90 THE OCEAN FLOOR 



30% of the total is characteristic of calcareous oozes. 

 Since among the contributors to the calcareous shells 

 the genus Globigerina plays a predominant part, oozes 

 rich in forams are very often called Globigerina ooze, al- 

 though the number of shells from other genera may 

 play a considerable part in the composition. The com- 

 position of the foram shells from thermophile or from 

 more hardy species may vary considerably from one 

 layer to another in a long core. An analysis of the com- 

 position affords indications of climatic variations. 

 Layers in which the species characteristic of a high 

 water temperature are rare or missing are generally 

 assumed to have been deposited when the temperature 

 of the surface water, even on the equator, was reduced, 

 as during glacial periods. A careful foram analysis, 

 therefore, affords signs of paleoclimatological varia- 

 tions. In general, a high water temperature favors the 

 extraction of lime, so that John Wiseman, analyzing 

 an "Albatross" core from the equatorial Atlantic, has 

 from the lime content drawn inferences concerning 

 minor climatic variations during the last 14,000 years. 

 However, another factor influences the secretion of 

 lime from the water, namely the varying content of 

 phytoplankton, which, in its turn, depends on the abun- 

 dance or scarcity of nutrient salts required for an intense 

 vegetation — that is, on nitrates, phosphates, etc. which 

 are carried upward by upwelling deep water in the so- 

 called "regions of divergence." The locahzation as well 

 as the intensity of such divergences can be assumed to 



