The strontium-calcium atom ratio in carbonate-secreting marine organisms 21 



STAM (1954 A and b) dealt with the effect of environmental factors upon the mineral- 

 ogical character of the calcium carbonate in certain marine organisms. 



Strontium has been detected in all phases of the biosphere. Due to the difficulty 

 in analyzing trace quantities of strontium in the presence of calcium., only a few 

 scattered analyses were reported in the early literature showing the existence of 

 strontium in marine organisms (MoRETTi, 1813; Vogel, 1814; Forchhammer, 1852; 

 DiEULAFAiT, 1877; ScHMELCK, 1901). More recently, the role of strontium in the 

 carbonate-secreting marine organisms has been the object of investigation, and 

 several quantitative determinations were made on the distribution of strontium in 

 various biological materials (Fox and Ramage, 1931; Noll, 1934; McCance and 

 Masters, 1937; Webb, 1937; Trueman, 1944; Tsuchiya, 1944, 1948; Vinogradov 

 and Borovik-Romanova, 1945; Asari, 1950; Odum, 1951 a). The relationship 

 between the strontium content of fossils and that of recent marine organisms has also 

 been studied (Odum. 1951 b; Kulp, et ah, 1952). 



In summarizing the work of previous investigators, it may be said that strontium 

 was found not only in the calcareous shells, but also in the tissues of marine organisms. 

 It was also stated by some that the primary factor which determines the strontium- 

 calcium atom ratio in the calcareous skeletons is the atom ratio of these elements 

 occurring in the water in which the organisms lived. Experiments showed that large 

 quantities of strontium could be taken into the calcareous shells of marine organisms 

 grown under controlled conditions and that the relationship between the strontium- 

 calcium atom ratio in the shells is almost directly proportional to the atom ratio of 

 the environment. Since the strontium-calcium atom ratio in the calcareous skeletons 

 reflects the chemical composition of the water, the analysis of the strontium-calcium 

 atom ratio in unaltered fossils could be used as a valid method of measuring the 

 strontium-calcium ratio of the ancient oceans. Such findings presented strong evidence 

 that the strontium-calcium atom ratio of ocean waters has been of about the same 

 order of magnitude since Palaeozoic times at least, because this atom ratio of the 

 fossils resembles that of the modern counterparts. 



In marine organisms the strontium-calcium atom ratio of the growing shells is 

 apparently independent of the age of the organisms. No evidence was found that 

 would indicate any seasonal fluctuations in the strontium-calcium atom ratio of 

 marine organisms. It was also concluded that the temperature of the ocean waters is 

 a relatively insignificant factor in aff'ecting the strontium content of marine organisms. 



Besides the chemical composition and the ecological environment, the mineralogical 

 character, such as crystal lattice, of the calcareous skeletons was of some significance. 

 It was found that there is always more strontium present when the calcium carbonate 

 exists as aragonite rather than as calcite. 



METHODS OF ANALYSIS 



All chemicals used in the present investigation were of analytical grade and tested for traces of 

 strontium and calcium. A stock solution of strontium, 6 00 mg-atoms per litre, was prepared by 

 dissolving 0-886 gram of strontium carbonate in a limited volume of hydrochloric acid and then 

 diluting to one litre; and that of calcium. 200 mg-atoms per litre, was prepared by d.ssolvmg 2 002 

 grams of calcium carbonate in hydrochloric acid and diluting to one litre. From such stock solutions, 

 suitable aliquots were taken and diluted for the comparison standards. Polyethylene containers were 

 used for storage of standard solutions in order to avoid possible contamination from the glassware. 



The calcareous skeletons of the marine organisms were carefully cleaned and air-dried. Duplicate 



