multiple layers of positive temperature gradients were ob- 

 served (fig. 33C). The subsurface maximum occurs most 

 usually at a depth of between 30 and 50 feet, in all cases 

 less than 50 feet. In most cases the salinity gradient is large 

 enough to counteract the temperature gradient, and the vertical 

 stability is maintained (fig. 34A). At some stations, however, 

 the increase in salinity in the layer of positive temperature 

 gradients was not sufficient to compensate for the decreasing 

 density caused by the temperature, and thus resulted in ap- 

 parent instability. In some cases apparent instability was 

 observed to result from vertical salinity gradients alone. 

 At station N13 (fig. 34B), for example, the surface layers 

 are isothermal, but the salinity decreases slightly with the 

 depth in the upper 20 meters. Such a combination of vertical 

 temperature and salinity structure leads to apparent insta- 

 bility in the upper layers. The fact that instability is present 

 is further substantiated by the bathythermogram at station 

 N21 (fig. 35A). One of the traces shown is the trace made 

 by the instrument while it was sinking through the water; the 

 other trace was made by the instrument while it was being 

 hauled in. If only one such bathythermogram had been ob- 

 tained, it could be supposed that there was something wrong 

 with the instrument; however, two bathythermographs were 

 lashed together at most of these stations, and nearly identical 

 traces were obtained from both instruments. The rapid change 

 in the thermal structure indicated here (the difference in time 

 between the two traces is but 1 or 2 minutes) may well be ex- 

 plained as the result of vertical convection set up by recently 

 established instability. Typical examples of vertical tem- 

 perature and salinity plots (fig. 35) indicate that the vertical 

 gradients increase with increasing latitude. The layers near 

 the bottom, especially at the northern stations, show low 

 temperatures of approximately 29 degrees F , and high sa- 

 linities of about 33 o/oo (fig. 35, B and C). A possible ex- 

 planation of the formation of this bottom water is given in the 

 discussion of the temperature-salinity relationships below. 



The temperature-salinity relationships for stations N10 

 through N15 are shown in figure 36. The T-S diagrams for 

 N10, Nil, N12, and N13 show characteristics similar to those 

 found at the central Bering Sea stations, though the temper- 

 atures at the Chukchi Sea stations are somewhat colder. It 

 would seem apparent from this similarity in T-S relationship 

 that the water at these Chukchi Sea stations results from a 

 northerly flow at all depths from the Bering Sea. 



The marked change in the T-S relationship at stations 



56 



