Different mechanisms of heat transfer to the ocean surface dominate within different depth regions. Under suitable weather conditions, radiation dominates within the upper micron of depth. Turbulence is dominant at greater depths, but the evidence indicates that, with wind speeds less than 10 m/sec, it dominates only at depths greater than 0.5 mm. A region in which heat is transferred almost entirely by conduction lies between. Radiometric measurements of the total heat flow to the ocean surface may be made in this region.