258 WOOSTER AND BEID [CHAP. 11 



Furthermore, the existence of coastal countercurrents, either at the surface or 

 below, is well established (Reid, I960, 1962; Wooster and Gilmartin, 1961). 



The speed of the eastern boundary currents can be estimated from drift 

 charts or from dynamic charts ; in the California and Peru Currents, GEK 

 measurements are available. These estimates indicate that the average speed 

 is half a knot or less, in contrast to the extreme speeds of four knots or more in 

 the western boundary currents (Stommel, 1958). 



The depth to which eastern boundary currents extend has not been deter- 

 mined by direct measurements. Indications are available, however, from the 



GEK MEASUREMENTS J35 

 10 cm/sec 



EORO \,5cm/«c \ 



Fig. 4. Measurements of surface velocity by geomagnetic electro-kinetograph, January- 

 March, 1954, superposed on contours of dynamic height anomalies (0 to 500 db) for 

 same period. GEK measurements averaged over 24 h west of 123°W, over 12 h east 

 of 123°W. (Prepared by Reid from data of Scripps Institution of Oceanography, 

 California Department of Fish and Game, and Pacific Oceanic Fishery Investigations 

 of the Bureau of Commercial Fisheries.) 



sub -surface distribution of density or temperature, which closely parallels 

 density (Figs. 6a- 10a). In general the offshore slope of the isopycnals decreases 

 significantly below about 500 m. Furthermore, transport calculations relative 

 to the 1000-db or 2000-db surfaces are little different, suggesting either that there 

 is no motion at these depths, or that motion is the same at both levels. The 

 presence of coastal undercurrents, especially in the Pacific (see page 273), is 

 additional evidence that surface flow is restricted to a relatively shallow layer. 

 It seems clear that the principal equatorward flow is above 1000 m, and in 

 most places is above 500 m. In contrast, in the Gulf Stream, sub-surface iso- 

 therms still slope strongly at depths of several thousand meters (Fig. 5), and 



