Geologists take magnetic view through ice.

Scientists have a new tool for analyzing geologic features hidden beneath thousands of meters of Antarctic ice and under the storm-tossed seas around the continent.

At last week's meeting in Boston of the American Geophysical Union, an international team unveiled a map of the minuscule magnetic variations in Antarctica and the seafloor surrounding it. The new map results from a 6-year research saga dubbed the Antarctic Digital Magnetic Anomaly Project. The compilation includes data from surveys conducted by eight countries since 1957. This is the first all-encompassing image of Antarctica's magnetic anomalies, says team member Ralph R.B. von Frese, a geophysicist at Ohio State University in Columbus.

Antarctica is the last great unexplored landmass on Earth. It's about twice the size of the lower 48 U.S. states, and more than 99 percent of it is covered by ice sheets up to 4 kilometers thick. Although some types of radar can discern the shape of the terrain beneath the ice, none can determine the mineral content of the rocks that lie there. Magnetic measurements, however, can help scientists make such identifications.

The project team collected data that other researchers obtained using instruments on ships and small aircraft. In this image of Earth's magnetic field south of 60 [degrees] S, the strongest anomalies are in red (positive) and violet (negative). The outline of Antarctica is in white.

However, those surveys provided high resolution measurements for less than half the continent. The team filled in large gaps, most of them in the continent's vast interior, with satellite data. Other challenges included assimilating data from a variety of formats--including paper records from older surveys--and compensating for subtle changes over the years in Earth's overall magnetic field.

"These magnetic anomalies are like a tape recording of Earth's history," notes von Frese. "The trick is to figure out how to read it."

For example, he says, scientists now can combine the new map with images produced by ice-penetrating radar. That could help identify rifts, volcanoes, and other geologic features hidden far below the Antarctic ice, says von Frese.

With the map, scientists can now quickly determine which Antarctic areas have been surveyed in detail, says Patrick T. Taylor, a geomagnetist at NASA's Goddard Space Flight Center in Greenbelt, Md. That should help them minimize future duplication of effort.

A high-resolution print version of the map will be available to scientists late this summer, says von Frese. Along with the reams of raw data collected during the surveys, the map will be published on a compact disk next year.