The oceans seem to be warming up not as "greenhouse" theories predict but as if they were in a giant microwave oven, with waters midway between the surface and floor gaining heat fastest, scientists reported Wednesday.

Britain's James Rennell Center for Ocean Circulation concluded this from a deep-ocean hydrographic section taken along the route Columbus sailed 502 years ago at a latitude of 24 degrees North, roughly from West Africa to Florida."By comparing these with the results of two previous surveys at the same latitude, they show that the temperature of this part of the North Atlantic has been rising steadily since 1957, possibly because of the increasing quantities of carbon dioxide in the atmosphere," they wrote in the science journal Nature.

Harry Bryden, from the research center in Southampton, said that between 1957 and 1992 the temperature of the ocean about 3,500 feet down rose by 0.6 F to 40.1 F. Conventional models of climate change have assumed that the seas were warming up fastest on the surface.