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The MagellanPlus workshop “BlackGate” addressed fundamental questions concerning the dynamic evolution of the Mediterranean–Black Sea (MBS) gateway and its palaeoenvironmental consequences. This gateway drives the Miocene–Quaternary circulation patterns in the Black Sea and governs its present status as the world's largest example of marine anoxia. The exchange history of the MBS gateway is poorly constrained because continuous Pliocene–Quaternary deposits are not exposed on land adjacent to the Black Sea or northern Aegean. Gateway exchange is controlled by climatic (glacio-eustatic-driven sea-level fluctuations) and tectonic processes in the catchment as well as tectonic propagation of the North Anatolian Fault Zone (NAFZ) in the gateway area itself. Changes in connectivity trigger dramatic palaeoenvironmental and biotic turnovers in both the Black Sea and Mediterranean domains. Drilling a Messinian to Holocene transect across the MBS gateway will recover high-amplitude records of continent-scale hydrological changes during glacial–interglacial cycles and allow us to reconstruct marine and freshwater fluxes, biological turnover events, deep biospheric processes, subsurface gradients in primary sedimentary properties, patterns and processes controlling anoxia, chemical perturbations and carbon cycling, growth and propagation of the NAFZ, the timing of land bridges for Africa and/or Asia–Europe mammal migration, and the presence or absence of water exchange during the Messinian salinity crisis. During thorough discussions at the workshop, three key sites were selected for potential drilling using a mission-specific platform (MSP): one on the Turkish margin of the Black Sea (Arkhangelsky Ridge, 400 m b.s.f., metres below the seafloor), one on the southern margin of the Sea of Marmara (North İmrali Basin, 750 m b.s.f.), and one in the Aegean (North Aegean Trough, 650 m b.s.f.). All sites target Quaternary oxic–anoxic marl–sapropel cycles. Plans include recovery of Pliocene lacustrine sediments and mixed marine–brackish Miocene sediments from the Black Sea and the Aegean. MSP drilling is required because the JOIDES Resolution cannot pass under the Bosporus bridges. The wider goals are in line with the aims and scope of the International Ocean Discovery Program (IODP) “2050 Science Framework: Exploring Earth by Scientific Ocean Drilling” and relate specifically to the strategic objectives “Earth's climate system”, “Tipping points in Earth's history”, and “Natural hazards impacting society”.

The MagellanPlus workshop "BlackGate"addressed fundamental questions concerning the dynamic evolution of the Mediterranean-Black Sea (MBS) gateway and its palaeoenvironmental consequences. This gateway drives the Miocene-Quaternary circulation patterns in the Black Sea and governs its present status as the world's largest example of marine anoxia. The exchange history of the MBS gateway is poorly constrained because continuous Pliocene-Quaternary deposits are not exposed on land adjacent to the Black Sea or northern Aegean. Gateway exchange is controlled by climatic (glacio-eustatic-driven sea-level fluctuations) and tectonic processes in the catchment as well as tectonic propagation of the North Anatolian Fault Zone (NAFZ) in the gateway area itself. Changes in connectivity trigger dramatic palaeoenvironmental and biotic turnovers in both the Black Sea and Mediterranean domains. Drilling a Messinian to Holocene transect across the MBS gateway will recover high-amplitude records of continent-scale hydrological changes during glacial-interglacial cycles and allow us to reconstruct marine and freshwater fluxes, biological turnover events, deep biospheric processes, subsurface gradients in primary sedimentary properties, patterns and processes controlling anoxia, chemical perturbations and carbon cycling, growth and propagation of the NAFZ, the timing of land bridges for Africa and/or Asia-Europe mammal migration, and the presence or absence of water exchange during the Messinian salinity crisis. During thorough discussions at the workshop, three key sites were selected for potential drilling using a mission-specific platform (MSP): one on the Turkish margin of the Black Sea (Arkhangelsky Ridge, 400mb.s.f., metres below the seafloor), one on the southern margin of the Sea of Marmara (North Imrali Basin, 750mb.s.f.), and one in the Aegean (North Aegean Trough, 650mb.s.f.). All sites target Quaternary oxic-anoxic marl-sapropel cycles. Plans include recovery of Pliocene lacustrine sediments and mixed marine-brackish Miocene sediments from the Black Sea and the Aegean. MSP drilling is required because the JOIDES Resolution cannot pass under the Bosporus bridges. The wider goals are in line with the aims and scope of the International Ocean Discovery Program (IODP) "2050 Science Framework: Exploring Earth by Scientific Ocean Drilling"and relate specifically to the strategic objectives "Earth's climate system", "Tipping points in Earth's history", and "Natural hazards impacting society".

The Dacian Basin was uniquely situated to record late Miocene hydrological changes that influenced depositional environments and faunal dispersal patterns in Central Eurasia's mega-lake Paratethys. Differences between the high strontium isotope ratio (87Sr/86Sr) of the waters from Lake Pannon and local Carpathian rivers and low 87 Sr/86Sr of the Eastern Paratethys (Black Sea ‒ Caspian Sea) allow a thorough investigation of connectivity and water fluxes in the transient Dacian Basin. We present a detailed 87Sr/86 Sr record for the Dacian Basin, which provides an exceptional record of basin connectivity from the latest Tortonian (ca. 7.7 Ma) until the early Pleistocene (ca. 1.8 Ma). Data show that a late Tortonian transgression (7.6–7.4 Ma) started with an incursion of Eastern Paratethys waters into the Dacian Basin, after which local rivers became the dominant source for the mostly freshwater environments of the early Messinian. The regional Maeotian-Pontian transitional interval (6.3–5.9 Ma) records a second incursion of Eastern Paratethys waters, but this time with an additional marine (Mediterranean) influx coinciding with a short-lived salinity incursion. During the Messinian Salinity Crisis of the Mediterranean, the Dacian Basin progressively connected with the Eastern Paratethys (5.9–5.5 Ma), after which it became restricted during the peak Mediterranean lowstand (5.5 Ma) and filled with Lake Pannon and local river water (5.5–5.3 Ma). During the Plio-Pleistocene, the Dacian Basin reconnectedwith the, at that time isolated, Black Sea, which shows similar 87Sr/86Sr as in the Last Glacial Maximum.

The late Miocene evolution of the Mediterranean Basin is characterized by major changes in connectivity, climate and tectonic activity resulting in unprecedented environmental and ecological disruptions. During the Messinian Salinity Crisis (MSC, 5.97-5.33 Ma) this culminated in most scenarios first in the precipitation of gypsum around the Mediterranean margins (Stage 1, 5.97-5.60 Ma) and subsequently > 2 km of halite on the basin floor, which formed the so-called Mediterranean Salt Giant (Stage 2, 5.60-5.55 Ma). The final MSC Stage 3, however, was characterized by a "low-salinity crisis", when a second calcium-sulfate unit (Upper Gypsum; substage 3.1, 5.55-5.42 Ma) showing (bio)geochemical evidence of substantial brine dilution and brackish biota-bearing terrigenous sediments (substage 3.2 or Lago-Mare phase, 5.42-5.33 Ma) deposited in a Mediterranean that received relatively large amounts of riverine and Paratethys-derived low-salinity waters. The transition from hypersaline evaporitic (halite) to brackish facies implies a major change in the Mediterranean’s hydrological regime. However, even after nearly 50 years of research, causes and modalities are poorly understood and the original scientific debate between a largely isolated and (partly) desiccated Mediterranean or a fully connected and filled basin is still vibrant. Here we present a comprehensive overview that brings together (chrono)stratigraphic, sedimentological, paleontological, geochemical and seismic data from all over the Mediterranean. We summarize the paleoenvironmental, paleohydrological and paleoconnectivity scenarios that arose from this cross-disciplinary dataset and we discuss arguments in favour of and against each scenario., We thank the entire SALTGIANT community for many profitable workshops that inspired the development of this manuscript. This research was supported by the project SALTGIANT-Understanding the Mediterranean Salt Giant, a European project which has received funding from the European Union's Horizon 2020 research and innovation program, under the Marie Sklodowska-Curie [grant agreement No 765256