Salinity of the Ocean, its Variation in Oceanic Space and in Time 



161 



The change in time of a salinity disturbance at the surface of the sea caused by precipi- 

 tation has the form shown in Fig. 67. Case 2 on Fig. 66 corresponds completely to the 

 theoretical solution as far as the observations allow a comparison. For the time / 

 required to reduce a salinity disturbance produced in a time T to a fraction q by 

 turbulence alone the above equation gives 



for g = J 

 / = 0-56 T 



4 10' 



3-52 T 24-95 T. 



Thus a salinity disturbance produced by precipitation lasting one hour would fall 

 to one-tenth of its maximum value in about a day. Therefore, heavy rain can have an 

 appreciable effect on surface salinity and in a discussion of frequent rainfall this 

 circumstance deserves considerable attention. 



Fig. 67. Change in time in salinity due to precipitation at the surface according to the theory. 



In addition to the precipitation, the melting of icebergs which have drifted into 

 warm water can appreciably reduce the salinity in the remote and in the close surround- 

 ing waters. This process operates much more slowly than the precipitation but no data 

 for investigation are as yet available. 



The physical process should not be so very different except that the limited extent 

 of an iceberg will confine it to a smaller space and it will thus have to be considered 

 in three dimensions. 



2. The Horizontal Distribution of Surface Salinity 



The most detailed charts for the Atlantic Ocean are those prepared by Bohnecke 

 (1936) based on all the available data. More recent charts for all the oceans have been 

 given by Schott (1928, and in improved form 1934); corresponding charts are also 

 given in his geography of the Indian and Pacific Oceans (1935). Plate 5 shows such a 

 chart on an equal area projection. The salinity of the open ocean varies between less 

 than 33%o in the north-eastern Pacific and a little more than 37%o in the horse latitudes 

 of the North Atlantic. The range of variations is little more than 5%o. All three oceans 

 have zones of maximum salinity in the subtropics with maxima of more than 37-25%o 

 in the North Atlantic and the South Atlantic. In the open northern Indian Ocean 

 the Arabian Gulf has maximum salinity values of more than 36-5%o in sharp contrast 

 with the low sahnity of the Bay of Bengal. In the southern Indian Ocean towards 

 Australia there is a subtropical oval region with a maximum salinity of more than 

 36-0%o. 



