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



At the beginning of the winter convection the temperature in this layer falls while 

 the salinity remains constant. When the specific volume of the first layer becomes the 

 same as that of the second there will be complete mixing of the two layers by con- 

 vection; the resultant layer will have the mean specific volume of the second layer, 

 given in Table 62 as 352, while the salinity will be the mean of the original salinities, 

 that is 3409%o. This specific volume and salinity correspond on the [r^l-diagram to 



Table 63. Heat available from convection and the readiness for ice formation at 



St. 888 "Andrey Perwoswanny". 



a temperature of 2-85 °C. Since the mean temperature of the two layers before mixing 

 was 3-19°C the convection process has been accompanied by a temperature fall of 

 0-34 °C and the amount of heat q^^ given off from the surface will be 0-34 kg cal/cm^ 

 by the equation on p. 96. Taking the third layer into consideration, it is now possible 

 to calculate the amount of heat to be removed from the two initial layers before the 

 third layer enters into the convection process with the two layers already mixed and 

 so on. Table 63 shows the final result of the mixing in each successive layer by con- 

 vection. However, the process proceeds in this way only until the sixth layer has been 

 included. After the inclusion of this layer the specific volume of all the layers cannot 

 reach the expected value of 300 even if the entire column of water has already been 

 cooled to the freezing point of salt water (— 1-8°C). At this depth the convection due 

 to reduction of the temperature ceases. In reality, however, after the temperature has 

 reached the freezing point ice begins to form at the surface and this causes an increase 

 in the mean salinity of the water column. From the [TlSJ-diagram it follows that the 

 saHnity must increase by 0-125%o for the specific volume to reach 300. From this in- 

 crease in salinity it is possible to calculate, using the equation on p. 96, the amount of 

 ice that must be formed to raise the salinity by this amount. The formation of ice 

 releases heat to the atmosphere; this is given by ^^ = 7-2 (c'/lOO), if e era of ice are 

 formed. The quantity of heat given off during the course of the convection process 

 down to and including the sixth layer is thus given by q^ + q^ which is 17-4 kg cal/cm^. 



As long as the convection extends only to layer 5, i.e. to a depth of 30 m, there is 

 no readiness for formation of ice in the water found at station 888. However, when 

 the convection includes deeper layers it increases rapidly and when the convection 

 extends to the bottom it requires a layer of ice 63 cm thick. 



This method presented above (Defant, 1949) is of course a little rough and not 



