Low values of oceanic heat flow

A puzzling feature of the measurements of heat flow at sea is the occurrence of values lower than 0.4 μcal/cm2 sec. There are no counterparts of these low values among the continental measurements, though low or even negative values could be obtained if the thermal gradients in the uppermost 100 meters, or so, were accepted as representative. These negative values are commonly disregarded in favor of the regular positive values found at greater depths. In many of the oceanic measurements, the penetration does not exceed a few meters, and it is necessary to consider carefully any factors that might influence the gradients at such shallow depths if we are to distinguish real differences of heat flow.