Stage 20: Marseille

The penultimate stage is an individual time trial in this year’s Tour de France, and it takes us through the streets of Marseille along the Mediterranean Sea, so it’s our last chance this year to take a look at Mare Nostrum.

Port_Autonome_de_Marseille

The Port of Marseille and the Mediterranean Sea.

The Mediterranean Sea has a fascinating geological history. Formed by the tectonic motion of the African and Eurasian plates, the connection between the basin and the Atlantic Ocean closed off some 6 million years ago. In the warm climate and without continual flushing from the Atlantic Ocean, the sea dried up, and what little water was left was very saline. The Messinian Salinity Crisis ended when the Strait of Gibraltar was breached and water poured in from the Atlantic Ocean.

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An interpretation of the Zanclean Flood that opened the Strait of Gibraltar and flooded the Mediterranean.

Though the sea receives freshwater inputs from rivers like our old friend the Rhône, the warm and dry “Mediterranean” climate causes significant evaporation within the basin so that the Mediterranean water is significantly saltier than the Atlantic Ocean water. Atlantic water is lighter than Mediterranean water, so it sits on top of the Mediterranean water as it flows eastward. As it evaporates, it becomes heavier, sinks in the eastern part of the sea and starts to flow west where it escapes into the Atlantic through the Strait of Gibraltar. Because it’s now a lot heavier than the Atlantic water, it sinks to the bottom of the sea and travels far offshore as a fairly coherent mass.

Time trials can be very dramatic, but Geraint Thomas in Düsseldorf, the winner, Maciej Bodnar, kind of slipped under our radar until he showed up in the stadium with an impressive time and exacted his revenge for being caught on the way into Pau. The standings for all the jerseys are basically cemented now, so we can move on to the celebrations on the Champs-Élysées tomorrow night.

 

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