Isaacs—Faughn-Schick—Sargent: Deep-Sea Moorings 275 
mid-latitudes. Statistical formation for many areas is given in the Atlas of 
Surface Currents (USN HO, 1944-1947). The depth of the mixed layer in the 
tropics and at mid-latitudes in summer may be obtained directly with a bathy- 
thermograph. Statistical information for middle and high latitudes in winter is 
searce. In our experience moorings on isolated sea mounts (at about 700 fathoms) 
are much less satisfactory than moorings over the adjacent deep sea floor at 2,500 
fathoms. In the Marshall Islands, at least, currents over deep sea mounts seem 
to be intensified. 
The indicated surface current often reaches to the bottom of the mixed layer. 
Seattered observations indicate that currents below the mixed layer seldom exceed 
0.5 knot. Observations at the bottom of the sea in deep water indicate that currents 
very seldom exceed 0.2 knot. At the Scripps Institution, when direct observations 
of current velocities below the surface are lacking, a rule of thumb is used in 
assuming the current profile below the mixed layer. This rule states that at the 
depth of temperature transition the current is assumed to be 0.5 knot, and, at the 
bottom, 0.2 knot. Direct observation or statistical information shows that below 
the mixed layer the temperature decreases rapidly with increasing depth in a 
relatively shallow zone, and then very slowly the remainder of the way to the 
bottom. Usually visual inspection of a vertical temperature profile is sufficient to 
identify the approximate depth at which the transition occurs. In the absence of 
a temperature profile, the depth of transition may be assumed to be 200 feet below 
the bottom of the mixed layer. The complete velocity profile assumed is shown in 
figure 2. 
Obviously a measured current profile is preferable, but this ordinarily is not 
Surface 
Bottom of Mixed Layer 
Depth of Transition 
Depth 
Bottom 
0.2 05 
Velocity (knots) 
Fig. 2. Assumed current profile. 
