V. OCEANOGRAPHICAL MISCELLANEA 



22 SEASONAL CHANGES IN SEA-LEVEL 



June G. Pattullo 



1. Introduction 



The study of variations in sea-level has a surprisingly long history ; papers on 

 this subject were appearing more than 200 years ago. However, the examina- 

 tion of the seasonal variation requires at least a year's record of reliable observa- 

 tions, all referred to the same fixed point on land. Data for this purpose became 

 adequate earliest in northern Europe but only towards the end of the 19th 

 century. Soon a lively controversy was under way as to the causes of the 

 variations observed, and in 1926 Galle summarized the work of various Euro- 

 pean writers who, in the first decades of this century, had analyzed local data 

 and had advanced hypotheses relating them to meteorological or oceanographic 

 factors. Japanese students were early in the field as well, and were certainly 

 among the first to give their principal attention to the seasonal term (Nagaoka, 

 1908 ; Omari, 1908). From 1900 to 1940 papers appeared at the rate of one or 

 two a year. At this point the first world-wide collection of monthly mean-sea- 

 level data appeared in print (I.A.P.O., 1940). As a result both new emphasis 

 and new scope were given to the problem. 



This chapter will summarize principally the results of the work during the 

 years since 1940. with full recognition of the fact that earlier workers had 

 already suggested all of the interrelationships between sea-level and other 

 physical phenomena that we will mention. A few of the earlier papers are 

 included in the references and these publications will lead the interested reader 

 to other sources. 



2. The Observed Seasonal Variations 



The International Association of Physical Oceanography (I. A. P.O.) of the 

 International Union of Geodesy and Geophysics had recognized the need for 

 more uniformity and availability of sea-level data, and, in 1933, it appointed a 

 Committee on Mean Sea-Level and its Variations. This committee undertook 

 to compile and publish monthly and annual values of mean sea-level at gauges 

 throughout the world. The first publication appeared in 1940 (I. A. P.O., 1940) 

 and additional compilations have been published at intervals since then 

 (I.A.P.O.. 1950. 1953, 1958, 1959). The presentation of the data in such useful 

 form made it possible to examine, for the first time, ocean-wide variations in 

 sea-level. Two papers appeared almost simultaneously summarizing the 



[MS received July, I960] 485 



