1.5 r 



f 

 1/f 



Figure 31. — Spectra of climatic variations in 8 1S record in deep- 

 sea core RC 13-229 from the South Atlantic (25 °S, 

 11°E). High- resolution spectra are expressed as the 

 natural log of the variance as a function of frequency 

 (cycles per thousand years). Arrows point to spectral 

 peaks with cycle lengths of 100,000 years, 43,000 

 years, 23,000 years and 19,000 years, which are 

 similar to periods of orbital parameters. C.I. = con- 

 fidence interval. P = power or variance. K = 1,000 

 years. 



A paleothermometer that illustrates the principle involved in transforming fossil sediments into estimates of sea-surface 

 temperature Fossil microorganisms, such as the species of foraminifera shown, live near the ocean surface, then die, sink, 

 and concentrate in bottom sediments. When large numbers of a certain species are found in a sediment layer, this indicates 

 a particular surface temperature, favorable to their growth. 



49 



