Abstract
Abstract. A high-resolution parallel ocean model is set up to examine how the sill depth of the Atlantic connection affects circulation and water characteristics in the Mediterranean Basin. An analysis of the model performance, comparing model results with observations of the present-day Mediterranean, demonstrates its ability to reproduce observed water characteristics and circulation (including deep water formation). A series of experiments with different sill depths in the Atlantic–Mediterranean connection is used to assess the sensitivity of Mediterranean circulation and water characteristics to sill depth. Basin-averaged water salinity and, to a lesser degree, temperature rise when the sill depth is shallower and exchange with the Atlantic is lower. Lateral and interbasinal differences in the Mediterranean are, however, largely unchanged. The strength of the upper overturning cell in the western basin is proportional to the magnitude of the exchange with the Atlantic, and hence to sill depth. Overturning in the eastern basin and deep water formation in both basins, on the contrary, are little affected by the sill depth. The model results are used to interpret the sedimentary record of the Late Miocene preceding and during the Messinian Salinity Crisis. In the western basin, a correlation exists between sill depth and rate of refreshment of deep water. On the other hand, because sill depth has little effect on the overturning and deep water formation in the eastern basin, the model results do not support the notion that restriction of the Atlantic–Mediterranean connection may cause lower oxygenation of deep water in the eastern basin. However, this discrepancy may be due to simplifications in the surface forcing and the use of a bathymetry different from that in the Late Miocene. We also tentatively conclude that blocked outflow, as found in experiments with a sill depth ≤10 m, is a plausible scenario for the second stage of the Messinian Salinity Crisis during which halite was rapidly accumulated in the Mediterranean. With the model setup and experiments, a basis has been established for future work on the sensitivity of Mediterranean circulation to changes in (palaeo-)bathymetry and external forcings.
Highlights
Ever since the closure of the connection to the Indian Ocean in the Middle Miocene, water exchange between the Mediterranean Sea and the global ocean has been through one or multiple gateways in the Gibraltar arc (e.g. Dercourt et al, 2000)
The purpose of this study is to examine with a highresolution ocean circulation model how sill depth of the Atlantic connection, influenced by long-term tectonics, affects circulation and water characteristics in the Mediterranean Basin
The results of a reference experiment, with idealized surface forcing and the sill depth of the Atlantic gateway set to the present-day depth of 300 m, will be compared with observations on the present-day Mediterranean
Summary
Ever since the closure of the connection to the Indian Ocean in the Middle Miocene, water exchange between the Mediterranean Sea and the global ocean has been through one or multiple gateways in the Gibraltar arc (e.g. Dercourt et al, 2000). In the Mediterranean, the water loss by evaporation exceeds, on an annual basis, the fresh water input from precipitation and river input. The resulting fresh water deficit, i.e. evaporation – precipitation – river input, is compensated for by a net inflow from the Atlantic. Without a connection to the global ocean, the deficit would not be replenished and Mediterranean sea level would rapidly drop (Meijer and Krijgsman, 2005). The fresh water deficit in combination with the relatively small connection to the Atlantic results in a higher salinity in the Mediterranean than in the Atlantic.
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