Temperatures on the rise in deep Atlantic.

While retracing Columbus' route across the Atlantic, an international group of scientists detected a substantial warming in the subtropical part of that ocean. Water temperatures at some depths have increased by as much as 0.32 [degrees] C since the late 1950s, a finding roughly in keeping with predictions about global green-house warming, according to the research team.

"That's a huge signature and certainly warrants further monitoring," says one of the project participants, Robert Millard of the Woods Hole (Mass.) Oceanographic Institution. Gregorio Parrilla of the Spanish Oceanographic Institute in Madrid served as chief scientist on the cruise. The investigators report their findings in the May 5 NATURE.

Sailing on a Spanish naval ship in the summer of 1992, the oceanographers followed the latitude line of 24 [degrees] N, taking measurements every 60 kilometers. Other teams had traveled the same route in 1957 and in 1981.

During the 1981 expedition, researchers discovered that the western portion of the Atlantic had warmed by as much as several tenths of a degree Celsius since 1957. Between 1981 and 1992, however, the central and eastern parts of the ocean warmed and the western third cooled slightly. Over the full 35-year period, temperatures increased across the entire 24 [degrees] N band of the Atlantic. Most of the warming was concentrated between the depths of 700 and 2,500 meters.

The oceanic warming generally resembles the pattern expected to develop as a result of increased greenhouse gases in the atmosphere. But the two do not match exactly. Although computer models suggest that temperatures in the surface waters should increase the most, actual observations show a combination of warming and cooling there.

Ronald J. Stouffer of the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory in Princeton, N.J., says measurement differences may account for the lack of pronounced surface warming. The three expeditions traveled at different times of year, and the temperature at the top of the ocean varies dramatically from season to season.

Stouffer and others note that natural climatic variations could have caused some or all of the ocean warming. Then again, greenhouse gases could be the culprit. For now, scientists can't apportion the blame.