SPECIFIC GRAVITIES AND OCEANIC CIRCULATION. 337 



from Bahia to the La Plata. Observations made in this region would fill up the blank 

 to westward and southward of the " Challenger " and " Gazelle " courses. From the one 

 or two such observations made, it is evident that abnormally cold water fills the deep-sea 

 basin there, and, from its necessarily greater specific gravity, must exercise a powerful 

 influence on oceanic circulation. 



Owing to the low temperature of the higher latitudes the specific gravity there is 

 greatly in excess, but the excess diminishes with depth (Maps 2 to 7) as the temperature 

 of the ocean approaches to uniformity. The most remarkable differences are shown at 

 100 fathoms in the specific gravity in the intertropical part of the West Pacific as 

 compared with the specific gravities to the north and south. Thus, in the Yellow Sea 

 to the west of Nagasaki, the specific gravity is 1*0257 ; whereas, in the Sea of Japan, in 

 lat. 40°, it is 1*0272. A little to the north-east of Australia it is 1*0247, but to the 

 east of Sydney it is as high as 1*0271. 



At depths exceeding 1500 fathoms the geographical distribution of salinity and 

 specific gravity, as shown by the departure above or below their respective averages, 

 approximately coincide, owing to the great uniformity of temperature at these great 

 depths. Map 7 shows the distribution of the specific gravity at depths exceeding 1500 

 fathoms, and Map 9 the salinity. Map 9 confirms the important result that it is just in 

 those regions where the surface salinity is high that the bottom salinity and specific 

 gravity is also high ; and it is just in the regions where the surface salinity is low that 

 the bottom salinity and specific gravity is also low, thus showing a close connection 

 between the salinities of the surface and the bottom of the ocean. 



Another very striking feature is that these areas of high salinity carry down with 

 them to the bottom a comparatively high temperature, with which they are characterised at 

 less depths and at the surface.* Owing to this higher temperature the differences in the 

 geographical distribution of the specific gravities are less than those of the salinities, and 

 hence the movement resulting from the different degrees of saltness at great depths is 

 less than would otherwise be the case. The most conspicuous instance of these regions 

 of high salinities and temperatures down to the bottom is afforded by the North Atlantic. 

 If the extent of the area embraced by the high salinities be examined at the different 

 depths, the extent would appear rather to increase with the descent. 



In the Pacific Ocean, to the east of long. 140° E., no single observation yet made 

 shows a salinity above the average, thus indicating an expansion of the area of low 

 salinity in the North Pacific. The few observations off the west coast of South America, 

 from the equator southwards, are all under the average. Similarly, the area of low salinity 

 in the Gulf of Guinea is more pronounced and of wider extent at great depths than it is 

 at less depths and at the surface. 



It would appear from the outstanding features of the regions of exceptionally high 

 and exceptionally low salinities that the ocean through its depths is more completely 

 influenced by its downward movements than it is through its wide extent by its horizontal 



* See Challenger Report, Temperature Maps. 



