348 DR MURRAY ON THE DEEP AND SHALLOW -WATER MARINE FAUNA 



atmospheric pressure at all seasons in the southern hemisphere between the latitudes of 

 40° and 60° S. Over certain parts of these latitudes — for example to the south-east 

 of the Falkland Islands and to the south-east of New Zealand — the observations hitherto 

 made point to a mean pressure of 29*000 inches (736*6 mm.) and under. To the north 

 of this broad belt of low atmospheric pressure there is, about lat. 30° S., an area of very- 

 high atmospheric pressure, and we have many reasons for believing that an area of high 

 pressure rests on the Antarctic Continent in the far south. 1 



The inevitable result of this arrangement of isobars is that strong westerly winds with 

 large rain-fall and snow-fall prevail over nearly the whole area of the Southern Ocean. 

 These " Anti-Trades " blow with great persistency nearly due west, and having an 

 uninterrupted sea space over Avhich to blow they frequently rise to the force of a violent 

 gale, and. blow as such for several days in succession. Thus out of sixty-eight days 

 during which Sir James C. Ross lay at Kerguelen, a gale from the north-west is reported 

 on forty-five days. Among sailors the latitudes of these winds are known as the 

 "roaring forties." 



Waves and Currents. — The depth of the Southern Ocean and the great extent of 

 open sea over which they blow, enable the strong westerly winds to produce the longest 

 and highest waves anywhere encountered. Thus the "Novara" in 1857 records waves 

 36'1 feet (11 m.) in height about lat. 40° S., long. 31° E. Lieut. Paris in 1867 

 measured six successive waves 37*7 feet (11*5 m.) in height between the Cape of Good 

 Hope and the island of St. Paul's, and the Challenger in 1874 met the highest waves 

 of the voyage, viz., 23 feet (7 m.), between the Crozet Islands and Kerguelen. 



A much more profound and far-reaching influence of the westerly winds of the 

 Southern Ocean is the creation of enormous westerly drift currents. These currents are 

 fed by warm and saline water from the tropics, and by cold and less saline water from 

 the south polar area ; water must likewise sometimes be drawn towards the surface from 

 the deep layers, and a thorough mixing of the waters appears to take place in these 

 latitudes. So persistent is the action of the westerly winds in the Southern Ocean 

 throughout the year, that their influence appears to be felt right down to the bottom, 

 the density produced by varying degrees of salinity and temperature greatly facilitating 

 this downward movement. 



Temperature of the deeper layers of water. — The object of the Challenger's excursion 

 into the Antarctic Regions in 1874 was not to reach a high latitude, but chiefly to make 

 observations on the depth, temperature, and salinity of the ocean in the vicinity of the 

 Antarctic ice. The observations were of the greatest value, although not satisfactory 

 in all respects; they give some hints as to the kind of circulation that takes place, and 

 very clearly demonstrate the urgent necessity for further observations in these regions. 

 In this region of the Antarctic and Southern Oceans there appears to be a cold layer of 

 water sandwiched between a warmer one on the surface and a warmer and thicker one 



1 See Mlrhay, "The Renewal of Antarctic Exploration," Ueoyr. Journ., vol. iii. p. 17, 1894, with map of isobar* 

 and winds. 



