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Last Updated: Wednesday, 13 December 2006, 13:19 GMT
Sea creatures' global warming fix
By Molly Bentley
San Francisco

Salps occur in great swarms

A simple sea creature could help to address the problem of global warming, a scientist claims.

Tiny tube-like salps mop up greenhouse gases by feasting on carbon-dioxide soaked algae from the oceans.

The US researcher told an American Geophysical Union meeting of his plans to adjust nutrient levels in the ocean to boost the sea animal's populations.

But other scientists warned of the unknown consequences of meddling with the ocean's complex ecosystem.

Excreting carbon

The salp is a transparent hollow tube, no bigger than an unshelled peanut, that swims around vacuuming up microscopic plants.

Because it is efficient in sucking up marine algae that have absorbed dissolved carbon dioxide (CO2), the salp is seen by one scientist as the key to sequestering excess atmospheric gas to the ocean bottom.

"It's just a feeding tube," said Phil Kithil, CEO of Atmocean Inc, a private research firm in Santa Fe, New Mexico. "It eats at one end and excretes at the other."

The solid carbon pellet that emerges from the salp sinks and dissolves deep enough in the ocean to be effectively taken out of the carbon cycle.

Faecal pellets (Madin/WHOI)
Salp pellets take carbon down into the deep ocean

Mr Kithil wants to increase the algae-eating salp population in the world's oceans by boosting its food supply.

He proposes to bring deep-water nutrients to the surface with arrays of wave-activated pumps.

With an infusion of nutrients, the algae bloom would mushroom, according to the untested proposal, and absorb mass quantities of dissolved CO2, before being eaten and excreted by salps.

The speculative idea includes releasing thousands of coiled pumps that un-spool when they hit water, extending like organ pipes.

Each pump consists of a flexible tube, up to 1,000m in length, which would draw cold, nutrient-rich water to the ocean surface.

Mr Kithil estimates 1,340 pump arrays, each consisting of 100,000 tethered pumps over 100,000 sq km, could sequester nearly a third of manmade CO2 annually.

So far, the pumps have only been tested for proof of concept.

Next summer, in an experiment with 25 pumps off the coast of Bermuda, Mr Kithil will see whether he can actually increase algal blooms and lure salps to feed.

Mr Kithil's idea falls under the umbrella of geoengineering - a diverse and growing collection of proposals, mostly untested, to employ large-scale engineering solutions to the planet in an attempt to restore its energy balance.

Artist's impression of space shade.  Image: Science Picture Library
Geoengineering considers big solutions to a big problem

But some climate scientists warn the possible side-effects of tinkering with the Earth's climate do not justify the risk.

"The ocean is such an alien system for us to be tinkering with based on the current level of science," said Jim Bishop, a bio-geochemist at Lawrence Berkeley National Laboratory.

"We don't understand the ecosystem dynamics well enough to predict what will happen.

Biologist Larry Madin at Woods Hole Oceanographic Institution has previously highlighted salps' CO2 mopping abilities.

But as a cure for global warming, "it's just not that simple," he told the BBC.

"You can't count on the fact that these organisms will show up."

Salps grow in some places and not in others, Dr Madin explained.

"It's easy enough to add nutrients and make things grow faster," he said, "but the next step is harder - to try controlling what happens to larger more complex animals with more complicated life cycles."

Mr Kithil presented his work at the American Geophysical Union Fall Meeting here in San Francisco.

Pump graphic
1. Buoy: Helps hold the pump in position
2. Pump: The tube is 1.5m wide and 1,000m long. The great length helps it reach cold water
3. Valve: Water is drawn through the open valve on wave down slopes, no external power needed
4. Cold water: On wave up slopes, cool water spills out of the pump
5. Pump sites: Locations can also be chosen to reduce hurricane risk by cooling surface waters

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