THE PACIFIC OCEAN 



101 



For this purpose we have plotted in figures 13 to 18 

 all observations below the 100-meter level, using verti- 

 cal lines to designate the observations between 100 and 

 500 meters, 500 and 1500 meters, and below 1500 me- 

 ters. The observations have been combined into groups 

 which show the characteristic tS relation within certain 

 regions. The limits of these regions have been deter- 

 mined by means of the tS cur-'es and may thus be re- 

 garded as natural subdivisions. Within each region we 

 find, on the whole, the same tf relation at the different 

 stations, and in most cases the transition from one type 

 of tS relation to another is quite distinct. Cases exist in 

 which the transition from one region to another, however, 

 takes place within an area which is so great that obser- 

 vations at Some stations show a tS relation which lies 

 between the characteristic relations of the two neighbor- 

 ing regions. 



The areas within which the tS relation is nearly the 

 same have been indicated in figure 19 in which they have 

 been numbered from 1 to 14. Figure 20 shows the tS 

 curves for each of these regions. The numbers of the 

 regions are entered on the corresponding curves. The 

 curves represent the mean curves as derived from the 

 diagrams in figures 13 to 18 in which the single obser- 

 vations have been entered. From these single diagrams 

 it is seen that within every region the water is typically 

 stratified. Water of a low temperature is found at great 

 depths only, water of a temperature about 3° to 7" be- 

 tween the levels 500 and 1500 meters, and water of a 

 high temperature is found above 500 meters. It is possi- 

 ble, therefore, even on the average curve, to indicate the 

 depth interval at which water of certain characteristic 

 temperature and salinity is found. This hasbeen accom- 

 plished in the average curves on figure 20 by drawing the 

 tS curve which shows the characteristic relation below a 

 depth of 1500 meters as a very heavy line, the curve be- 

 tween 500 and 1500 meters as a moderately thick line, 

 and the curve above 500 meters as a thin line. The 

 moderately thick line represents water which is found 

 between 500 and 1500 meters only, but on the thin line a 

 mark has been placed, indicating the ma.ximum stretch 

 along the tS curve which represents water below the 500- 

 meter level. The part of the thin curve to the right of the 

 mark thus represents water which never is found below 

 500 meters, whereas the part of the thin curve to the 'eft 

 of the mark represents water which may be found both 

 above and below the 500-meter level. 



It is not necessary to enter on the characteristic 

 properties of the water below 1500 meters within the 

 deep areas, because the water is evidently of nearly the 

 same character within all areas. From the course of 

 the tS curve it is evident that the deep water of the low- 

 est temperature has the highest salinity, and also that 

 the salinity of water of a temperature of 2° decreases 

 from the south toward the north. Distinct differences be- 

 between the different areas are found above the 1500- 

 meter level and we shall discuss these more fully. 



Region 1 comprises the mqst southern area of the 

 Pacific which was investigated, and lies to the west of 

 the South American coast. In this area we find a salinity 

 minimum within the interval 500 to 1500 meters which 

 is characterized by the corresponding values, S = 34.25 

 per mille, t = 5.°2. Above 500 meters we find that water 

 of a high temperature has a lower salinity than is found 

 at any depth below 500 meters. 



Region 2 lies to the north and northwest of Region 1 

 and differs mainly as to the character of the water above 



500 meters. The water between 500 and 1500 meters is 

 practically of the same character as in the more southern 

 region, but both salinity and temperature appear to have 

 increased. The corresponding values at the salinity 

 minimum are S = 34.29 per mille and t = 5.°5. 



Regions 3, 4, and 5 lie between south latitudes 10° 

 and 20°: Region 3 off the coast of South America, Re- 

 gion 4 between longitudes 95° and 130° west, and Region 



5 between longitudes 130° and 175° west. Region 5 ex- 

 tends slightly more toward the north than does Region 4. 

 In these three regions we find practically the same tS 

 relation in the interval, 500 to 1500 meters. The cor- 

 responding values at the salinity minimum are: in Re- 

 gion 3 S = 34.51 per mille, t = 5.°6: in Region 4 S =34.52 

 per mille, t = 5.°6; and in Region 5 S = 34.40 per mille, 



t = 6.°0. Above the 500-meter level considerable differ- 

 ences exist between these three regions, but we have al- 

 ready dealt sufficiently with these differences when de- 

 scribing the horizontal and vertical distribution of tem- 

 perature and salinity. 



Regions 6 and 7 comprise equatorial areas; one. 

 Region 6, off the South American coast, and the other, 

 Region 7, in the central part of the Pacific. Below a 

 depth of 100 meters we find practically the same tS re- 

 lation at stations 150 to 158 and stations 98 to 100 and 

 these have, therefore, been combined. It should be noted 

 that the northern limit of Region 7, however, does not 

 run east and west but approaches the equator more in 

 the western than in the eastern part of the ocean. The 

 tS relation below the 500-meter level is similar within 

 regions 6 and 7, the only difference being that in Region 



6 higher temperatures are found at 1500 meters. The 

 lowest salinity values between 500 and 1500 meters are 

 about 34.55 per mille and the corresponding tempera- 

 ture is 5.°6. 



Regions 8 and 9 stretch together across the Pacific 

 in a direction from east-northeast to west-southwest. 

 Within these regions we find some differences between 

 the tS relation in the eastern and western parts of the 

 ocean, but the general features of the relation are simi- 

 lar. In the eastern part the salinity decreases more 

 rapidly with decreasing temperature and reaches a min- 

 imum values of 33.98 per mille where the temperature 

 is 8°, but in the wostern part the decrease of the salin- 

 ity is slower and a minimum value of 34.23 per mille is 

 reached where the temperature is 9.°5. 



Regions 10 and 11 to the north of regions 8 and 9 

 show a similar difference between the relations in the 

 eastern and western parts of the ocean. In the eastern 

 part the salinity decreases rapidly to a minimum of 



33.97 per mille where the temperature is 6°, whereas 

 in the western part a more gradual decrease takes 

 place, reaching to a minimum of 34.10 per mille at a 

 temperature of 6f5. 



Region 12 lies off the coast of North America and 

 northeast of Region 11. In this region the salinity de- 

 creases constantly with decreasing temperature, but 

 the decrease is slow where the salinity has a value of 



33.98 per mille and the temperature is 6°, correspond- 

 ing to the characteristic temperature and salinity at the 

 minimum on the tS curve in Region 11. 



In Region 13, which lies off the coast of Japan in lat- 

 itude 40°, and in which only the three stations--115, 11 C, 

 and 117--were occupied, we find a tS relation which is 

 rather similar to the relation in regions 10 and 11, but 

 with greater variations. The salinity decreases rapidly 

 with decreasing temperature to a minimum of 33.78 per 



