Model analysis of the role of marine gateways in the palaeoceanography of the Miocene Mediterranean basin and Paratethys

In the Early Miocene (23–16 Ma) the Mediterranean region was different from that at present. The Mediterranean Sea was more extensive than today and it was opened to the Indo-Pacific Ocean, to the Atlantic Ocean, and to the Paratethys—the predecessor of the Black, Caspian and Aral seas—to the north. The progressive palaeogeographic evolution of the Mediterranean region, driven by plate tectonics, resulted in the modern enclosed physiography of the Mediterranean Sea. This process includes changes in bathymetry and geometry of marine basins and marine gateways. Marine gateways are oceanic passages between neighbouring basins which allow interbasinal exchange of water, heat and salt. Opening and closure of these gateways can therefore affect the ocean circulation on the regional and (or) global-scales, with a concomitant effect on climate. Changes in ocean circulation are recorded in the marine sediments, the study of which is essential to reconstruct palaeoenvironments. However, the examination of the sedimentary record is not sufficient to determine the physical processes responsible for the environmental conditions inferred, nor to assess whether the observed conditions are applicable to the entire basin or represent a local phenomenon. In this thesis I have used several regional-scale numerical models to gain physics-based insight into the role of the marine gateways of the Miocene (23-5 Ma) Mediterranean region in the palaeoceanography of the Mediterranean and Paratethys. I address first-order features such as basin temperature and salinity, basin-scale thermohaline circulation, patterns of exchange in the gateways, and sea level. By comparing model results to geological data I am able to discard previously proposed scenarios and formulate new ones. I focus on the shoaling and closure of the gateway which used to connect the Mediterranean Sea to the Indo-Pacific until the Middle Miocene. Using a regional-scale ocean circulation model, and comparing my model results to proxy data, I determine the exchange patterns between the Mediterranean and the adjacent Atlantic and Indian oceans during the different stages of closure—some of them not considered before. I also examine the interplay of the two marine corridors that connected the Mediterranean and the Atlantic during the Late Miocene. Results obtained with a regional-scale ocean circulation model show that the exchange pattern in these corridors only depends on the relative depths of the corridors. This is useful to reconstruct the sequence of events that culminated in the deposition of evaporites in the Mediterranean during the Messinian Salinity Crisis and allows me propose new model-based scenarios as to the exchange patterns in the corridors. Finally, I perform a quantitative analysis to assess the sensitivity of the Late Miocene Paratethys sea level to hydrologic budgets when the Paratethys is isolated from the Mediterranean due to gateway closure. Comparing the model results with (i) salinity estimates inferred from the geological record and (ii) Late Miocene hydrologic budgets calculated from a global climate model simulation, I exclude a 1000 m sea level drop in the Caspian Sea during the time period investigated. In the Black Sea this cannot be completely discarded