The role of gateways in the evolution of temperature and salinity of semi-enclosed basins: An oceanic box model for the Miocene Mediterranean Sea and Paratethys

Marine gateways are important for semi-enclosed basins as they control exchange flows and influence water circulation. During much of the Early and Middle Miocene (~23–13Ma), the Paratethys (of which at present only the Black Sea and Caspian Sea remain) and the Mediterranean Sea were connected to both the Atlantic and Indian Oceans. The gateways to the Indian Ocean were closed ultimately in the Middle Miocene. Here, we apply an oceanic 4-box model to determine the temperature, salinity and exchange flows for the Paratethys and the Mediterranean Sea before and after closure of the Indian Ocean gateways. Our analysis forms a novel way of linking tectonics, climate and basin evolution. We investigate whether changes observed in the geological record of Paratethys are caused by changes in gateway configuration or in climate. We mainly focus on Paratethys which, because of the availability of a large variety of geological studies, presents an outstanding opportunity for studying the evolution of semi-enclosed basins and the impact of gateway closure. Moreover, Paratethys is considered to have played an important role in the evolution of Eurasian climate. Our analysis explores various values of the model parameters such as net evaporation and surface heat flux. Our main conclusions are: (1) Paratethys became more responsive to climate change after closure, (2) closure of the gateways to the Indian Ocean probably caused cooling of Paratethys and, in particular, accounted for the enigmatic Mid-Burdigalian cooling in Paratethys, (3) closure induced a change in salinity of Paratethys which is dependent on the net evaporation and size of the gateway connecting Paratethys to the Mediterranean, (4) Paratethys is sensitive to closure of both the gateway between Paratethys and the Indian Ocean, and the gateway between the Mediterranean Sea and the Indian Ocean, (5) Paratethys is influenced by the water properties of the Mediterranean Sea, (6) the water properties of Paratethys have only very limited influence on the Mediterranean Sea, and (7) in the advanced stage of the closure, the Mediterranean/Paratethyan temperature and salinity became more responsive to the restriction of the eastern gateways.