On the horizon: news from the frontiers of science

Arctic ice shrinks to a new low, saber-toothed cat's growl was worse than its bite, ancient woodworking tool hints at global trade routes.

Arctic ice shrinks to new lows

For those who track the ebbs and flows of the Arctic's icecap, the summer of 2007 was a record-breaker – the smallest expanse of summertime ice since satellites began measuring it in 1979.

Indeed, since '79, the rate of decline in September's sea ice has averaged about 72,000 square miles a year, according to data released this week by the National Snow and Ice Data Center in Boulder, Colo. One reason: less multiyear ice carried over from previous seasons. Younger ice fails to grow thick enough to survive the summer melt season.

A separate study published this week by a team of researchers from the National Aeronautics and Space Administration, the University of Washington, the US Army Corps of Engineers, and the National Ice Center in Maryland shows that this perennial ice shrank by 23 percent, or 420,000 square miles, between March 2005 and March 2007. Unusually strong wind patterns in the region drove ice out into the Atlantic "like a runaway train," the team explains. This set the stage for the record low levels of summer sea ice in 2005 and 2007. The work appears in the current issue of Geophysical Research Letters.

"While a number of natural factors have certainly contributed to the overall decline … the effects of greenhouse warming are coming through loud and clear," notes Mark Serreze, a senior scientist at the Snow and Ice Data Center.

Ancient cat: big teeth, weak bite

The sharp, curved fangs of the saber-toothed cat leave no doubt that, as a hunter, this critter meant business. Now, a team of scientists in Australia has found that the cat's growl may have been worse than its bite. Indeed, modern lions munch with about three times as much force as the older cats, known as Smilodons.

"For all its reputation, Smilodon had a wimpy bite," notes Steven Wroe, a paleontologist at the University of New South Wales in Sydney who took part in the research.

For 150 years, paleontologists have argued over how the cat used its fangs and how much crunching force its jaws could apply. Dr. Wroe and a colleague at the University of Newcastle used a computer-based approach to reverse-engineer the animal's jaws and teeth and estimate the forces Smilodon's eating machinery could endure.

For the most part, Smilodon's munch fell short of today's lions of similar sizes. Yet the duo notes that its powerful body was well adapted to wrestling larger animals to the ground. Then an appropriate chomp would dispatch the prey. The results of the study appear in the current issue of the Proceedings of the National Academy of Science.

Old tool hints at ocean trade routes

Imagine an ax head turned sideways at the end of a handle, and you have a good picture of an adze – a woodworking tool used to shape logs. In ancient Polynesia, adze heads were made of volcanic stone. And therein lie clues to trade routes among the string of islands in the South Pacific.

A pair of scientists from Australia says it has found a geochemical "smoking gun" for interisland trade that began sometime before AD 1200 and ended around 1450 – carried by large sail-bearing canoes over routes spanning at least 2,500 miles.

The adze heads, found on tiny islands in the Tuamotu Archipelago – south of the Marquesas Islands – carry chemical fingerprints unique to the volcanoes that formed the rock from which they were made. By comparing the adzes' chemistry with that of volcanic rock from a range of islands in the area, they found that the tools came from as far away as the Hawaiian Islands.

The results confirm oral histories, experimental voyages attempting to retrace the routes, and other lines of evidence that argue for widespread trade among the far-flung Polynesians. The study appears in the current issue of the journal Science.

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