3. The patterns and magnitudes of circulation of the oceans 
themselves. For deep and shallow waters it would be necessary to 
know the rates of movement, overturn and mixing to predict the fate 
(10) 
of any disposed material. 
Stability and Circulation of the Oceans. 
The ocean is essentially a film of water on the surface of 
the earth; the vertical dimension is about one one-thousandth of 
the horizontal dimension. Most of the mixing that occurs in the 
ocean is not vertical but horizontal; this results from dimensional 
differences and from vertical density gradients. Convective overturn 
is an exceptional = 
It was previously thought that the wind moved most of the 
ocean's waters. This appeared obvious. However, if there were no 
wind at all, the oceans would still circulate in much the same way 
as they do at present. 
In each of the oceans there is a lens shaped layer of water 
with a relatively high vertical temperature gradient which lies 
deepest in mid latitudes, i.e. the surface layer is separated from 
deep water by this thermocline layer which happens to be thickest 
in mid latitudes and thinner near the equator, It outcrops at 
about 50° to 55° latitude in all the oceans; see Fig. A. In the 
southern hemisphere oceans there is apparently a good dealof sinking 
along surfaces of constant density into this "thermocline" layer 
because the water can be traced from the surface in high southern 
latitudes all the way to the equator. In the Atlantic the water 
=54~ 
