910 



EMILIANI AND FLINT 



[chap. 34 



Marked variations of the weight percentages of the foraminiferal component 

 and of the carbonate percentages occur also in core sections of Ohgocene and 

 Miocene age (Arrhenius, 1952, pis. 2.53 and 2.57; EmiUani, 1956). These varia- 

 tions do not seem to be periodic and do not correlate with the temperatures, 

 which remained more or less constant. Their cause is unknown. 



Important, apparently cyclic carbonate variations occur in at least three 

 (nos. 58, 59 and 60) of a suite of five eastern-equatorial-Pacific cores described 

 by Arrhenius (1952). These variations are believed to result from productivity 

 changes in the absence of important changes in the rate of sedimentation of the 

 non-carbonate comj)onent, and, therefore, to be inversely related to temperature 

 (Arrhenius, 1952). It is not entirely clear whether this is exactly the case or not, 

 because the carbonate percentage of the modern sediment (shown by two short 

 pilot cores) is actually closer to the carbonate maxima (which should represent 

 glacial conditions) rather than to the minima. In any case, the carbonate cycles 

 seem best interpreted in terms of climatic fluctuations. 



60 50 40 30 20 



TIME (10^ YEARS) 



10 



Fig. 3. Temperature decrease of Pacific bottom water measured by oxygen-isotopic 

 analysis of calcareous benthonic Foraminifera. (From Emiliani, 1954a.) 



b. The stratigraphic record 



As shown in Table IV, a general cooling of the Earth climate occurred during 

 the Tertiary, amounting to about 8°-10°C in middle latitudes. Supporting 

 evidence came from oxygen-isotopic measurements on calcareous benthonic 

 Foraminifera of Tertiary age from deep-sea cores raised in the eastern equa- 

 torial Pacific (Emiliani, 1954a). These measurements showed that the bottom 

 temperature of the Pacific Ocean decreased from about 10°C in mid-Ohgocene 

 time to about 2°C in the late Pliocene, reflecting a world-wide cooling possibly 

 caused by the Alpine orogenesis (which probably increased the Earth's albedo) 

 and representing cooling of the surface water of the polar seas by approxi- 

 mately the same amount (Fig. 3). A concomitant increase in atmospheric 

 turbulence is suggested by the observation that Pleistocene deep-sea sediments 

 in portions of the Pacific Ocean contain two to three times more wind-borne 



