The strontium-calcium atom ratio in carbonate-secreting marine organisms 27 



Strontium and calcium carbonates had identical solubility products of 5x10 ' in 

 sea water at a temperature of 20" C and a salinity of 35 .^ (Wattenberg and 



TiMMERMANN, 1938). 



BoGGiLD (1930) Stated that ecological variations are not effective on the form of 

 calcium carbonate in marine organisms. Odum (1951 b) and Kulp, et a/. (1952) 

 have also concluded that the sea water temperature is not an important factor in 

 determining the chemical composition of calcareous skeletons. However, Lowen- 

 STAM (1954 b) demonstrated that the environmental factors, principally temperature, 

 greatly influence the mineralogical properties of calcium carbonate in some marine 

 organisms. 



The data obtained by the authors (see Table 1) showed that some types of marine 

 organisms collected from arctic to tropical oceans always consisted of a nearly 

 constant strontium-calcium atom ratio in their calcareous shells regardless of the 

 water temperature of the environment. 



3. Salinity: In their studies of strontium in fossils and limestones, Kulp, et al. 

 (1952) stated that " the primary factor which determines strontium-calcium ratio in 

 the shell or limestone is the strontium-calcium ratio of the water from which these are 

 deposited. The strontium-calcium ratio of the water in turn is related to the salinity 

 and the source." Odum (1951 b), who used artificial sea waters of varying strontium- 

 calcium atom ratios, demonstrated that this ratio in the calcareous shell of Physa is 

 directly proportional to that of artificial sea water. He also reported an atom ratio 

 of 9-23 X 10-^ for the Atlantic Ocean water. Later investigations by Chow and 

 Thompson (1955 a and b) showed that samples of sea water collected from various 

 oceans have a constant ratio between strontium and chlorinity, and calcium and 

 chlorinity. Thus, the strontium-calcium atom ratio would be a constant (8-9 x 10^') 

 regardless of the salinity of ocean waters. From these findings and the experiments 

 of Odum (1951 b), it may be concluded that dilution or concentration of sea water 

 within the tolerance of marine organisms would not be an influential factor on the 

 strontium-calcium atom ratio of calcareous skeletons. 



Mineralogical Aspects 



Noll (1934) concluded from his investigations that there is always more strontium 

 associated with aragonite limestones than with calcite limestones. Kulp, et al. (1952) 

 substantiated this by stating that calcite has a crystal lattice which is less amenable 

 to strontium than the aragonite lattice. Vinogradov (1953) implied that Noll's 

 rule cannot be applied strictly to calcareous shells of marine organisms, but that the 

 rule is valid, in general, for many of them. 



The analytical results obtained by the present authors together with the mineral- 

 ogical data secured by previous investigators are summarized in Table VI. The 

 majority of the specimens studied apparently had calcium carbonate existing as calcite- 

 The calcite group includes Algae (Corallinaceae), Protozoa (Foraminifera), Porifera 

 (Calcarea), Coelenterata (Alcyonaria), Arthropoda(Cirripedia), Mollusca (Anomiidae, 

 Ostreidae and Pectinidae of Pelecypoda), Bryozoa, Brachiopoda (Articulata) and 

 Echinodermata. The average strontium-calcium atom ratio of this group ranged from 

 1-22 to 4-45 X 10-^ In phylum Mollusca, the Pelecypoda (except three families 

 mentioned above) and the Gastropoda (Prosobranchia) had a calcite-aragonitc 



