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The Messinian Salinity Crisis (MSC) successions record extreme fluctuations in the Mediterranean’s environmental conditions. However, some of the scenarios that are thought to have caused these extreme environments are contentious. One prominent example of this is the Mediterranean water level during the Lago-Mare stage of the MSC, which is interpreted either as being very low during a largely desiccated Mediterranean punctuated by endorheic lakes (lacustrine scenario) or sufficiently high to enable basin-wide connectivity across the Mediterranean and with the Atlantic and the Eastern Paratethys (lagoonal scenario). In SE Spain, adjoining marginal basins of Sorbas, Nijar and Vera exhibit sedimentary records of the Lago-Mare stage. Here we present 11 new 87Sr/86Sr isotope ratios measured on ostracod (Cyprideis sp.) valves from these successions, which add to the 11 already published data from these basins and whose significance, in terms of water provenance, has not been fully explored. In parallel, we construct a mass balance model that provides quantitative insights into the Sr isotopic composition of the water in which the ostracods dwelt. Overall, measured and published 87Sr/86Sr isotope ratios from Sorbas (0.709066–0.709131), Nijar (0.708814–0.709099) and Vera (0.708764–0.708813) all show lower values than modelled ratios for endorheic lakes (>0.7100). These Spanish basins therefore require an additional source of water with a lower Sr isotope signature which is likely to have been derived from the main Mediterranean waterbody (0.7086–0.7087). This interpretation implies that at least the Western Mediterranean had a relatively high and fluctuating water level during the Lago-Mare stage of the MSC.

The Messinian Salinity Crisis (MSC) successions record extreme fluctuations in the Mediterranean's environmental conditions. However, some of the scenarios that are thought to have caused these extreme environments are contentious. One prominent example of this is the Mediterranean water level during the Lago-Mare stage of the MSC, which is interpreted either as being very low during a largely desiccated Mediterranean punctuated by endorheic lakes (lacustrine scenario) or sufficiently high to enable basin-wide connectivity across the Mediterranean and with the Atlantic and the Eastern Paratethys (lagoonal scenario). In SE Spain, adjoining marginal basins of Sorbas, Nijar and Vera exhibit sedimentary records of the Lago-Mare stage. Here we present 11 new 87Sr/86Sr isotope ratios measured on ostracod (Cyprideis sp.) valves from these successions, which add to the 11 already published data from these basins and whose significance, in terms of water provenance, has not been fully explored. In parallel, we construct a mass balance model that provides quantitative insights into the Sr isotopic composition of the water in which the ostracods dwelt. Overall, measured and published 87Sr/86Sr isotope ratios from Sorbas (0.709066–0.709131), Nijar (0.708814–0.709099) and Vera (0.708764–0.708813) all show lower values than modelled ratios for endorheic lakes (>0.7100). These Spanish basins therefore require an additional source of water with a lower Sr isotope signature which is likely to have been derived from the main Mediterranean waterbody (0.7086–0.7087). This interpretation implies that at least the Western Mediterranean had a relatively high and fluctuating water level during the Lago-Mare stage of the MSC.