day a hundred meters down. At nightfall, they swim to the surface en masse and start slurping down phytoplankton in the dark.
It’s these mass movements that get the water moving. With literally millions of them moving in the same direction all at once, a trail of water jets downward behind them.
Dower and Kunze actually measured the resulting turbulence by lowering a very small, uh, turbulence-measurer into Saanich Inlet, near Victoria, British Columbia. When the krill were on the move, turbulence values shot up by three to four orders of magnitude.
The scientists took these values and calculated the amount of mixing energy the krill must have been producing. Then, using estimates of krill numbers in the global ocean, they extrapolated from their inlet to take a guess at the total mixing power krill are capable of.
(This kind of extrapolating to the entire rest of the planet is the sort of basic mistake in both logic and optimism that all scientists are supposed to have beaten out of them in graduate school … the only exception being if they’re writing for Science at which point it’s sort of customary to go for broke.)
It is kind of fun, isn’t it? Thinking of those great columns of krill floating skyward like feathers in the world’s biggest pillowfight? And pumping out, or so it has been estimated, 1 terawatt of power. In simpler terms, that’s one million kilowatts, or nearly the power output on the smile of a successful politician.
The staggering importance of keeping the oceans well stirred is a truth I was late in appreciating. But it’s striking when you think of it, only slightly simplistically, this way: All the light is at the top of the ocean and all the nutrients are at the bottom. If you can’t get the two together, no photosynthesis.
But wait, there’s more. The 1.2 billion cubic kilometers of water in the ocean can store a lot of heat and absorb a lot of carbon dioxide…but only if the water periodically comes to the surface and then sinks under again. It appears that we owe at least a third of our thanks to some salty, boneless, very-hard-to-see, backwards lemmings.
Other media interest in the story: Scientific American plays up the power angle; National Geographic points out krill’s role in bringing up nutrients; New Scientist goes one step beyond everyone else and suggests krill may be helping control climate change (by stimulating phytoplankton growth, thereby pulling carbon dioxide out of the atmosphere). Interestingly, here’s a blog debate about whether New Scientist are too sensational for their own good, at least when it comes to physics. MSNBC gets a piece of all these angles, but then tragically confuses krill and anchovies in the very last sentence.
As for me, I’m just interested in what my friend the turbulentologist Tetjana Ross has to say about the whole thing.