On the edge between water and ice.

On the edge between water and ice

In a project involving 11 nations, sevenships, eight aircraft, four helicopters and more than 200 people, oceanographers have journeyed to the Fram Strait region of the Greenland Sea to study the marginal ice zone--the boundary between open and ice-covered ocean.

With the seasonal advance and retreatof polar ice, roughly 7 percent of the world ocean is at some time during the year part of this boundary zone. The Marginal Ice Zone Experiment, called MIZEX, is helping scientists develop a comprehensive picture of the physical and biological interactions between ice, ocean and atmosphere at this boundary.

The Fram Strait area is of particularinterest because it is the "main [ice] outlet for the Arctic Sea,' says Miles McPhee, who served as chief scientist on the research vessel Polarqueen for the 1984 leg of MIZEX. In the April 24 SCIENCE, five groups report on their findings from MIZEX-84.

This area, the northernmost extensionof the Gulf Stream, is the mixing ground of cold, low-salinity Arctic water and warmer Atlantic water. Knowledge gained from MIZEX will have applications in the study of global climate. "It's a fairly strong feeling,' says McPhee, "that sea-ice is a very sensitive indicator of what the climate is doing.' Even small changes in the global climate, such as a "greenhouse' warming trend, will noticeably affect the position of the marginal ice zone, says McPhee.

MIZEX scientists conducted the mainresearch during the summers of 1983 and 1984 and followed that with a winter study this March. Led by Norwegian oceanographer Ola Johannessen of the University of Bergen, these three segments were centered on the prime meridian, 400 kilometers east of Greenland.

One of the important results of MIZEXwas that it demonstrated the potential value of remote sensing, says Robert Shuchman of the Environmental Research institute of Michigan, in Ann Arbor. Because marginal ice zones are located in polar areas that are dark for half the year and are often obscured by clouds, MIZEX relied on a microwave radar, called synthetic aperture radar (SAR), mounted on aircraft to provide images with up to 15-foot resolution.

"Without SAR to give us insight into thecirculation patterns, I don't think one can study places like the Greenland Sea,' says Shuchman, who has just returned from the Fram Strait.

Shuchman and his colleagues reportthat SAR helped them located the position of transient eddies near the ice edge. By analyzing sequential SAR images, the group was also able to locate an eddy beneath the unbroken interior ice. Eddies, which circulate water at the edge of and under the ice, play a key role in determining how quickly the interior ice melts and breaks into smaller pieces.

In a separate study, MIZEX biologiststested to determine how eddies affect the populations of phytoplanktons, one-celled ocean organisms that serve as the basis of the polar food web. Walker Smith from the University of Tennessee in Knoxville told SCIENCE NEWS that "eddies were acting as a pump in the circulation so that nitrate [an essential nutrient] was being injected into the surface, therefore stimulating biological productivity.'

More detailed results of MIZEX willappear in an upcoming special issue of the JOURNAL OF GEOPHYSICAL RESEARCH dedicated to studies of marginal ice zones.

Photo: A SAR image from MIZEX-84 with acentral eddy approximately 30 kilometers in diameter. Bright Zones are ice; dark zones are ice-free water.