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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.

A gigantic cascade of Atlantic waters, filling the deep desiccated Mediterranean basin at the beginning of the Pliocene, has commonly been envisaged to end the Messinian Salinity Crisis (MSC). The Mediterranean lowstand during its final “Lago-Mare” phase, however, has long been subject to major controversy and has recently been seriously questioned again. Here, we present high-resolution ostracod distribution patterns of the MSC successions in the Black Sea basin (Zheleznyi Rog section; Russia) and the Mediterranean (Cuevas del Almanzora section; Spain) to study the origin and migration history of the Lago-Mare ostracods. We conclude that two major phases of faunal migration have taken place in the Messinian. The first phase corresponds to the Maeotian–Pontian boundary interval (~ 6.1–6.0 Ma) of the Paratethys, where mainly Pannonian species suddenly invaded the Black Sea region. The second migration event corresponds to the Lago-Mare phase of the Mediterranean when first (5.55–5.47 Ma) some opportunistic taxa (species of Cyprideis and Loxoconcha genera) and then (5.40–5.33 Ma) a more diverse assemblage of Paratethyan species occupied the entire Mediterranean region. The Spanish ostracod assemblages show a high percentage of Paratethyan (Pontian) ostracods, in agreement with previously studied Italian Lago-Mare sections. The similar palaeoenvironmental changes that developed roughly synchronously in the western and central Mediterranean marginal basins provide more evidence for intrabasinal exchange at high water level during the final stage of the Lago-Mare phase. This indicates that the Mediterranean in the latest Messinian was full of water (comparable to the present Caspian Sea) and that the Zanclean deluge, if happened, only surged some tens, up to few hundred metres, into the Mediterranean.

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.