10 



GOLDBERG 



Table II 



[chap. 1 



The Residence Times of the Elements in Sea-Water as Calculated by 

 River Input and Sedimentation 



a This value was obtained from the influx value given by Barth (1952) and the amount 

 of silicon in the oceans from Table I. Barth gives only an upper limit for this latter number. 



In spite of this drastically oversimplified model of the oceans there is a 

 remarkable agreement between these two sets of data (Table II). The figures 

 span a time range of six orders of magnitude — sodium with 2.6 x 10 8 years to 

 aluminum with 100 years. At this point it should be noted that one further 

 consideration must be met in the utilization of. these results. Both A and 

 dA/dt can not have changed in times of the order of St. Even in the case of 

 sodium this assumption appears to be valid, for about 10 9 years as the age of 

 the oceans agrees with present-day geological evidence. 



The elements with long residence times, the alkali metals and alkaline earths 

 (excluding beryllium) are characterized by a lack of reactivity in the marine 

 environment. The decrease in residence times of the alkali metals with in- 

 creasing atomic number, going from sodium to cesium, reflects most probably 

 their involvement in ion-exchange equilibria with the clay minerals on the sea 

 floor, reactions proposed by Grim (1953) to regulate primarily their oceanic 

 concentrations. For positively charged monovalent ions, retention by the clay 

 phases increases with increasing radius (i.e. atomic number). Thus the sequen- 

 tial decrease in residence times of these elements is in accord with their known 

 aqueous chemical behavior. 



On the other hand, elements such as Be, Al, Ti, Cr, Fe, Nb and Th have 

 residence times under 1000 years, periods of the order of or less than the mixing 

 times for oceanic water-masses. These elements in part enter the oceans as 

 particulate phases from the continents or from volcanic activity (i.e. the clay 

 minerals, feldspars, augite, volcanic glasses, magnetite, etc. which rapidly 

 settle to the sedimentary deposits). Further, some of these elements, Al, Ti and 

 Fe, are reactants in the formation of such authigenic substances as the ferro- 

 manganese minerals, zeolites, glauconites, etc. Thus, their entry into the 

 oceans as solids and/or their high chemical reactivity matches their short 

 residence times. 



