The Skeleton of the Mediterranean Sea

The Mediterranean Sea is of great and manifold relevance for global oceanic circulation and climate: Mediterranean waters profoundly affect the salinity of the North Atlantic Ocean and hence the global ocean circulation. Ocean motions are forced fundamentally by the atmosphere. However, direct atmospheric forcing explains just a part of the observed Mediterranean circulation, for example, the former is not able to account for the observed north-south inclination of the sea level, one of the most prominent and persistent features of Mediterranean oceanography. This implies that a significant part of this circulation feature is caused by mechanisms that are all internal, “intrinsic” to the ocean. Yet, no effort has been made so far to disentangle intrinsic oceanic phenomena from atmospherically forced ones in the Mediterranean Sea. Here, we start filling this gap of knowledge. We demonstrate that a conspicuous part of the observed Mediterranean mean state and variability belongs to a skeleton captured for the first time by a multi-centennial ocean simulation without atmospheric forcing. This study paves the way to the identification and comprehension of further observed mean patterns and low-frequency fluctuations in the Mediterranean Sea as the result of intrinsic oceanic processes rather than by a direct effect of the atmospheric forcing and could be extended to other basins where geometry and hydrological structure significantly contribute to shaping the local dynamics.