I. SEA LEVEL - - AN ABBREVIATED SUMMARY 



The sea surface rises and falls in time intervals of less than a tenth of a 

 second (in the case of capillary waves) to geological ages, and in height from less 

 than a millimeter to over a hundred meters. A plot of yearly mean sea-level ele- 

 vation against time, using Atlantic City, New Jersey, as an example, reveals yearly 

 variability, tendencies of change from several years to about two decades, partially 

 hidden periodicities, and an apparent secular trend (figure 1), The term "secular," 

 in this case, means nonperiodic. The word "apparent" is used since it is not known 

 whether the trend is truly nonperiodic or merely a segment of a very much longer 

 oscillation. 



Yearly variability is due to variations in the meteorological and oceanographic 

 parameters of wind (Roden, 1960), direct atmospheric pressure (Roden, 1960, 1966), 

 precipitation, river discharge (Meade and Emery, 1971), currents (Garrett and 

 Petrie, 1981), evaporation, salinity, and water temperature (Stewart et al . , 1958; 

 Roden, 1960, 1966). Wind stress accounts for both setup and net wave transport as 

 well as for causing and altering many currents. Direct atmospheric pressure alters 

 sea level by the inverted barometer effect. Precipitation and river discharge 

 decrease salinity and thus density, allowing higher sea-level stands. Likewise, 

 evaporation increases salinity and thus increases density giving lower sea levels. 

 Changes in water temperature also change the density with the appropriate response 

 in sea level. Variations in currents that approach (to any degree) a geostrophic 

 balance will have their athwart-current slopes altered, which register as sea-level 

 changes. The above parameters are interactive, of course. For example, anything 

 (such as density differences) that would help to maintain sea-level differences 

 across a current (which approaches a geostrophic balance) is maintaining the 

 current's slope and thus the current. By the same token, the current maintains the 

 slope (sea-level difference), contributing to the density difference on each side. 



Tendencies are attributed to climatological changes in the above parameters. 

 The partially hidden periodicities are due to such phenomenon as the lunar node 

 cycle (Rossiter, 1967) and the Southern Oscillation (Fairbridge and Krebs, 1962), et 

 cetera. The apparent secular trend results from the effects of glacial-eustacy, 

 thermal volumetric changes, vertical land movements, and both climatologic and 

 oceanographic apparent secular trends. 



