SECT. 1] 



THE FLOW OF HEAT THROUGH THE FLOOR OF THE OCEAN 



223 



good approximation for times large compared to r ^//c. For the needle used, r^JK 

 is about 0.8 sec and a straight line is obtained when 6 is plotted against In t for 

 all times between 10 sec and 10 min. 



The results show that the conductivity of a sediment depends on its water 

 content and varies very little with the nature of the mineral particles. It is, 

 therefore, possible to calculate the conductivity if the water content is known . 

 The observations can be represented satisfactorily by the theoretical expression 

 for the conductivity of an assembly of spheres distributed in water (Bullard, 

 Maxwell and Revelle, 1956; Horai and Uyeda, 1960). The comparison for 44 

 specimens measured by Butler and Ratcliflfe is shown in Fig. 4. Empirically it 



40r 



o 0-14.9% CaCOs 

 A 15-29.9% CaCOs 

 + 30-100% CaCOj 



30- 



.J- 20- 



c 

 o 

 o 



10 



'"^^o 



%. 



Theoretical curve for 



P /P, = 'z?, I<^/K =0-2 



Theoretical curve for 



40 60 



Water content (wet weight), w 



80 



100 



Fig. 4. The variation of the thermal conductivity of ocean-bottom sediment with water 

 content. The curves are theoretical expressions for spheres of density ps and con- 

 ductivity kg dispersed in water of density pi^ and conductivity knj. (After Bullard 

 et al., 1956, fig. 4.) 



is found that the thermal resistivity (the reciprocal of the conductivity) is 

 linearly related to water content as is shown in Fig. 5 (Bullard and Day, 1961). 



The best straight line is 



R = (161±14) + (651±30)^i;, 



(3) 



where B, is in cm sec °C/cal and w is the water content expressed as a proportion 

 of the wet weight. There is no systematic difference between the conductivities 

 of red clay and Glohigerina ooze of the same water content. 



The measurements were made at a room temperature of about 25°C and at 

 atmospheric pressure. The values required are those at the temperature and 

 pressure of the sea floor, which may be taken as 3°C and 500 kg/cm^, Butler has 

 shown that the decrease in temperature will reduce the conductivity by 6% 

 (Ratcliffe, 1960). If the pressure coefficient is the same as that for pure water 

 the increase in pressure will raise the conductivity by 2 to 3%. The corrections 



