northward in the Gulf Stream that cannot be found traveling southward 
near the surface. (The Atlantic is essentially closed at the northern 
end.) Therefore, it must come back somewhere underneath. Actually, 
some of it travels southward quite near the surface, in the main 
thermocline, some of it a little deeper, but aap only 
occasionally does it come back via the saab 
If the amount of water that flows into the North Atlantic 
across the equator at the surface (based on dynamic computations) 
is divided into the volume of the North Atlantic, the result is 
a time of circulation of the order of magnitude of 102 years, assum- 
ing that the circulation is perfect, that there are no eddys, dead 
pockets or accelerated ssi sblye ° 
Tracer Dating Techniques to Determine Circulation: The Lamont 
Institute of Oceanography of Columbia University has been working on 
a problem closely related to the circulation of bottom waters. This 
group has been interested in the distribution of sediments on the 
ocean floor and heat flow through these sediments. The cl4 dating 
method which is employed involves collecting a 100 gallon sample of 
bottom water and extracting the carbonate from this at sea. The 
carbonate sample is brought back to shore and a measurement is made 
of its radioactivity. Knowing its activity establishes the age of 
the git and presumably the age of the bottom water from which it was 
taken. Preliminary determinations by this method indicate the age 
of the bottom water to be of the order of magnitude of 10° years. 
The Lamont Institute also has been making tritium assays of 
3 
ocean water. It is anticipated that these H~ measurements will indicate 
how much the annual mixing penetrates to below the seasonal thermocline. 
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