132 



HISTORY OF THE OCEANS 



which are concentrated by the biological processes at the equator 

 and which do not to the same extent as the major biogenous 

 sedimentary component, calcite, suffer from dissolution (Fig. 2, 

 top graph). These rates can be expressed in relative units as mass 

 of the biologically concentrated component per unit mass of 

 inorganic deposit. As a convenient measure of the latter have been 

 employed elements like aluminum or titanium in such remote and 

 protected basins where evidence for a reasonably low variability in 

 the contribution of inorganic components has been obtained. In 

 Fig. 3 are plotted the results by Goldberg on the rate of accumu- 

 lation of barium In the Postglacial stratum in the east Pacific as a 

 function of latitude, showing a sharp maximum under the equator 

 with about twenty-five times the rate prevailing at higher latitudes, 

 and a drop to 1/e of the maximum value at a distance of about 

 l}y<2 degrees north and south of the equator. The rare earth elements 

 and zirconium are still more promising than barium in this respect, 

 as they are laid down in the form of highly insoluble phosphates 

 which do not appear to migrate In the sediment. 



In the sedimentary sequence available at the equator by present 

 coring methods we do not reach further back in time than to the 

 Middle Pleistocene, or roughly half a million years. During this 

 time, the pole has remained constant within the resolution of the 

 present sampling grid which is about four degrees of latitude. A 

 500-m long core in the equatorial sediment bulge would probably 

 take us back at least into Middle Cretaceous strata, and to a time 



BaO 

 TiO, 



0" 5' 



Latitude 



IS'N 



Fig. 3. Relative rate of accumulation of barium in the Postglacial stratum of 

 the profile shown in Fig. 2 (Goldberg and Arrhenius, 1958). 



