The Three-dimensional Temperature Distribution and its Variation in Time 149 



not visible at all. It is caused by the intrusion of subantarctic intermediate water and 

 represents the same phenomenon as the isothermal layer or actual inversion in the 

 vertical distribution which was mentioned previously (see p. 123). South of 55° S. 

 the oceanic space all around the Antarctic is filled down to the greatest depths with 

 cold Antarctic water. The isotherms here steeply descend from the surface to 2500- 

 3000 m, clearly showing the extension of this cold-water type northward along the 

 deep basins that open to the south. 



This, like all other longitudinal sections, shows the considerable asymmetry in the 

 temperature distribution of the oceans. As previously mentioned this asymmetry 

 is caused by topographic conditions of the Atlantic, which allow only a spreading of 

 the cold heavy Antarctic bottom water towards the north. This is, of course, also the 

 case in the Indian Ocean but not entirely so in the Pacific where, although only to a 

 small extent, there is an Arctic component from the Okhotsk Sea to be taken into 

 account. The meridional temperature contrast between high-southern and high- 

 northern latitudes, which is especially well shown in the Atlantic and can also be seen 

 in the Pacific Ocean, is the main cause of the deep-sea circulation of these oceans and 

 also gives rise to their asymmetry relative to the equator. 



(c) Bottom Temperatures in the Three Oceans 



The question of the origin and the spreading of the lowermost layer of bottom 

 water in the oceans was raised at a very early stage in the development of oceano- 

 graphy — much earlier than the problems dealing with the oceanic circulation of the 

 middle layers. This was due to the existence of a greater amount of data for the 

 bottom layer than for the middle and deep layers, since bottom temperatures were 

 measured from cable-laying ships as well as from research vessels. The low tempera- 

 tures found in the bottom layers clearly indicated at an early stage a polar origin of 

 the bottom water and formed the main basis for the assumption of a deep-sea circula- 

 tion. An historical account of the exploration of the nature of the bottom water has 

 been made by WiJST (1936), who has also given a description and comparison of the 

 movements of the bottom water spreading out into the three oceans based on a critical 

 inspection of all the available data (Wust, 1938). Plate 4 gives a chart of bottom 

 temperatures on the deep-sea basins. The course of the isotherms is much more cer- 

 tain in the Atlantic than in the other incompletely explored oceans. The temperatures 

 given are potential temperatures in order to give a clear picture of the spreading of 

 bottom water influenced by the relatively large irregularities of the bottom topography. 

 Table 67 gives mean values for 10° latitude zones in the three oceans and for the total 

 ocean. In general, there is a continuous rise in the bottom temperature to be seen from 

 high southern latitudes across the equator as far as to temperate northern latitudes. 



The maximum temperature that can be taken as the boundary between Arctic and 

 Antarctic influences at the bottom is situated rather asymmetrically at 40° N. in 

 the Atlantic and at 30° N. in the Pacific. In almost all latitudes the coldest bottom 

 water is found in the Indian Ocean. The coldest water is in the deepest depressions 

 in the Atlantic South Polar Basin; the cold pole with — 0-92°C lies at the western 

 edge of the Weddell Sea, where according to Brennecke (1921) and Deacon (1937) 

 that thermo-haline stratification in the autumn and early winter exists, which per- 

 mits the ice-cold shelf water to sink by convection along the continental slope down 



