94 



OBSERVATIONS AND RESULTS IN PHYSICAL OCEANOGRAPHY 



about 25° at station 39. At station 40 the convection 

 layer has a thickness of less than 23 meters, the salin- 

 ity is slightly above 34 per mille but the temperature is 

 only 20.°4. At the next stations, 69 to 72, we also find a 

 very thick convection layer which never reaches to a 

 depth of 40 meters. The surface salinity is higher here, 

 being above 35 per mille, but the temperature is low 

 especially at station 71 which has been taken at a short 

 distance from the coast. Proceeding toward the south 

 along the section we find that the convection layer re- 

 mains thin at all stations, but the transition from the 

 convection layer to the deeper layers becomes more and 

 more gradual. This is especially evident when we take 

 the density into account. At station 71 we have, for in- 

 stance, an increase in a^ from 24.05 at 19 meters to 

 25.36 at 40 meters, whereas at station 60, <r^ increases 

 only from 25.32 to 25.51 between 24 and 47 meters. 



The heating by radiation and contact with the atmos- 

 phere and the influence of evaporation and precipitation 

 are primarily responsible for the temperature and the 

 salinity of the convection layer, but transport of water 

 from deeper layers may also be of importance. In this 

 place we shall especially emphasize that the low salinity 

 in the region of Central America must be ascribed to 

 the influence of precipitation because we have no inflow 

 of water of low salinity to this region, and because no 

 large rivers carry considerable quantities of freshwater 

 into the sea. The high salinities off the Peruvian coast, 

 on the other hand, must be attributed to the effect of 

 evaporation because this water is transported toward the 

 coast from the south where the salinity is lower, or to 

 the effect of "upwelling" which brings water of higher 

 salinity to the surface. 



Below the convection layer we find a more or less 

 rapid decrease of the temperature with increase with 

 depth. The decrease is especially very rapid at the 

 stations which have been taken at a short distance from 

 the coast of Peru, but is more gradual at the southern 

 stations. The isotherm of 15° sinks from stations 60 to 

 67 and rises between stations 67 and 70. The isotherm 

 of 10° also sinks between stations 60 and 67 but up to 

 station 71 this isotherm continues sinking and runs hori- 

 zontally north of this station. The isotherm of 5°, on the 



other hand, runs almost horizontally up to station 67 and 

 sinks from this station as it proceeds to the north. The 

 rise of the isotherm of 15° between stations 67 and 70 

 indicates an accumulation of cold water in the upper 

 layer; but this accumulation does not reach below the 

 level of the 10° isotherm and is thus a phenomenon of the 

 troposphere. 



The distribution of the salinity is much more com- 

 plicated except in the northern part of the section where 

 the salinity decreases regularly down to a depth of 1000 

 meters. South of station 72 we find many irregularities 

 in the vertical variation of the salinity at the different 

 stations, but in the section two major features are seen. 

 The salinity of the water above a depth of about 200 me- 

 ters increases, on the whole, from south to north. As 

 already mentioned, this increase must be attributed to 

 the influence of evaporation because it is more rapid at 

 the surface. The tongue of low salinity, which extends 

 from station 68 to station 70 at a depth of 150 to 200 me- 

 ters, is probably associated with an upwelling movement 

 in the upper layers. Below a level of 400 meters we find 

 a layer of minimum salinity representing the intermedi- 

 ate antarctic current. The axis of the lowest values 

 sinks from a little less than 500 meters at station 60 to 

 about 700 meters at station 69, and in the same distance 

 the salinity increases from 34.2 to 34.5 per mille. The 

 axis practically follows the isotherm of 6°. To the north 

 of station 69 water of salinity between 34.5 and 34.6 per 

 mille is found between depths of about 500 and 1500 me- 

 ters. 



The deep water below a level of 2000 meters has a 

 very uniform character. The salinity increases slightly 

 toward the bottom. 



In the Peruvian Basin the temperature appears to 

 have a constant value of l.°83 below a level of 2700 me- 

 ters, but at the southern stations, 60 to 66, the tempera- 

 ture decreases with increasing depth. The lowest tem- 

 perature was found at station 60 where l.°23 was observed 

 at a depth of 3617 meters, 400 meters above the bottom. 



Section IV. --Section IV, comprising stations 45 to 51, 

 also represents a section approximately north and south 

 in the same general region but at a greater distance from 

 the coast. Here the convection layer has a considerably 



Table 8. Deep-sea temperatures (t) and salinities (S) in the Pacific arranged according to latitude 



53 N 153 E 

 40 N 120 W 



12 1.91 (12) 34.58 (12) 



40 N 140 E 



20 N 120 W 29 2.04(29) 34.59(29) 



18 2.19 (16) 34.62 (16) 



44 2.20 (42) 34.62 (42) 



20 2.17 (19) 34.62 (19) 



Maximum - minimum 0.29 0.04 



1.71 (11) 34.61 (11) 



1.74 (27) 34.62 (27) 



1.84 (15) 34.63 (15) 



1.89 (41) 34.64 (41) 



1.90 (18) 34.65 (18) 

 0.19 0.04 



1.62 (7) 34.63 (7) 



1.60 (19) 34.63 (19) 



1.69 (12) 34.64 (12) 



1.77 (24) 34.66 (24) 



1.76(12) 34.67(12) 



0.17 0.04 



Numbers in parentheses indicate number of stations included. Salinities probably 0.03 o/oo too low. 



