EAPS Department Lecture Series - Gianmaria Sannino (ENEA)
Modelling the strait dynamics in regional climate models: recent progress, current challenges and future direction for Gibraltar-Mediterranean Sea
Since ancient times the narrow and shallow Strait of Gibraltar has fascinated and captured mankind’s imagination: for a long period of time the Pillars of Heracles - the Rock of Gibraltar to the north and Mount Hacho to the south - were thought to be the extreme edges of the Earth.
Most probably the first oceanographic definition of the Strait of Gibraltar is to ascribe to Horatius who wrote: (Roma) horrenda late nomen in ultimas extendat oras, qua medius liquor secernit Europem ab Afro, qua tumidus rigat arva Nilus…” In this Ode (23 B.C.), Horatius describes the Strait of Gibraltar as the place where the midway water separates Europe from Africa.
From a geological point of view, about five million years ago, during the Miocene, the strait was topographically blocked. This caused the desiccation of the Mediterranean, giving rise to the so-called Messinian Salinity Crisis characterised by a dramatic drop in sea level, estimated to be up to 1500 m below the current sea level. The reopening of the Strait of Gibraltar in the early Pliocene, probably due to regressive erosion, has made it possible to restore the water exchange between the Atlantic and the Mediterranean. Since then, the Strait of Gibraltar is the only dynamically significant connection between the Mediterranean and the global ocean. Through the Strait, the Mediterranean Sea exchanges water, salt and heat with the Atlantic, influencing the sea level in the basin through hydraulic controls. Long-term variability in these transports may be indicative of changes in the interior of the Mediterranean basin. On shorter time scale, the water exchange between the Mediterranean and the Atlantic Ocean is significantly affected by tidal forcing. The relevance of such effect has been recently acknowledged as one of the largest in determining the evolution of the Mediterranean water masses and therefore needs to be appropriately accounted for in numerical simulation of the Mediterranean circulation.
Nevertheless, tides and circulation on climate time scales have so far been treated separately, mainly due to the insufficient computational resources of most climate research laboratories, which imposed the implementation of relatively coarse spatial resolution models whose associated time step was at least two orders of magnitude larger than that needed to account for the fast barotropic tidal signal.
The aim of this talk is twofold. Firstly, to provide an overview of the Strait modelling works that have been determinant in filling the gaps left by the intrinsic simplicity of analytical solutions and the lack of long-term observational data. Secondly, to present the results of the first Mediterranean regional climate model, based on the MIT general circulation model, that explicitly resolves tides and the local-scale dynamics of the Strait of Gibraltar.
About this Series
Weekly talks given by leading thinkers in the areas of geology, geophysics, geobiology, geochemistry, atmospheric science, oceanography, climatology, and planetary science. Lectures take place on Wednesdays from 3:45pm in MIT Building 54 room 915, unless otherwise noted.