An estimation of calcium carbonate deposition rate in a planktonic foraminifer Globigerinoides sacculifer using 45 Ca as a tracer; a recommended procedure for improved accuracy

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Abstract
The amount of calcium carbonate deposited in the shell of G. sacculifer during new chamber addition was assessed using 45Ca as a tracer. An improved method is recommended based on the observation that chambers formed during the first 24 h in the labeled seawater medium yield a lower estimate of total calcium carbonate deposited compared to chambers added during the subsequent 24 h intervals. The latter values, agree substantially with estimates based on laboratory measurements of shell weights from plankton samples. Based on 45Ca incorporation after the first 24 h period in the labeled medium, the mean weight of CaCO3 deposited per new chamber was 12.8 .mu.g for organisms with an initial mean length of 457 .mu.m and mean chamber growth of 166 .mu.m; and 20.8 .mu.g for larger organisms with an initial mean length of 519 .mu.m and mean chamber growth of 211 .mu.m. Some hypothetical causes for this enhanced accuracy after the first 24 h in the labeled medium are discussed and guidelines for obtaining improved estimates of calcification using 45Ca as an isotopic tracer are presented.