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Over the Early–Middle Frasnian boundary interval (Late Devonian), the oceans experienced major changes in global carbon cycling and nutrient dynamics with a prominent positive carbon isotope shift at the base of the Palmatolepis punctata Zone (Middle Frasnian). The aim of this study was to construct seawater ⁸⁷Sr/⁸⁶Sr ratio curves for the Pa. transitans–Pa. hassi zonal interval using well-preserved conodont apatite from two sections in the Holy Cross Mountains, south-central Poland. The final curves suggest that seawater ⁸⁷Sr/⁸⁶Sr values were steady at ~0.70794–0.70799 during the transitans Zone but began to rise in the early punctata Zone towards a value of ~0.70814 in the late punctata Zone (an increase of ~0.0002). The increase in seawater ⁸⁷Sr/⁸⁶Sr values over the Early–Middle Frasnian boundary appears to be the second of two prominent short-term rises in ⁸⁷Sr/⁸⁶Sr values, which led to an …