DEEP-SEA TIDES 



Walter H. Munk 



University of California 

 San Diego i California 



ABSTRACT 



The classical Laplace tidal theory, when applied in 

 numerical form to the world's ocean basins, does not 

 yield results in good accord with observations. In 

 part, this may be due to density stratification and in- 

 ternal tides (coupled to external tides); and in part to 

 dissipation at the ocean boundaries. At a given port 

 the spectrum of the observed tides shows a complicated 

 line structure superimposed over a continuum. The 

 continuum rises at the frequencies where the lines are 

 clustered, probably as a result of internal tides. 



Tide dissipation leads to an exchange of angular mo- 

 mentum between the spin of the earth and the orbit of 

 the moon. As a result of this spin-orbital coupling, 

 the length of day and month are both increasing. Ob- 

 servations of the moon since 1680, of Babylonian 

 eclipses and of the structure of Devonian tropical coral 

 (which give the number of Devonian days per year) 

 confirm these calculations. 



To untangle these problems, it is probably necessary 

 to make observations in the deep sea, relatively re- 

 moved from the scattering and absorbing boundaries. 

 Such observations have now been made for the last three 

 years , and they yield relatively clear pictures of the 

 deep-sea tidal pattern. The tides in the northeast 

 Pacific can be roughly accounted for by superposition 

 of a northward-traveling Kelvin wave (trapped by 

 rotation to the boundary) and a southward- traveling non- 

 trapped Poincar^ wave. 



In order for the calculations to be realistic, they need 

 take into account the tidal yielding of the sea floor. 



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