Currents 



109 



Figure 96. Temperature-depth 

 curves for open sea and for 

 waters below basin sills. Short 

 horizontal lines indicate depths 

 of sills and bottoms of basins. 

 From Emery (1954c, Fig. 2). 



TEMPERATURE 



4 5 6 



would characterize basins having sills 

 shallower than 500 meters. Silica, on the 

 other hand, is least in the basin having the 

 shallowest sill and greatest in the one hav- 

 ing the deepest sill, doubtlessly because in 

 the open sea the depth at which silica be- 

 comes uniform with depth is about 1000 

 meters, slightly deeper than for phosphate 

 and nitrate. 



In summary, temperature, salinity, oxy- 

 gen, and sihca differ from basin to basin, 

 but within individual basins each is nearly 

 uniform from sill depth to bottom and nearly 

 equal to values in the open sea at the depth 



of the basin sill. The range of variation 

 from basin to basin as compared with error 

 of measurement is greatest for temperature; 

 moreover, temperature is least subject to 

 change by biological activities. Thus, tem- 

 perature is the best of these parameters for 

 characterizing the basin water and indicat- 

 ing its source. Water at the bottom of San 

 Nicolas Basin must have come either from 

 the northwest or the southeast, owing to 

 blocking of flow from other directions by 

 the high basin side slopes, some of which 

 are capped by islands. It is obvious, how- 

 ever, that the water could not have come 



