The skeleton of the Mediterranean Sea

The atmosphere forces oceanic motions. However, direct atmospheric forcing is not able to explain several observed features of the mean Mediterranean circulation like, for instance, the large-scale meridional sea level inclination, a strong and persistent feature of the Mediterranean oceanography. Low-frequency changes in the Mediterranean Sea have also been observed that cannot be explained by a mere response of the ocean to atmospheric changes. However, model studies of the intrinsic mean state and variability of the Mediterranean Sea appear to be lacking.

Here, we start filling this gap of knowledge. We demonstrate [1] 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. An eddy-permitting nonlinear, shallow-water multilayer numerical model was only forced by steady transports of Atlantic Water and Levantine Intermediate Water at its western and eastern open boundaries located along meridional sections crossing the strait of Gibraltar and the Levantine basin, respectively. The lack of any atmospheric forcing is very peculiar of our approach and is crucial for revealing the intrinsic mean state.

Comparison of the simulated annual mean surface displacement with the corresponding absolute dynamic topography altimetric data for the period 1993–2020 provided by the Copernicus Climate Data Store, yields large patterns of coherent correlation -including a large-scale meridional sea level inclination- that are clearly all of intrinsic origin. This result paves the way to the recognition of a noticeable contribution exerted by intrinsic oceanic mechanisms to the sea level rise observed in recent years over the Mediterranean Sea. In addition, a strong and previously unknown intrinsic oceanic variability appears, which contributes to explaining a conspicuous part of the poorly understood observed interior low-frequency oceanic variability.

[1] Rubino A, S. Pierini, S. Rubinetti, M. Gnesotto and D. Zanchettin, 2023: The skeleton of the Mediterranean Sea. J. Mar. Sci. Eng., 11, 2098; https://doi.org/10.3390/jmse11112098.