Oceanography's New Catch: Roving Blobs

 The latest beasts discovered in the Atlantic won't munch unwary swimmers or swallow luxury liners, but they may wreak havoc on French farmers and other landlubbers across Europe. The newfound creatures are an oceanographic phenomenon--giant patches of warm or cold water that drift slowly around the North Atlantic and may alter European weather.

 Two Florida researchers identified these climatic critters by studying sea surface temperature records from 1948 through 1992. During that period, 14 of these temperature anomalies developed and roved the ocean basin, report Donald V. Hansen of the University of Miami and Hugo F. Bezdek of the National Oceanic and Atmospheric Administration in Miami. They describe their work in the April 15 Journal of Geophysical Research.

"I think this is a seminal paper," comments oceanographer James J. O'Brien of Florida State University in Tallahassee. "They have identified a very important mode of ocean variability."

 Hansen and Bezdek found that the large warm and cold blobs measured hundreds or thousands of kilometers across and typically had a lifetime of 3 to 10 years. Although the vertical thickness of these patches remains unknown, measurements made by ships passing through them suggest that they may reach depths of 400 meters.

 As they drifted, the temperature anomalies followed the path of prevailing ocean currents, but they moved at only one-third to one-half the speed of the actual currents--an observation that scientists cannot yet explain.

 The newly described phenomenon lasts much longer than the well-known El Nino warmings in the tropical Pacific Ocean, which usually persist for a year or two. Although Hansen and Bezdek focused on the North Atlantic, they suspect that long-lived temperature anomalies are also drifting around other ocean basins.

 Previously, oceanographers believed that temperature anomalies were stationary. In the 1960s, the late Norwegian meteorologist Jacob Bjerknes found hints of traveling temperature anomalies in the Atlantic, and other researchers later detected similar isolated examples. But oceanographers did not pursue these sporadic sightings, says Yochanan Kushnir, a meteorologist at the Lamont-Doherty Earth Observatory in Palisades, N.Y.

 Hansen and Bezdek identified five cold and nine warm patches moving around the Atlantic by making maps of January ocean temperatures that strayed furthest from average conditions. Their maps show blobs slinking across the ocean like amoebas on a microscope slide.

 In one example, a cold patch developed off the coast of Florida in 1968 and started drifting eastward. By 1971, the anomaly had greatly elongated and hit the coast of Africa. It then turned south and traveled westward across the tropical Atlantic until it reached the coast of South America in 1975. Over the next 2 years, the cold region withered and finally disappeared.

 Because sea surface temperatures strongly influence weather and climate, the researchers suspect that these long-lived Atlantic anomalies affect conditions in Europe and perhaps elsewhere. For instance, the researchers suggest that a warm patch in the late 1950s helped cause a prolonged Scandinavian drought. Oceanographers cannot explain how these anomalies form or what drives them, but similar features appear in some computer simulations of ocean temperatures. By dissecting the computer versions, researchers hope to learn more about these wandering weather makers of the Atlantic.