Nothing good. But still, what would happen?
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land. Although the sea is sometimes considered a part of the Atlantic Ocean, it is usually identified as a separate body of water.
Geological evidence indicates that around 5.9 million years ago, the Mediterranean was cut off from the Atlantic and was partly or completely desiccated over a period of some 600,000 years before being refilled by the Zanclean flood about 5.3 million years ago.
Did you know that there was actually a plan to build a dam at Gibraltar and partly desiccate the sea once again?