SCIENCE NOTEBOOK

Monday, February 11, 2008

Motorless Sub Keeps Going

Scientists seeking to gather temperature, salinity and other data from the oceans have long had two choices: steam out to sea on expensive research ships or launch unmanned submersibles whose batteries typically die in a few days.

Now engineers and oceanographers have successfully tested a novel unmanned mini-sub that grabs energy from temperature differences in the ocean. In an ongoing test, the "thermal glider" has been traveling, without a propeller, for nearly two months.

"We now believe the technology is stable enough to be used for science. It is no longer just a prototype," said Dave Fratantoni of the Woods Hole Oceanographic Institution on Cape Cod.

Made by Webb Research Corp. of Falmouth, Mass., the glider changes its buoyancy by pumping fluid back and forth between bladders inside and outside its hull. Near the surface, where waters are relatively warm, wax within a chamber melts and expands, producing a pumplike force that can push water between bladders. To ascend from frigid depths, fluid is pumped from an inner bladder to one outside. The vessel's mass does not change, but its volume increases, increasing buoyancy. Back at the surface, pumps are recharged as wax melts and expands anew, even as fluid is drawn again to the inner bladder, reducing volume and slowly sinking the vessel again.

Fixed fins convert the rising and falling into forward momentum, just as a paper airplane's wings make it glide forward when dropped.

The six-foot craft travels about 1 mph, repeatedly bobbing up and then sinking to 4,000 feet as it goes, fueled by a temperature differential of about 43 degrees Fahrenheit. Instruments that can run on batteries for months gather data from the ocean and transmit to satellites with each surfacing.

One goal is to study climate change. And because the glider has no motor, Fratantoni said, it is ideal for underwater acoustic studies.

-- Rick Weiss

Bollworm Evolves to Resist Toxin

In the last decade, dozens of varieties of corn, soybeans and cotton have been planted that were genetically modified to produce a bacterial protein, called Bt, that kills insect pests. Now a strain of bollworm, an insect that voraciously attacks cotton plants, has evolved that is resistant to the genetically modified plants that are supposed to kill it.

The newly resistant bollworms arose in a dozen crop fields in Mississippi and Arkansas between 2003 and 2006. They are the first pests known to have become fully resistant to the modified plants.

"What we're seeing is evolution in action," said lead researcher Bruce Tabashnik of the University of Arizona, who reported the finding in the February issue of the journal Nature Biotechnology.

The issue of resistance to genetically modified plants has long been contentious because organic farmers also use the Bt toxin, made by the widespread bacterium Bacillus thuringiensis (hence the name Bt), to control pests. They feared that use of Bt in genetically engineered crops would lead to development of Bt resistance, making the natural pesticide gradually less effective.

To delay that process, non-Bt crops are generally planted near Bt-modified crops to provide "refuges" -- areas where there are no resistant insects because Bt is not being used. That technique results in resistant insects mating with nonresistant ones, which generally produces nonresistant offspring. Bollworms are apparently unique, however, in being able to pass on Bt resistance to offspring when one resistant insect mates with a nonresistant one. The University of Arizona study concluded that bollworm resistance to Bt cotton evolved fastest in places with the fewest refuges.

-- Marc Kaufman

'Thermostat' May Protect Coral

Some coral reefs in naturally warm waters near Australia appear to be relatively unaffected by the kind of climate-change-induced "coral bleaching" that has damaged reefs in regions where water temperatures have risen more dramatically, scientists have found.

The findings, published in the online journal Geophysical Research Letters, appear to support a theory that a natural "ocean thermostat" prevents surface water temperatures from climbing above 88 degrees Fahrenheit in open oceans, the researchers said.

Scientists from the National Center for Atmospheric Research in Colorado and the Australian Institute of Marine Science studied the correlation between sea temperatures and bleaching -- a whitening caused by a loss of algae -- by analyzing sea-surface temperatures from 1950 to 2006 in tropical waters. They documented relatively few episodes of coral bleaching in the Western Pacific Warm Pool, an area northeast of Australia where the temperature of the naturally warm waters has risen little in recent decades.

They concluded that reefs that have evolved in naturally warm waters may enjoy a degree of protection from global warming by the "ocean thermostat," while reefs in cooler waters do not.

"Global warming is damaging many corals, but it appears to be bypassing certain reefs that support some of the greatest diversity of life on the planet," said lead researcher Joan Kleypas. "In essence, reefs that are already in hot water may be more protected from warming than reefs that are not. This is some rare hopeful news for these important ecosystems."

-- Christopher Lee