364 PEECY SLADEN TRUST EXPEDITION. 



As regards the range of temperature in the surface waters of the Indian Ocean *, 

 there is a belt in which the range of temperature thi'oughout the year at any one place 

 is very small (less than 10° F.), ci'ossing the ocean from the east coast of Africa (north 

 of Madagascar and south of Cape Guardafui) to the shores of the Malay Peninsula and 

 Sumatra, lying mostly to the north of lat. 10° S., and filling up the greater part of the 

 Arabian Sea and the Bay of Bengal ; observations within this belt show that the range 

 of temperature within any 2° square is less than 10° P., and the extreme range in 

 different parts of the area is not more than fifteen degrees — from 72° to 87° F. This 

 is essentially the region of coral-reefs. 



To the north and south of this tropical belt of small range, the range of temperature 

 in the surface waters gradually increases, until at the heads of the Persian Gulf and Red 

 Sea in the north, and to the south of the Cape and Madagascar (in lat. 40° S.) in the 

 south, a range exceeding 30° F. is found; the observations show temperatures ranging 

 from 65° to 96° F. at the head of the Persian Gulf, from 60° to 93° F. at the head of 

 the Bed Sea, and from 36° to 75° F. in the region to the south of the Cape and 

 Madagascar. 



Proceeding south of the latitude of 40° S. the range of temperature again decreases, 

 imtil to tlie south of lat. 55° S. it does not exceed 10° F. at any one place throughout 

 the year, and in the region of perpetual ice in the far south the extreme annual range 

 of surface temperature does not exceed 5° F. in any single 2° square, and the extreme 

 range within the whole area is not more than 22° from the freezing-point of sea-water 

 (about 28° F.) to about 50° F. 



Beneath the surface the seasonal variation of the temperature of the water at any 

 one place rapidly decreases, so that at a depth of 50 fathoms the range of temperature 

 in any particular locality does not apparently exceed 2° F., and at a depth of 100 

 fathoms all seasonal variation is supposed to have disappeared, hence all temperature 

 observations recorded for depths of 100 fathoms and all greater depths are looked upon 

 as good annual means f. 



100 fathoms. — At a depth of 100 fathoms a large extent of the Indian Ocean has a 

 temperature above the mean for the whole ocean for that depth, viz. 60° '7 F. The highest 

 temperature (70° F.) is near the centre of the ocean about long. 80° E. and lat. 18° 8. 

 The same high temperature is found a little to the east of the Strait of Bab-el-Mandeb, 

 from which point eastwards it gradually falls to 60° F. The lowest temperature (56° F.) 

 overspreads a considerable area lying east and west to the south of Ceylon and north of 

 the Equator. This area lies in the region of the meeting of the north-east and soutli-east 

 trades. The low specific gravities in the Bay of Bengal seriously prevent the diffusion 

 downwards of the higher temperatures of the surface, and in this region there is no doubt 

 that upwelling takes place during the winter months when winds are northerly. 



* See Murray, "On the Annual Range of Temperature in the Surface "Waters of the Ocean, and its Relation to other 

 Oceanograpbical Phenomena," Geogi-. Journ., vol. xii. p. 113 (1898). 



t Certain recent observations, however, seem to indicate that even in very deep water there may be a slight 

 Viiriation due to seasonal or other causes (see Peake and Murray, " On the Results of a Deep-sea Sounding Expedition 

 in the North Atlantic during the Summer of 1899,''Roy. Geogr. Soc. Suppl. Papers, 1901, p. 10). 



