The Messinian Salinity Crisis

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In 1970, an undersea drilling project began taking samples of the Mediterranean’s ocean floor. They discovered an area of salt up to 3 kilometers thick and located 100-200 meters below the ocean floor, which they named the M-reflector. By studying the salt, they found that the Mediterranean Sea must have dried up at one point millions of years ago for an extensive period of time.


They called this drying of the Sea the Mediterranean Salinity Crisis (MSC).  The MSC began approximately 6 million years ago (MYA) and lasted until around 5.3 MYA – a time span of well over a half million years!  Although scientists are still not completely sure about the cause of the MSC, they do have evidence that offers some explanations. 


For example, there is strong evidence that the sea level had dropped about 70 meters (over 200 feet) prior to the Crisis.  Scientists believe that this was due to a cooling of the globe.  Global cooling would allow water to freeze and form glaciers & icebergs. A large amount of this water would come from the ocean, simply because the ocean has a lot more water than any other place on Earth.  With less water, the ocean’s sea level would drop. 


This drop in sea level made it difficult for the Atlantic Ocean to flow into the Mediterranean, and the Mediterranean began receiving a much lower amount of water.  The Mediterranean tends to evaporate at a very fast pace, because it is located in a dry area.  Note that it is located just to the north of the Sahara Desert, which is one of the driest places on Earth.  Therefore, the Mediterranean is very vulnerable to drying up if it does not receive enough water.


Meanwhile, the ocean floor beneath where the Atlantic Ocean was connected to the Mediterranean began to rise.  Southwestern Europe and northwestern Africa had been moving towards each other.  This forced the area between the 2 continents to rise because there was no where else for that area to move.  Scientists believe that by 5.59 MYA, the ocean floor had been raised high enough to become an area of land that completely separated the Mediterranean from the Atlantic Ocean.  This must have caused the Mediterranean’s sea level to drop even more quickly, because at this point the Mediterranean was completely isolated from the Atlantic Ocean. 


As the water in the Mediterranean evaporated, the salt that was in the water was left behind and began to build up in layers on the floor of the Mediterranean.  Two major salts that were deposited on the floor were Halite and Gypsum.  Some of the salt deposit areas were 800 meters (2,500 feet) deep! 


However, the salt in the Mediterranean did not deposit on the floor as quickly as the water was evaporating.  This means that whatever water was left in the Mediterranean became very salty.  This high amount of salt in the water (also known as salinity) caused the Mediterranean to become deadly to all marine life.  The Mediterranean continued to dry up until there was almost no water left.  At this point, the Mediterranean must have been a gigantic basin with a depth comparable to that of the Grand Canyon, which on average is about 1,600 meters (5,000 feet) deep.


Finally, at around 5.33 MYA, the connection between the Mediterranean and Atlantic Ocean was reopened. The cause of this reopening is still unclear, but again there are some possible explanations.


First, when the Mediterranean was drying out, the amount water that evaporated was enough to cause an average rise in sea level of 10 meters (33 feet).  In other words, the water that had evaporated from the Mediterranean was eventually able to reach the oceans when it fell as rain or snow.  This would have allowed the Atlantic Ocean to creep back towards the Mediterranean. 


In addition, there is evidence that a lot of erosion took place during the time when the Mediterranean was cut off from the Atlantic Ocean on the relatively small area of land that divided the two bodies of water.  The main cause of this erosion was probably caused by wind and rainwater that plunged down the slope on the western side of the Mediterranean basin.  As more land was eroded away, the area that separated the Atlantic Ocean and Mediterranean became weaker and made it easier for the Atlantic Ocean to force its way into the Mediterranean.


After the basin was refilled, the Mediterranean Sea returned to what it is today.