THE NORTH ATLANTIC OCEAN 



85 



At the surface the temperature (fig. 210; I-B) is uni- 

 form and high--between 25° and 30° C. In the Caribbean 

 Sea we find in the upper layers a greater accumulation 

 of warm water than in the Atlantic, the isotherms of 10° 

 and 15° being found at greater depths in the Caribbean. 

 The observations below a depth of 1000 meters in the 

 Caribbean Sea indicate that below this depth the temper- 

 ature remains almost constant. At all stations it de- 

 creases slightly with increasing depth, but the decrease 

 is so slow that the deepest observation gives a tempera- 

 ture of 4°07 at a depth of 2287 meters, against 3.°20 at 

 the same depth outside the Caribbean Sea (station 30). 

 The observations of the Dana in the Caribbean Sea 

 (Jacobsen, 1929) give, on an average, a similar result, 

 as is evident from table 3. 



Table 3. Temperature below 1000 meters in the 

 Caribbean Sea according to the Dana and the Carnegie 



The observations at great depths by the Dana indi- 

 cate a rise of the temperature from a level of 2000 or 

 2500 meters toward tbe bottom, corresponding approxi- 

 mately to adiabatic equilibrium. 



In the Atlantic part of Section II the temperature de- 

 creases regularly toward the bottom, the lowest value 

 observed being 2.°17 at a depth of 4703 meters at station 

 30. 



The salinity curves in Section II (fig. 101; I-B) show 

 a maximum below the surface at a depth of about 100 

 meters. This maximum, as already pointed out by Jacob- 

 sen, is probably related to the existence of currents 

 which carry salt water from the central part of the At- 

 lantic Ocean to the south. 



The salinity minimum at a level of about 700 meters, 

 indicating the intermediate Antarctic Current, is clearly 

 seen. It also is evident that this intermediate water pen- 

 etrates the Caribbean Sea, but here it probably becomes 

 mixed with the overlying and underlying water since the 

 salinity of the intermediate water increases somewhat 

 when proceeding to the west. These features have been 

 treated thoroughly by Jacobsen, who especially has ex- 

 amined the mixing of the water masses of different ori- 

 gin. 



The Carnegie observations indicate a decrease in 

 the salinity of the water of the Caribbean Sea below a 

 depth of 1000 meters, but this decrease is probably not 

 a real feature in spite of the fact that it is shown by the 

 observations at two stations, 33 and 34. At the former 

 a salinity of 34.76 per mille was observed at a depth of 

 2075 meters, and at the latter a salinity of 34.74 per 

 mille at 2287 meters. The observations of the Dana be- 

 low a level of 1200 meters, however, show a uniform 

 salinity varying between 34.95 per mille and 34.98 per 

 mille. The observed values at the greatest depths of 

 stations 33 and 34 therefore have been rejected and, in- 

 stead, it was assumed that the salinity at a level of 2000 

 meters was 34.96 per mille at lx)th stations. When car- 

 rying out the dynamic calculation this value was used. 



The Deep Water of the Atlantic 



Temperature. --Helland-Hansen (1930) has shown 

 that the Challenger observations indicate that the bottom 

 temperatures decrease with increasing depth in the 

 Western Atlantic Deep, but increase in the Eastern At- 

 lantic Deep. Introducing the potential temperature, 9, 

 defined as the temperature which a water particle attains 

 when it is raised adiabatically to the surface of the sea, 

 he found that the potential temperature decreases with 

 increasing depth in the Western Deep but remains con- 

 stant in the Eastern Deep. The a;)solutf values are low- 

 er in the Western Deep and this result is confirmed by 

 the observations of the Dana. 



We have table 4 as a result of an examination of the 

 potential temperature of the water below a depth of 4000 

 meters according to the Carnegi e observations. The 

 data are too few to permit any conclusions as to the av- 

 erage conditions in the two basins, except that the poten- 

 tial temperature is lower in the Western Deep than in the 

 the Eastern. It may be added that all values in the East- 

 ern Deep are lower than the average value, 2.° 15, found 

 by Helland-Hansen from the Challenger observations. 



Salinity . --Table 5 is the result of the observations 

 of salinity below a level of 4000 meters. The salinity 

 appears to be slightly lower in the Eastern Deep, but the 

 values are too few and show too much scattering to per- 

 mit any definite conclusions. The absolute values are, 

 as stated on page 72, probably 0.03 to 0.04 per mille too 

 low. 



Table 4. Values of potential temperature, Atlantic 

 deep water, Carnegie. 1928 



Western deep 



Station Depth 



Eastern deep 



Station Depth 



14 



15 



14 



15 



Mean 



4407 



34.88 



4411 



34.84 



