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.
