486 TATTULI.O [chap. 22 



large-scale features that could be detected (Lisitzin, 1955; Pattullo. Munk. 

 Revelle and Strong, 1955). 



Lisitzin and the American group agreed in their conclusions that long sections 

 of the coastlines undergo similar seasonal fluctuations in sea-level, i.e. the 

 variations are "coherent" over rather long distances. Furthermore, at the same 

 latitudes on opposite sides of the oceans (and, as far as could be determined, 

 on islands in midocean) the seasonal variations are similar. Lisitzin found 

 evidence of four principal zones in both the Atlantic and Pacific Oceans ; the 

 Americans agreed as to three areas but did not identify the fourth. Within 

 each zone all gauges showed similar variations, but there was a marked dif- 

 ference from zone to zone. From high northern latitudes to about 45°N, the 

 maximum elevations were observed in winter (December) ; from 45°N to the 

 equator maxima occurred earlier, usually in September ; from the equator to 

 about 45°S maxima occurred in March, and (Lisitzin only) south of 45°S the 

 maximum was usually in June. 



These results were convincing evidence that at least some of the factors 

 causing the changes must be of large areal extent. Lisitzin offered the suggestion 

 that changes in oceanic circulation could effect the observed results. Pattullo 

 et al. proposed no explanation, but pointed out that (1) astronomical tides are 

 apparently not large enough to be the principal cause, (2) atmospheric pressure 

 effects at the gauges do not seem to be large enough either, (3) between 40°N 

 and 40°S the observed changes bear considerable similarity to changes in level 

 that can be deduced if only the volume, not the mass, of sea- water changes 

 seasonally at any given point, and (4) outside the latitudinal band 40°N to 40°S 

 changes in water volume are not large enough to account for observed changes 

 (see also steric levels. Volume I. Chapter 16). 



In an attempt to clarify the situation further, several dozen additional tide 

 gauges were installed during the International Geophysical Year (I.G.Y.), 1957 

 and 1958, and operation of some of them was continued through the Inter- 

 national Geophysical Cooperation (I.G.C.), 1959. The sites were chosen, when- 

 ever possible, at oceanic islands, with the explicit purpose of providing data of 

 oceanic character to compare with the more numerous records already taken 

 along coastlines. At the same time, temperature and salinity measurements were 

 made, to a depth of a few hundred meters, in deep water offshore from each 

 gauge. It was hoped that these collections would make possible a better com- 

 parison between changes in water volume and recorded changes in elevation of 

 the sea surface. 



The results of the tide-gauge measurements are summarized in Figs. 1-4. To 

 keep the description as nearly synoptic as possible, I.G.Y. (and some I.G.C.) 

 data have been used where available. Where adequate I.G.Y. data either were 

 not collected or have not been published in time for inclusion in this volume, 

 data collected in earlier years have been added, in order to complete the 

 picture. These non-synoptic data are principally in the Southern Hemisphere ; 

 they include the Antarctic data, gauges along the west coast of South America 

 and the east coast of Africa, and all gauges in Indonesia and New Zealand. 



