The Sr⁸⁷/Sr⁸⁶ ratios of calcium carbonate in cores 1474P and 1445P from the Black Sea vary significantly as a function of depth from average values of 0.7095 ± 0.0003 at the top of the cores to 0.7073 ± 0.0003 between depths of about 70 and 1,158 cm. The calcium carbonate fraction of the postglacial sediment at the top of the cores consists primarily of coccoliths of the contemporary marine species Emiliania huxleyi (Lohman). Below a depth of about 70 cm, the sediment was deposited in fresh to brackish water during the Wurm glaciation; that sediment contains redeposited coccoliths of species which became extinct in Late Cretaceous to early Tertiary time. The Sr⁸⁷/Sr⁸⁶ ratios of the calcium carbonate fracti n of the sediment therefore indirectly reflect the change in the environment of deposition which occurred at the end of the Wurm glaciation when the Black Sea was reconnected with the Mediterranean Sea as a result of the eustatic rise of sea level. An anomaly was discovered in sample 1474P (800 cm), which contains calcium carbonate having a Sr⁸⁷/Sr⁸⁶ ratio of 0.7090 ± 0.0002. Water from station 1468 (35 cm) in the Black Sea has a Sr⁸⁷/Sr⁸⁶ ratio of 0.7093 ± 0.0007 (one standard deviation).