SECT. 5] SEASONAL CHANGES IN SEA-LEVEL 493 



in these areas. The other principal areas of discrepancy in the Pacific Ocean are 

 interesting in that they occur just where recorded deviations in sea-level have 

 been noted to be large — especially along northeastern Australia and Mexico. 

 Both of these are tropical to subtropical coastlines and, at least along sections 

 of the shoreline, have shallow water offshore. The evidence suggests that, in 

 these areas, non-isostatic effects related to phenomena (d) or (e) may be of 

 considerable magnitude. 



Oceans other than the Pacific have not yet been adequately analyzed for the 

 isostatic term, although a little work on steric levels in some areas, and con- 

 siderable work on pressure effects in others, has been done. At least part 

 of the very large deviations observed in the northern Indian Ocean are steric 

 in behavior, since changes in specific volume related to changes in salinity are 

 large (LaFond and Rao, 1954). This is the only relatively open area identified 

 to date where salinity changes are the predominant factor in a large steric 

 term. It seems reasonable to conclude that the real cause here is the monsoon, 

 and that the active agents are the precipitation that falls during the period of 

 onshore winds and the monsoon winds themselves. However, a complete 

 quantitative explanation has not yet been given. 



A number of studies have been published where other effects in addition to 

 changes in pressure and volume have been considered for a particular area. A 

 complete list would require a very long bibliography ; a few typical examples 

 are given here. The large and complicated variations in Indonesian waters 

 have been studied in detail by Wyrtki (in press) and he relates them almost 

 entirely to changes induced by the monsoon. In this area this involves not only 

 onshore and offshore wind stress and changes in precipitation and evaporation, 

 but also all of the complications of varying currents carrying different water- 

 masses through restricted passages into semi-enclosed, shallow basins. Barber 

 (1957) found that recorded sea-levels at Prince Rupert, British Columbia, 

 Canada, corresponded well to near-shore variations in isostatic levels, and he 

 was, moreover, able to attribute the changes in water volume at that locality 

 to variations in water-mass induced by the seasonally varying winds. Here the 

 term water-mass is used in the customary way to indicate the types of water in 

 the column, after the definition of Helland-Hansen (1916). Balay (1958) has 

 studied the seasonal variations in level along Argentina. He notes that the 

 recorded variations are quite similar for long distances along this coast, although 

 all of the associated phenomena vary considerably with latitude. He has found 

 that the third harmonic of the annual variation is consistently present, with an 

 amplitude of 2.5 cm, and attributes this to the influence of the continental 

 shelf on the combination of the annual and semi-annual wave. Chase (1952) 

 has continued the work along the southeastern coast of the United States. He 

 finds a high correlation between seasonal variation in sea slope between Charles- 

 ton and Bermuda (and hence in sea-level at the gauges) and the strength of the 

 winds in the North Atlantic gyre. A major part of the work on particular areas, 

 however, continues to emanate from the countries of northern Europe. Lisitzin, 

 in particular, has made a number of studies, principally in sections of the 



