224 



BULLABD 



[chap. U 



are only roiiglily known but a uniform reduction in conductivity by 4% should 

 avoid serious systematic error. The relation (3) then becomes 



R = 168 + 678z^;. 



(4) 



The conductivity that is required in the calculation of heat flow is the reci- 

 procal of the mean resistivity. Since the resistivity is linearly related to the 

 water content it may be found from the mean water content. The water 

 content at a point in a core may vary from about 25 to 60%, but the mean 

 down a core is much more uniform. For example, 10 cores of Globigerina ooze 

 from the north-eastern basin of the Atlantic all had water contents between 48 

 and 40% and mean conductivities between 0.0020 and 0.0023 cal/cm sec °C 

 (Bullard, 1960). 



700 1- 



600 



U 



u 



0) 



E 

 u 



V 



u 



c 





500 



400 



300 



200 



100 



20 40 60 



Water content (per cent wet weight) 



80 



100 



Fig. 5. Relation between thermal resistivity and water content. O red clay, # Globi- 

 gerina ooze, X mud. 



To calculate the thermometric conductivity, kfap, the densit}^ p, and the 

 specific heat, a, of the sediment are required. If the sediment can be regarded 

 as a mechanical mixture of particles of mean density ps, the spaces between 

 \\'hich are filled with water of density p^, its density is given by 



1-1 — 



ps~^+{pw~^-ps''^)w. 



Naturally, the best value for ps varies with the type of sediment. A least squares 

 reduction of the 44 densities given in Bullard (1956) and Bullard and Day (1961) 

 gave 2.56 g/cm^ for Globigerina ooze, 2.64 for red clay and 2.34 for mud; all 

 the data combined gave 2.51 with a standard deviation of 3%. If this accuracy 



