332 DR ALEXANDER BUCHAN ON 



winds start on their course, forms a striking contrast with the high salinity in its western 

 part, towards which these winds blow. Salinity is also very high off the north-west 

 coast of Africa, towards which the prevailing winds of that part of the North Atlantic are 

 directed. The low salinity in the region of the Doldrums is well marked. Salinity is 

 also under the average in the Indian Ocean, and in the South Pacific from New Guinea 

 and north of Australia as far eastward, at least, as long. 130° W. 



On the other hand, salinity is under the average in latitudes higher than 40° north 

 and south, and over all but the whole of the North Pacific, so far as observations have 

 been made. Of all oceans, the North Atlantic shows the highest salinity, and the North 

 Pacific the lowest at 100 fathoms, just as happens on the surface of these oceans, and 

 from like causes. To these regions of low salinity fall to be added a very large portion 

 of the eastern division of the South Pacific, and probably the Gulf of Guinea, but here, 

 at this depth, observations are wanting. The northern parts of the Pacific and the 

 Atlantic offer a strong contrast to each other. Thus, to the north of Japan, the 12 

 observations within or contiguous to the Sea of Okhotsk, give a mean of 1*0247, or 

 0'0013 under the average ; whereas, in the Atlantic to the north of the Wyville-Thomson 

 Ridge, the mean of the 14 observations is 1*0257, or 0*0003 under the average. The 

 relatively high salinity here is due to the powerful oceanic current flowing thitherward 

 from the low latitudes of the Atlantic. The regions showing the lowest salinity are the 

 Sea of Okhotsk, and round the southern part of South America. 



This mode of distribution is substantially reversed on Map 2, showing the specific 

 gravities at the temperature of observation. If the intertropical part of the Pacific, 

 where upwelling from lower depths has been shown to occur, be excepted, the whole of 

 this ocean, between lat. 35° N. to lat. 30° S., exhibits specific gravities under the average, 

 the largest deficiencies being in the western parts of the ocean, where the rainfall is very 

 excessive, and where the temperature of the surface is abnormally high.* Elsewhere, 

 with the probable exception of the Gulf of Guinea, specific gravity is above the 

 average. 



By far the largest excess anywhere yet noted in the open sea is in the Arctic Ocean, 

 as determined by Mohn's observations, the mean of the 13 observations made at the 

 greatest depths being 1*0278, or 0*0017 above the general mean of the ocean. The mean 

 of the observations in, or near, the Sea of Okhotsk is only 1*0267, which is a very large 

 difference, when account is taken of the comparatively small range of the observations of 

 specific gravity. The observation of greatest specific gravity made by the "Challenger" 

 was 1*0278 in lat. 62° 26' S., and long. 95° 44' E., thus being the same as the mean of 

 the 13 observations in the Arctic Ocean. It is highly probable that an equally high 

 specific gravity characterises the whole of the Antarctic Ocean, and the adjoining portion 

 of the Southern Ocean south of lat. 55°. This high specific gravity of Antarctic 

 and Arctic waters plays an important part in oceanic circulation. The high specific 

 erravitv in these oceans, together with the head of water driven forward and accumulated 



* Challenger Report, Map 3< 



