Progress report on scattering layer observations in the Atlantic Ocean

Observations with a Fathometer have shown the wide occurrence of a layer of scatterers of supersonic sound in the daytime in the Atlantic Ocean and the Gulf of Mexico at a depth of 150–250 fathoms. Other subsidiary layers are also recorded. The main layer exhibits diurnal migration in depth whose similarity to the behavior of plankton suggests a planktonic control. The behavior of the layer under various conditions, alternative hypotheses on the nature of the scatterers, and preliminary experiments to test the theory of planktonlc control are discussed.