The column is then said to be partially mixed down to the second level. 

 Complete mising is achieved by cooling the partially mixed column until 

 its density, <r lt 2 , equals that of the original second layer, <r 2 . 

 This mixing may be accomplished merely by changing the temperature of 

 the partially mixed column, provided the water is not cooled below its 

 freezing point. If the temperature change necessary for completely mix- 

 ing the column requires a temperature below the freezing point, ice will 

 form and the salinity of the remaining water in the column will be in- 

 creased. The mixing process is carried out layer by layer until the po- 

 tential heat loss is greater than the possible heat loss for a given ice 

 season. 



For convenience the expressions "partially mixed" and "completely 

 mixed" have been used in connection with the ice potential computations. 

 Two layers of water are termed "partially mixed" when the mixed column is 

 defined completely by the means of the temperatures and salinities of the 

 two original layers (i.e., no heat loss is involved). A "partially mixed" 

 layer becomes "completely mixed" when the density of the partially mixed 

 layer equals that of the original lower layer, with the density of the 

 original lower layer remaining fixed throughout the process. In this 

 latter case a heat loss is necessary, provided that the density distribu- 

 tion is stable. Temperature and salinity changes which result from this 

 mixing model can be easily read from a T-S nomograph, or can be computed 

 by use of standard hydrographic tables, (H.O. Pub. No. 615) 



Complete mixing can be accomplished only by releasing o gram calo- 

 ries of sensible heat from the water column one square cm in cross section. 

 Quantitatively, <W n } = c p hAT where c is the specific heat of sea 

 water P w is the density of sea water, h is the depth to which complete 

 mixing reaches (or volume of h aa?) r and AT W is the amount of heat lost 

 in changing the partially mixed column to a completely mixed column. When 

 it is necessary to change the salinity of the column in order to achieve 

 complete mixing, latent heat is involved in the process as well as sensible 

 heat. Since a known percentage of the salt is frozen out of the ice, it 

 is possible to write an expression for the latent heat as a function of 

 the salinity change. Consequently, the ice accretion corresponding to a 

 given salinity change can be expressed mathematically. As written by 

 Defant, the ice thickness is given by 



fi- 



has 



c /° w bS (i) 



where S is the salinity of the partially mixed column and b is the per- 

 centage of the salts frozen out of the ice. The latent heat can now be 

 evaluated from the well-known formula q^ (Z) « K£ (Z), where K is the 

 latent heat of fusion, which decreases with increasing salinity of the 

 ice. The total potential latent heat is given by 



i 



qdz = Q,(h) ( 2 ) 



