Papers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep-Sea Research, pp. 20-. 39 



The strontium-calcium atom ratio in carbonate-secreting marine 



organisms 



By Thomas G. Thompson and Tsaihwa J. Chow 

 Department of Oceanography, University of Washington 



Summary — The purpose of the present investigation was to study the distribution of strontium and 

 calcium in the biosphere. The contents of strontium and calcium in 250 species of carbonate-secreting 

 marine organisms were determined. The strontium-calcium atom ratio in calcareous portions of 

 marine organisms ranged from 1-0 to 11 x 10"^. With the exception of Nudibranchia and Madre- 

 poraria, the atom ratio in marine organisms was less than that of sea water, 8 -9 x 10"*. The strontium- 

 calcium atom ratios in marine organisms appeared to be constant in accordance with their phylo- 

 genetic classification. Specimens of different species collected from a common ecological community 

 showed diverse strontium-calcium atom ratios. On the other hand, the similar types of marine 

 organisms living under different environmental conditions from arctic to tropical oceans, showed 

 constant strontium-calcium atom ratios. Variations in salinity and temperature of sea water were 

 apparently not the factors which influenced the strontium-calcium atom ratio in calcareous shells. 



The mineralogical properties of calcium carbonate in marine organisms demonstrated a definite 

 correlation with the occurrence of strontium. The marine organisms containing calcium carbonate 

 as aragonite had strontium-calcium atom ratios greater than those as calcite. Samples of deep-sea 

 sediments and Clobigerina ooze showed strontium-calcium atom ratios of 1 -94 x 10~* and 1 -49 x 10~*, 

 respectively. The limestone deposits, which originated from marine organisms, had the smallest 

 strontium-calcium atom ratio, 0-63 x 10"*, of all materials examined. Apparently, the matrix of 

 calcareous deposits of marine origin has lost strontium during geological time. 



INTRODUCTION 



The present investigation was undertaken in order to study (1) the distribution of 

 strontium in the carbonate-secreting marine organisms, (2) to ascertain possible 

 correlations between the strontium and calcium contents of the calcareous skeletons, 

 (3) to observe variations of the strontium-calcium atom ratio in accordance with the 

 phylogeny of the marine organisms, (4) to note the extent of change in the atom ratio 

 of marine organisms living in different natural environments, and (5) to determine the 

 strontium content in relation to the mineralogical character of the calcium carbonate 

 in the organisms. 



The determination of small quantities of strontium in the presence of large amounts 

 of calcium has been rather a laborious process. However, both of these elements can 

 be determined readily by flame photometric methods recently described by Chow and 

 Thompson (1955 a and b). 



REVIEW OF LITERATURE 



The occurrence of calcium in marine organisms has been studied extensively, as it 

 is the major constituent of many skeletal remains in calcareous marine sediments. 

 An authoritative summary and discussion on the distribution of calcium in marine 

 organisms has been presented by Vinogradov (1953). The investigations of Lowen- 



Contribution from the Department of Oceanography, University of Washington. Publication 



No. 184. 



20 



