The Messinian salinity crisis (also called the Messinian event and the Lago Mare event) was a time when the Mediterranean Sea dried up partly or almost completely during the later part of the Messinian age in the Miocene epoch, from 5.96 to 5.33 million years ago. This event ended with the Zanclean flood, when the Atlantic Ocean refilled the Mediterranean Sea.
Sediment samples from beneath the deep seafloor of the Mediterranean Sea, which include salt deposits, soil, and plant fossils, show that the area where the Strait of Gibraltar is now located closed about 5.96 million years ago. This blocked the Mediterranean from connecting to the Atlantic Ocean. This closure caused the Mediterranean Sea to begin drying up, the first of several such events during the late Miocene. When the strait closed for the final time around 5.6 million years ago, the dry climate of the region caused the Mediterranean basin to nearly dry out completely within about 1,000 years. This extreme drying created a very deep, dry basin that was 3 to 5 kilometers (1.9 to 3.1 miles) below normal sea level, with some areas as salty as today’s Dead Sea. Later, around 5.5 million years ago, wetter weather brought more fresh water from rivers into the basin, slowly filling it and turning the salty lakes into brackish water, similar to today’s Caspian Sea. The crisis ended when the Strait of Gibraltar reopened about 5.33 million years ago, allowing the Atlantic Ocean to quickly refill the Mediterranean Sea in an event called the Zanclean flood.
Even today, the Mediterranean Sea is much saltier than the North Atlantic Ocean because it is nearly separated by the Strait of Gibraltar and has a high rate of water evaporation. If the Strait of Gibraltar were to close again (which is likely to happen in the future on a geological timescale), the Mediterranean Sea would mostly dry up in about 1,000 years. Continued movement of the African continent northward might eventually erase the Mediterranean Sea entirely.
Naming and first evidence
In the 19th century, Karl Mayer-Eymar, a Swiss geologist and paleontologist who lived from 1826 to 1907, studied fossils found in layers of sediment that contained gypsum, brackish water, and freshwater. He determined these fossils were deposited just before the end of the Miocene Epoch. In 1867, he named this time period the Messinian after the city of Messina in Sicily, Italy. Later, scientists discovered other layers rich in salt and gypsum across the Mediterranean region, and these layers were also dated to the same time period.
Further evidence and confirmation
In 1961, seismic surveys of the Mediterranean basin discovered a geological layer about 100–200 meters (330–660 feet) below the seafloor. This layer, called the M reflector, matched the shape of the seafloor, indicating it was formed evenly and consistently in the past. Scientists believed this layer was created by salt deposits. However, different ideas existed about when the salt was deposited and how old it was.
In 1952, Denizot and in 1967, Ruggieri suggested the layer was from the Late Miocene period. Ruggieri also introduced the term "Messinian salinity crisis" to describe this event.
In 1970, new seismic data about the M reflector was collected in the Mediterranean. At the same time, scientists drilled into the salt layer during Leg 13 of the Deep Sea Drilling Project, using the ship Glomar Challenger. William B. F. Ryan and Kenneth Hsu led the project. The salt deposits were tested and found to be related to the Messinian salinity crisis.
In the summer of 1970, geologists on the Glomar Challenger retrieved drill cores from deep parts of the Mediterranean. These cores contained gravel from dry riverbeds, red and green floodplain sediments, gypsum, anhydrite, rock salt, and other minerals that form when seawater dries up. Some samples included potash, a mineral left behind when salty water evaporated completely. One core showed layers of tiny ocean creature remains that dried into dust and were carried by windstorms. This dust mixed with sand from nearby continents and settled in a salt lake between layers of rock salt. These layers alternated with layers containing marine fossils, showing repeated cycles of drying and flooding.
The large amount of salt does not mean the sea completely dried up. Evidence of the Mediterranean’s salt buildup comes from canyons carved by rivers into the dry seabed. For example, the Nile River carved a channel 200 meters (660 feet) deep at Aswan and 2,500 meters (8,200 feet) deep near Cairo.
In many areas of the Mediterranean, cracks in ancient mud have been found, showing the mud dried and cracked under intense heat. In the Western Mediterranean, layers of ocean sediment mixed with salt deposits suggest the area was flooded and dried repeatedly over 700,000 years.
Chronology
The salinity crisis in the Mediterranean Sea began about 5.96 million years ago, as shown by ancient magnetic records from rocks that were once underwater but are now above sea level due to tectonic movements. This event is part of the "Messinian" age, which is a time in the Miocene epoch marked by changes in sea levels, tectonic activity, and the formation and erosion of rock layers.
During this time, the narrow waterway between the Mediterranean Sea and the Atlantic Ocean repeatedly closed, causing the Mediterranean Sea to dry up partially more than once. Eventually, the sea became completely isolated from the Atlantic Ocean between 5.59 and 5.33 million years ago, leading to a significant drop in sea level. In the early, very dry stages (5.6–5.5 million years ago), strong erosion created massive canyons around the Mediterranean, some as large as the Grand Canyon. Later, between 5.50 and 5.33 million years ago, salt layers formed in a large basin that was part lake and part sea, known as the "Lago Mare" event.
About 5.33 million years ago, the waterway at the Strait of Gibraltar opened again, allowing the Atlantic Ocean to flood the Mediterranean Sea in a major event called the Zanclean flood. This refilled the basin and has not dried up since.
Scientists estimate that the amount of salt deposited during the Messinian period was about 4 × 10 kg, though this number may be lower with more research. This salt suggests the Mediterranean Sea dried up multiple times or had very high salt levels for a long time. Evidence shows that the sea may have dried and refilled several times, with drying periods linked to cooler global temperatures. Each refill likely happened when a water passage opened due to tectonic shifts or rivers flowing into the Mediterranean. The final refill occurred at the start of the Pliocene epoch when the Strait of Gibraltar opened permanently.
Studies of rock layers, such as those in Hole 124, show that the oldest sediments were deposited in deep sea or brackish lake environments. As the sea level dropped, these layers became uneven due to wave action. Later, salt formations like stromatolites and anhydrite appeared as the sea dried completely. Sudden flooding from the Atlantic or brackish water from other regions would then cover these salt layers with new sediments.
Recent research suggests the desiccation and flooding cycle may have repeated multiple times during the last 630,000 years of the Miocene epoch, explaining the large salt deposits. However, other studies argue that repeated drying and flooding is unlikely based on geological evidence.
Some questions remain about the start of the crisis in the central Mediterranean. The connection between salt layers found in accessible areas like the Tabernas Desert and Sorbas Basin and those in central basins is still unclear.
Two main theories exist about salt deposition: one suggests salt layers formed at the same time in all basins, while the other claims they formed in stages, first in shallow areas and later in deeper ones.
Studies using cyclostratigraphy, which compares sediment layers to identify patterns, have found that salt deposits in the main Mediterranean basin and the Sorbas Basin in Spain appear to have formed at the same time. Supporters of this idea argue that these patterns are linked to astronomical cycles, making the timing of events more precise. Opponents, however, question this, suggesting the Sorbas Basin may have been exposed and eroded before the main basin’s salt layers formed.
Recent work highlights a major erosion event before the salt deposits formed, called the "Messinian erosional crisis." This event likely caused the Mediterranean Sea level to drop significantly before salt layers formed in central basins. Studies suggest that deep water formation was unlikely during this time, and any salt deposits in central basins may have formed under different conditions than previously thought.
Causes
Scientists have studied several possible reasons for the Messinian crises, which were a series of events that affected the Mediterranean Sea. While experts disagree on many details, most agree that changes in climate likely influenced the repeated filling and drying of the sea basins. Also, tectonic forces—movements of Earth's crust—probably controlled the height of underwater ridges that limited water flow between the Atlantic Ocean and the Mediterranean. However, the exact size and impact of these effects are still debated.
The causes of the Mediterranean Sea becoming isolated from the Atlantic Ocean are likely connected to the area now occupied by the Strait of Gibraltar. This region is where the African and European tectonic plates meet, along with smaller fragments like the Iberian plate. This boundary is marked by a curved tectonic structure called the Gibraltar Arc, which includes parts of southern Spain and northern Africa. Today, three similar curved tectonic features exist in the Mediterranean: the Gibraltar Arc, the Calabrian Arc, and the Aegean Arc. The movement and forces at this plate boundary, especially during the late Miocene period, are closely linked to the Messinian salinity crisis. Tectonic activity may have opened or closed pathways between the Mediterranean and the Atlantic, as the region is filled with faults where rocks slide past each other and blocks of land rotate. As these faults adjusted to pressure from the African plate pushing toward Europe, the geography of the area may have changed enough to block or allow water flow. However, the exact tectonic processes behind these changes are still unclear.
Any explanation of these events must account for several features in the region. Three main geodynamic models have been proposed to explain the data. Of these, only the first model, which involves a process called rollback, seems to explain the observed rotations of land. However, this model is difficult to match with the temperature and pressure history of certain rocks. This has led scientists to combine ideas from different models in ways that initially seemed unusual.
Climate changes were likely important in causing the repeated events. These changes occurred during cool periods in the Milankovitch cycles, when less sunlight reached the northern hemisphere. This reduced evaporation in the North Atlantic, leading to less rainfall over the Mediterranean. With less water from rivers flowing into the sea, the basin may have dried up.
Large drops in sea level, caused by ice age conditions, likely influenced the connection between the Mediterranean and the Atlantic. A major drop of about 30 meters (98 feet) occurred around 5.26 million years ago, near the boundary between the Miocene and Pliocene periods. Earlier, around 6.14 million years ago, sea levels fell by about 10 meters (33 feet). These changes may have affected how water flowed between the two bodies of water.
Relationship to climate
The climate of the abyssal plain during the drought is not known. No place on Earth is similar to the dry Mediterranean, so scientists cannot study it by comparing it to other areas. Computer models that predict weather patterns can show possible effects of the drying, but there is no agreement on whether the Mediterranean Sea completely dried out. It is likely that three or four large salt lakes remained on the abyssal plains. Judging how much the area dried is difficult because salt layers reflect seismic waves, and drilling to study them is very hard.
Scientists can use information about wind to guess the climate. If winds moved across the "Mediterranean Sink," they would change temperature as they rose or fell. In a dry Mediterranean Basin, summer temperatures might have been extremely high. Using a simple rule that air warms about 10 degrees Celsius (18 degrees Fahrenheit) for every kilometer it rises, the hottest temperature at a spot 4 kilometers (2.5 miles) below sea level could be about 40 degrees Celsius (72 degrees Fahrenheit) warmer than at sea level. This would make temperatures near 80 degrees Celsius (176 degrees Fahrenheit) at the lowest points, which would not support most life but could allow special organisms called extremophiles. Air pressure would also increase at depths 3–5 kilometers (2–3 miles) below sea level, adding to the heat. However, these estimates are probably too extreme. A 2009 computer model showed that if the Mediterranean completely dried, summer temperatures would rise by up to 15 degrees Celsius (27 degrees Fahrenheit), and winter temperatures by 4 degrees Celsius (7.2 degrees Fahrenheit). If the sea level dropped slightly, temperatures would rise less. The model also showed changes in weather patterns across the Northern Hemisphere.
Today, water from the Mediterranean Sea provides rain that affects areas like Italy, Greece, and the Levant. Without this moisture, the climate in these regions would be drier, limited to places like the Iberian Peninsula and parts of North Africa. Areas in the central and eastern Mediterranean and nearby regions would be drier even above modern sea level. The eastern Alps, the Balkans, and the Hungarian plain would also be drier than they are today, even with the same wind patterns. However, the Paratethys ocean provided water to areas north of the Mediterranean. During the Miocene, the Wallachian-Pontic and Hungarian basins were underwater, changing the climate of the Balkans and other northern regions. The Pannonian Sea supplied water until the middle Pleistocene, after which it became the Hungarian plain. Scientists debate whether water from the Wallachian-Pontic basin (and possibly the Pannonian Sea) reached the eastern Mediterranean during the Miocene.
Effects
The Messinian salinity crisis caused many marine fish and other sea creatures in the basin to die out. After the crisis, the Mediterranean's current pattern of species variety, which decreases from west to east, began to form. Land mammals in the Mediterranean also lost many species. When the Iberian Peninsula and North Africa joined together, animals from these regions exchanged places. The crisis also allowed land animals to reach distant areas like the Balearic Islands. There, species such as the goat-antelope Myotragus remained separated until the Holocene, more than 5 million years later.
The idea that the Mediterranean Sea was completely dry during the Messinian has some related ideas.
Some believe that during the Messinian, the Red Sea was connected to the Mediterranean through the Suez area but was not linked to the Indian Ocean. The Red Sea may have dried up along with the Mediterranean.
Replenishment
When the Strait of Gibraltar was finally broken through, a huge amount of water from the Atlantic Ocean would have flowed through what was likely a narrow passage. This event was once thought to create a massive waterfall taller than today's Angel Falls, which is 979 meters (3,212 feet) high, and much stronger than both Iguazu Falls and Niagara Falls. However, recent research on underground formations near the Gibraltar Strait shows that the floodwater flowed into the dry Mediterranean Sea in a slow, gradual way.
A large layer of mixed rocks and sediment, carried by a powerful flood, has been discovered on the seabed southeast of Sicily's southern tip. Scientists believe this material was left behind by the Zanclean flood.