SCIENCE

Notebook

Quick Like a Glacier

Two of Greenland's largest glaciers that flow to lower elevations and the ocean are waxing and waning rapidly, researchers reported last week, suggesting that the effects of global warming on sea levels may be difficult to predict.

The study -- based on satellite data and conducted by scientists at the University of Washington and the University of Colorado -- found great fluctuations in the rate of ice discharge and mass loss from the two glaciers. The glaciers' rate of mass loss doubled in less than a year in 2004 but then dropped in 2006 to close to previous rates.

"The synchronous and multi-regional scale of this change, and the recent change in Arctic air and ocean temperatures, suggest that these changes are due to climate warming," wrote the authors, led by Ian M. Howat, a research associate at the University of Washington's Polar Ice Center. "The possibility that ice dynamics are so highly sensitive to climate change is of concern, because the physical processes that would drive such a relationship . . . are not realistically included in ice sheet models used to predict rates of sea-level rise."

The researchers wrote in last week's issue of Science that while it is difficult to predict how the glaciers will fluctuate in the future, "continued warming may cause a long-term drawdown of the ice sheet through a series of such discharge anomalies, perhaps with a similar degree of variability."

-- Juliet Eilperin

Antennae and Stability

Scientists have long known that insects' antennae perform various sensory functions. Cut them off, for example, and males lose the scent of that female they were chasing.

Now researchers have found that in some insects, at least, antennae are also breeze detectors that tell an insect whether it is being buffeted off course and help it correct for crosswinds and downdrafts.

The discovery has its roots in the 1940s, when scientists discovered the function of "halteres" -- club-shaped organs that substitute for the rear two wings on some insects such as flies. Halteres vibrate in sync with the front wings and are sensitive to small changes in air flow. As they bend with tiny air currents, they tell a fly about changes in its body's pitch, roll and yaw -- the three ways a flying object can veer from its intended orientation.

But how do four-winged insects stay oriented, since they lack halteres? Some, such as dragonflies, use vision. But moths and other insects fly at night, when light levels are too low to rely on vision alone to, say, hover precisely over a flower in a crosswind.

Now Sanjay P. Sane of the University of Washington and his colleagues have found that antennae, like halteres, vibrate during flight and that tiny hairs at the base of those appendages detect the subtle vibratory changes that occur when an insect veers off its intended axis. In experiments with the hawk moth, Manduca sexta, the team used high-speed video cameras to document the vibratory patterns; tested nerve signals to see how air movement information is conveyed to the brain; and showed by removing and then re-attaching antennae that they are key to stable flight.