But we have seen that at the examined station during cooling under calm conditions, the crit- 

 ical depth of vertical circulation was only 18 m, so that the amount of heat released to the atmos- 

 phere was only 18.5 kg-cal/cm^. 



Thus we find that before the start of cooling, the surface layers of a given station are mixed 

 to a depth of 25 m, before the start of the ice formation, 3. 8 kg-cal/cm more should be released 

 to the atmosphere during calm conditions. It should be noted that such an increase in the index of 

 freezing takes place only if wind mixing encompasses layers deeper than the critical depth of verti- 

 cal circulation; in our example, below 18 m. But, if under the same conditions wind mixing pro- 

 ceeds to the level of temperature inversion (if in the given region such exists) there may be such an 

 increase in the index of freezing that ice formation in a given region becomes completely impos- 

 sible. This circumstance should be considered when computing the indices of freezing. 



From all this , it is clear that if in the pre-winter period we set up a network of oceanographic 

 stations in the region of interest to us, plot on a chart the indices of freezing computed for each of 

 them separately by the method described earlier, and draw the corresponding isolines, we may in 

 first approximation, judge at which of the stations, all other conditions being equal, the tempera- 

 ture of the sea surface will drop first to the freezing point, and at which it will drop last, or, in 

 other words, where ice formation will set in earlier and later. 



Naturally, in addition to the indices of freezing, we need to know the rate of cooling of the 

 separate regions of the sea, i.e. , the amount of heat released from the surface of the sea to the 

 atmosphere during 24 hours under various conditions, taking these conditions into account we could 

 judge approximately the time when freezing would begin. 



LITERATURE: 65. 



Section 32. Features of Vertical Winter Circulation 

 in the Shallows 



Let us assume that from observations , the horizontal oceanographic gradients at the initial 

 moment in the examined sector of the sea are equal to 0, while the vertical gradients are uniform, 

 i.e. , that the sea consists of horizontal layers, which are uniform with respect to temperature and 

 salinity. Let us further assume that at a certain moment the vertical circulation extends to the top 

 of a submarine bank (figure 20). At this moment, "ventilation" of the top of the bank begins, as 

 follows, the surface layers (oxygen enriched due to exchange with the atmosphere and enriched with 

 nutritive matter as a result of the photosynthetic action of plants) will be continuously mixed with 

 the bottom layers. 



Figure 20. Diagram of the creep 



of cool waters along the 

 slopes of the shore. 



79 



