Isotope dilution mass-spectrometry can be applied to the determination of minute amounts of calcium in distilled water, deionized water and snow melts from ice sheets in Greenland and Antarctica. The amount of sample required is 20 g for snow analysis. In a 100-ml teflon beaker, 0.3 x 10/sup -7/ M of /sup 12/Ca spike in 0.06 g of dilute nitric acid is accurately weighed. Snow melt is poured directly into the beaker from the agitated sample bottle and is weighed. The mixture is evaporated to 50 mu l in a heated steel tank in which high purity nitrogen gas is streaming. Small drops of the concentrated liquid are loaded onto the tantalum filament by using a quartz micropipette. The ion source used is equipped with a specially designed single filament unit which is heated with accurately controlled electric current. This emits intensive Ca/sup +/ beams from 10/sup -10/ g of calcium salts loaded on the filament. The coefficient of variation for the peak height ratio of /sup 12/Ca to /sup 40/Ca ranges between 0.22 and 0.66% and is not affected by the coexistence of foreign substances. The degree of isotope effects is reduced to a minimum under 1% by runningmore » the mass- spectrometer under common conditions. Calcium and potassium have the isobars with the mass number of 40, but the isobar effects can be reduced to a negligible quantity by baking treatments. Snow melts contain minute amounts of silicate mineral dusts which have played impontant roles as the nucleation center for water vapor at the formation of snow flakes. So it is important that calcium added as a spike is equilibrated isotopically with that in the silicate mineral dusts. If it is not so, calcium isotopes in a salt matrix may be more easily released from the heated filament than those combined with the silicate matrix, and this will result in lower value of calcium. From the content of titanium, calcium from the silicate mineral dusts accounts for nearly 10% of total calcium in snow melts, while the remaining calcium occurs in sea salts predominantly. The concentrations of calclum are found to be 1.9 ppb in both redistilled and deionized water, 2 ppb in snow melts of West Enderby Land, Antarctica, and several ppb in those of Camp Century, Greenland. In Greenland snow strata, calcium concentrates in winter layers as well as dusty components. In both the polar regions, no appreciable variations of calcium concentration have been detected in whole year composite samples since 1750. (auth)« less