LAUSR

ABSTRACT Karst springs in the Main Range of the Crimean Mountains and the Crimean Piedmont show a restricted range of values (δ18O = –10.5 to –8.0 ‰, δ2H = –72 to –58 ‰), somewhat more negative than the weighted mean of meteoric precipitation. This suggests preferential recharge at higher elevations during winter months. Groundwater tapped by boreholes splits in three groups. A first group has isotopic properties similar to those of the springs. The second group shows significantly lower values (δ18O = –13.3 to –12.0 ‰, δ2H = –95 to –82 ‰), suggesting recharge during colder Pleistocene times. The third group has high isotope values (δ18O = –2.5 to +1.0 ‰, δ2H = –24 to –22 ‰); the data points are shifted to the right of the Local Meteoric Water Line, suggesting water–rock exchange processes in the aquifer. These boreholes are located in the Crimean Plains and discharge mineralized (ca. 25 g L−1) thermal (65°C) water from a depth of 1600–1800 m. Groundwater associated with mud volcanoes on the Kerch peninsula have distinct isotope characteristics (δ18O = –1.6 to +9.4 ‰, δ2H = –30 to –18 ‰). Restricted δ2H variability along with variable and high δ18O values suggest water–rock interactions at temperatures exceeding 95 °C.