494 PATTULLO [CHAP. 22 



Baltic Sea, and has pointed out that in this area water supply, wind stress, 

 currents and sea-ice must all be considered (Lisitzin, 1946, 1957). 



4. Summary 



We have in this discussion considered the changes in sea-level from season to 

 season ; let us now summarize them by area. 



A. Subtropics 



In subtropical latitudes, extreme deviations from the annual mean occur 

 near the times of the equinoxes. Levels are high north of the equator in Sep- 

 tember and south of the equator in March and vice versa ; ranges of 10 to 15 cm 

 are typical. This variation is due principally to seasonal variations in heat 

 storage in the oceans, induced, to a large extent, by the seasonal variations in 

 local heating. 



B. Tropics 



In the tropics, deviations are largest at the times of the solstices, but whether 

 the level is lower or higher than the annual mean depends on the longitude. 

 The central parts of the oceans experience high sea-levels in December, while 

 closer to the coastlines levels are low. In June the deviations are similarly 

 distributed but of opposite sign. As in the subtropics, the deviations at some of 

 the island locations seem related to variations in heat content. However, even 

 in those localities where this relationship is observed, it has not yet been 

 determined whether local heating or advective effects are the predominant 

 influence. 



C. Subarctic 



North of 40°N in the Atlantic and Pacific oceans, subarctic localities have 

 highest levels most frequently in December and January ; the magnitude of the 

 annual range is, again, about 15 cm. These deviations are induced almost 

 completely (except for some local coastal effects) by the seasonal variation in 

 atmospheric pressure. Corresponding variations of opposite sign in other 

 latitudes, which must obviously take place, are not as readily detected because 

 the effect is not concentrated in an equally small area. 



D. Arctic Ocean 



Gauges in the Arctic Ocean all show high levels in September and low levels 

 in March. During December levels are high, except along Alaska. The same 

 pattern, with signs reversed, is observed in June. No observations are available 

 except for the coastal stations, and no explanation of the variations has been 

 given. 



