The
Messinian Salinity Crisis, also referred to as the
Messinian Event, is a period when the
Mediterranean SeaThe Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by Africa, and on the east by the Levant. The sea is technically a part of the Atlantic Ocean, although it...
evaporated partly or completely during the
MessinianThe Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.332 ± 0.005 Ma...
period of the
MioceneThe Miocene is a geological epoch of the Neogene period and extends from about 23.03 to 5.33 million years before the present . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the...
epoch, 5.96 million years ago.
Naming
Charles Mayer-Eymar (1826-1907) of Zurich studied fossils between
gypsumGypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO
4·2H
2O.-Crystal varieties:...
-bearing,
brackishBrackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salten" or "salty"...
and freshwater sediment layers and identified them as having been deposited just before the end of the
MioceneThe Miocene is a geological epoch of the Neogene period and extends from about 23.03 to 5.33 million years before the present . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the...
Epoch. In 1867 he named the period the Messinian, for the region of Messina,
SicilySicily is the largest island in the Mediterranean Sea. It is an autonomous region of Italy. Several much smaller islands surrounding it are considered to be part of Sicily....
. Since then salt-bearing and gypsum-bearing
evaporiteEvaporites are water-soluble mineral sediments that result from the evaporation of bodies of surficial water. Evaporites are considered sedimentary rocks.- Formation of evaporite rocks :...
layers in many Mediterranean countries have been dated to that period.
Discovery
In 1961, seismic surveying of the Mediterranean basin revealed a geological feature some 100-200 metres below the seafloor. This feature, dubbed the
M reflector, closely followed the contours of the present seafloor, suggesting that it was laid down evenly and consistently at some point in the past. Drilling experiments, conducted a decade later from the
Glomar ChallengerThe 120m long Glomar Challenger was a deep sea research and scientific drilling vessel for oceanography and marine geology studies. It was designed by the American National Science Foundation and University of California and built by Levingston Shipbuilding Company in Orange, Texas. Launched on...
under the supervision of co-chief scientists William B.F. Ryan and
Kenneth J. HsuKenneth J. Hsu Ph.D, M.A., born 28 June, 1929，is a Swiss scientist, geologist, paleoclimatologist, oceanographer, government advisor, author, inventor, entrepeneur, and polymath who was born in Nanjing, China.-Education:...
during Leg 13 of the
Deep Sea Drilling ProgramThe Deep Sea Drilling Project was anocean drilling project running from 1968 to 1983. The program is successful as evidenced by the data and publications that have resulted from it and is supported by Texas A&M.- See also :*Project Mohole...
, revealed the nature of the M reflector, a layer of
evaporiteEvaporites are water-soluble mineral sediments that result from the evaporation of bodies of surficial water. Evaporites are considered sedimentary rocks.- Formation of evaporite rocks :...
s up to 3 kilometres thick.
Evidence
Sediment samples from below the deep seafloor of the Mediterranean Sea, which include
evaporiteEvaporites are water-soluble mineral sediments that result from the evaporation of bodies of surficial water. Evaporites are considered sedimentary rocks.- Formation of evaporite rocks :...
minerals, soils, and
fossilFossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and sedimentary layers is known as the fossil record...
plants, show that about 5.9 million years ago in the late
MioceneThe Miocene is a geological epoch of the Neogene period and extends from about 23.03 to 5.33 million years before the present . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the...
period the precursor of the modern
Strait of GibraltarThe Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain from Morocco...
closed tight, and the Mediterranean Sea evaporated into a deep dry basin with a bottom at some places 2 to 3 miles (3.2 to 4.9 km) below the world ocean level. Even now the Mediterranean is saltier than the North Atlantic because of its near isolation by the Straits of Gibraltar and its high rate of
evaporationEvaporation is the vaporization of a liquid and the reverse, of condensation. A type of phase transition, it is the process by which molecules in a liquid state spontaneously become gaseous . Generally, evaporation can be seen by the gradual disappearance of a liquid from a substance when exposed...
.
If the Strait of Gibraltar closes again, which is likely to happen in the near geological future (though extremely distant on a human time scale), the Mediterranean would mostly evaporate in about a thousand years.
The first solid evidence for the ancient
desiccationDesiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately-well sealed container.-Science:-Desiccator:...
of the Mediterranean Sea came in the summer of 1970, when geologists aboard the
Deep Sea Drilling ProgramThe Deep Sea Drilling Project was anocean drilling project running from 1968 to 1983. The program is successful as evidenced by the data and publications that have resulted from it and is supported by Texas A&M.- See also :*Project Mohole...
drillship
Glomar ChallengerThe 120m long Glomar Challenger was a deep sea research and scientific drilling vessel for oceanography and marine geology studies. It was designed by the American National Science Foundation and University of California and built by Levingston Shipbuilding Company in Orange, Texas. Launched on...
brought up drill cores containing
arroyoAn arroyo , also called a wash or draw, is a usually dry creek bed or gulch that temporarily fills with water after a heavy rain, or seasonally. As such, the term is similar to the word wadi. Arroyos can be natural or man-made. The term usually applies to a mountainous desert environment...
gravels and red and green
floodplain||-||-||-||-||-||-||-||}A floodplain, or flood plain, is flat or nearly flat land adjacent to a stream or river that experiences occasional or periodic flooding...
silts; and
gypsumGypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO
4·2H
2O.-Crystal varieties:...
,
anhydriteAnhydrite is a mineral - anhydrous calcium sulfate, CaSO
4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from...
,
rock saltHalite is the mineral form of sodium chloride, NaCl, commonly known as rock salt. Halite forms isometric crystals. The mineral is typically colorless to yellow, but may also be light blue, dark blue, and pink depending on the amount and type of impurities...
, and various other
evaporiteEvaporites are water-soluble mineral sediments that result from the evaporation of bodies of surficial water. Evaporites are considered sedimentary rocks.- Formation of evaporite rocks :...
minerals that often form from drying of
brineBrine is water saturated or nearly saturated with a salt .It is used to preserve vegetables, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses.Brine is a common fluid used in large refrigeration installations for the transport of heat from...
or seawater, including in a few places
potashPotash is the common name given to potassium carbonate and various mined and manufactured salts that contain the element potassium in water-soluble form. In some rare cases, potash can be formed with traces of organic materials such as plant remains....
, left where the last bitter, mineral-rich waters dried up. One drill core contained a wind-blown cross-bedded deposit of deep-sea
foraminiferaThe Foraminifera, or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net. They typically produce a test, or shell, which can have either one or multiple chambers, some becoming quite elaborate...
l ooze that had dried into dust and been blown about on the hot dry
abyssal plainAbyssal plains are flat or very gently sloping areas of the deep ocean basin floor. They are among the Earth's flattest and smoothest regions and the least explored. Abyssal plains cover approximately 40% of the ocean floor and reach depths between...
by
sandstormSandstorm can refer to:* Dust storm, a storm caused by strong winds and blowing sand or dust* "Sandstorm ", an electronica song by Darude* "Sandstorm", a song by Level 42 on the album Strategy* Sandstorm: The Jim Boz Dance Company...
s and ended up in a
brineBrine is water saturated or nearly saturated with a salt .It is used to preserve vegetables, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses.Brine is a common fluid used in large refrigeration installations for the transport of heat from...
lake interbedded between two layers of
haliteHalite is the mineral form of sodium chloride, NaCl, commonly known as rock salt. Halite forms isometric crystals. The mineral is typically colorless to yellow, but may also be light blue, dark blue, and pink depending on the amount and type of impurities...
. These layers alternated with layers containing marine fossils, indicating a succession of drying and flooding periods. Other evidence of drying comes from the remains of many (now submerged) canyons that were cut into the sides of the dry Mediterranean basin by rivers flowing down to the
abyssal plainAbyssal plains are flat or very gently sloping areas of the deep ocean basin floor. They are among the Earth's flattest and smoothest regions and the least explored. Abyssal plains cover approximately 40% of the ocean floor and reach depths between...
. For example, the
NileThe Nile is a major north-flowing river in Africa, generally regarded as the longest river in the world....
cut its bed down to several hundred feet below sea level at
AswanAswan, formerly spelled Assuan, is a city in the south of Egypt, the capital of the Aswan Governorate....
(where Ivan S. Chumakov found marine Pliocene foraminifers in 1967), and 8,000 feet (2,400
mThe metre or meter is the basic unit of length in the International System of Units . Historically, the metre was defined by the French Academy of Sciences as the length between two marks on a platinum-iridium bar, which was designed to represent one ten-millionth of the distance from the Equator...
) below sea level under
CairoCairo is the capital of Egypt and the largest city in the Arab World. Nicknamed "The City of a Thousand Minarets" for its preponderance of Islamic architecture, Cairo has long been a center of the region's political and cultural life...
. Fossilized cracks were found where muddy sediment had dried and cracked in the sunlight and drought. The area was repeatedly flooded and desiccated over the course of 700,000 years. About 5.4 million years ago, at the start of the
PlioceneThe Pliocene epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present....
period the barrier at the Strait of Gibraltar broke, permanently reflooding the basin.
Some of these Messinian deposits have since been pushed up onto land by later tectonic activity in Messina (Sicily), northeast Libya, Italy, and southern Spain.
Chronology
Based on palaeomagnetic datings of
MessinianThe Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.332 ± 0.005 Ma...
deposits that have since been brought above sea level by tectonic activity, the salinity crisis started at the same time over all the Mediterranean basin, at 5.96 ± 0.02 million years ago. The basin was isolated from the
Atlantic OceanThe Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about 106.4 million square kilometres , it covers approximately one-fifth of the Earth's surface and about one-quarter of its water surface area. The first part of its name refers to the Atlas of Greek...
between 5.59 and 5.33 million years ago, resulting in a huge decrease in the Mediterranean sea level. During the initial stages (5.59 - 5.50 million years ago) there was extreme erosion, creating several huge canyon systems (some similar in scale to the
Grand CanyonThe Grand Canyon is a steep-sided gorge carved by the Colorado River in the United States in the state of Arizona. It is largely contained within the Grand Canyon National Park, one of the first national parks in the United States...
) around the Mediterranean. Later stages (5.50 - 5.33 million years ago) are marked by cyclic
evaporiteEvaporites are water-soluble mineral sediments that result from the evaporation of bodies of surficial water. Evaporites are considered sedimentary rocks.- Formation of evaporite rocks :...
deposition into a large "lake-sea" basin.
Several cycles
The enormous volume of extant Messinian evaporites could not have been deposited during a single event. Furthermore, the nature of the
strataIn geology and related fields, a stratum is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. Each layer is generally one of a number of parallel layers that lie one upon another, laid down by natural forces. They may extend over...
points strongly to several cycles of the Mediterranean Sea completely drying up and being refilled, with "drying up" periods correlating to periods of cooler global temperature - which were therefore drier in the Mediterranean region. Each refilling was presumably caused by a seawater inlet opening either tectonically or by a river flowing eastwards below sea level into the "Mediterranean Sink" cutting its valley head back west until it let the sea in, similarly to a
river captureStream capture, river capture, or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighbouring stream...
. The last refilling was at the
MioceneThe Miocene is a geological epoch of the Neogene period and extends from about 23.03 to 5.33 million years before the present . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the...
/
PlioceneThe Pliocene epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present....
boundary, when the
Strait of GibraltarThe Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain from Morocco...
broke wide open permanently. Upon closely examining the Hole 124 core,
Kenneth J. HsuKenneth J. Hsu Ph.D, M.A., born 28 June, 1929，is a Swiss scientist, geologist, paleoclimatologist, oceanographer, government advisor, author, inventor, entrepeneur, and polymath who was born in Nanjing, China.-Education:...
found that:
Dehydrated geography
The notion of a completely waterless Mediterranean Sea has some corollaries.
- At the time, the Strait of Gibraltar
The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain from Morocco...
was not open, but other seaways (the Betic corridor to the north where the Sierra NevadaThe Sierra Nevada, meaning "snowy range" in Spanish, is a mountain range in the region of Andalusia in Spain. It contains the highest point of continental Spain, Mulhacén at ....
or Baetic CordilleraThe Baetic Cordillera is a mountain system in the southern and eastern Spain. Also known as the Baetic ranges or Baetic mountains, and in Spanish as the Sistema Penibético, the Baetic Cordillera is made up of multiple mountain ranges that reach from western Andalusia to Murcia and Valencia,...
is now), the Rifean corridor or corridors where the Rif Mountains are now) to the south) linked the Mediterranean to the Atlantic. These must have closed to isolate the basin from the open ocean.
- The high level of salinity cannot be tolerated by many known organisms, most likely reducing the biodiversity of much of the basin.
- The basin's low altitude would have made it extremely hot during the summer through adiabatic heating
In thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which no heat is transferred to or from the working fluid. The term "adiabatic" literally means impassable, coming from the Greek roots ἀ- , διὰ- , and βαῖνειν ; this etymology corresponds here to an...
, evidence supported by the presence of anhydriteAnhydrite is a mineral - anhydrous calcium sulfate, CaSO
4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from...
, which is only deposited in water warmer than 35°C (95°F).
- Rivers emptying into the basin would have cut their beds much deeper (at least a further 2,400 m or 8,000 feet in the case of the Nile
The Nile is a major north-flowing river in Africa, generally regarded as the longest river in the world....
, as the buried canyon under CairoCairo is the capital of Egypt and the largest city in the Arab World. Nicknamed "The City of a Thousand Minarets" for its preponderance of Islamic architecture, Cairo has long been a center of the region's political and cultural life...
shows).
Climate
The climate of the abyssal plain during the drought is unknown. There is no situation on Earth directly comparable to the dry Mediterranean, and thus it is not possible to know its climate. There is not even a consensus as to whether the Mediterranean Sea even dried out completely; it seems likeliest that at least three or four large
brine lakeBrine lakes consist of water that has reached salt saturation or near saturation , and may also be heavily saturated with other materials....
s on the
abyssal plainAbyssal plains are flat or very gently sloping areas of the deep ocean basin floor. They are among the Earth's flattest and smoothest regions and the least explored. Abyssal plains cover approximately 40% of the ocean floor and reach depths between...
s remained at all times. The extent of desiccation is very hard to judge due to the reflective seismic nature of the salt beds, and the difficulty in drilling cores, making it difficult to map their thickness.
Nonetheless, one can study the forces at play in the atmosphere to arrive at a good speculation of the climate. As winds blew across the "Mediterranean
SinkIn geography a sink is an area of dry land below sea-level, for example the Salton Sink and the Afar Depression.Sinks tend to occur in arid areas where evaporation exceeds rainfall and the sea cannot enter.-In the past:...
", they would heat or cool adiabatically with altitude. As a result, the rule that "cold air falls and hot air rises" has to be adjusted by considering how hot each bit of air would be if brought adiabatically to sea-level pressure.
In the empty Mediterranean Basin the summertime temperatures would likely have been extremely high. Using the
Clausius-Clapeyron relationThe Clausius–Clapeyron relation, named after Rudolf Clausius and Émile Clapeyron, who defined it sometime after 1834, is a way of characterizing a discontinuous phase transition between two phases of matter. On a pressure–temperature diagram, the line separating the two phases is known as the...
, one can derive an equation showing that a theoretical temperature of an area 4 kilometers (= 2.485 miles) below sea level would be about 40°C (104°F) warmer than the temperature at sea level. Thus one could predict theoretical temperature maximums of around 80°C (176 °F) at the lowest depths of the dry abyssal plain permitting little known life to survive there. One can also calculate that 2 to 3 miles below sea level would have resulted in 1.45 to 1.71 atm (1,102 to 1,300 mmHg) of air pressure at the bottom. Although it was likely quite dry in the Basin, there is no direct way to measure how much drier it would have been compared to its surroundings. Areas with less severe depths would likely have been very dry.
Today the evaporation from the Mediterranean Sea supplies moisture that falls in frontal storms, but without such moisture, the
Mediterranean climateA hi Mediterranean climate resembles the climate of the lands in the Mediterranean Basin, which includes most of the area with this climate type worldwide...
that we associate with Italy, Greece, and the Levant would be limited to the
Iberian PeninsulaThe Iberian Peninsula, or Iberia, is located in the extreme southwest of Europe and includes modern-day Spain, Portugal, Andorra and Gibraltar and a very small area of France. It is the westernmost of the three major southern European peninsulas—the Iberian, Italian, and Balkan peninsulas...
and the western
MaghrebThe Maghreb , also rendered Maghrib , meaning "place of sunset" or "western" in Arabic, is a region in North Africa. The term is generally applied to all of Morocco, Algeria, and Tunisia, but in older Arabic usage pertained only to the area of the three countries between the high ranges of the...
. Climates throughout the central and eastern basin of the Mediterranean and surrounding regions to the north and east would have been drier even above modern sea level. The eastern Alps, the Balkans, and the Hungarian plain would also be much drier than they are today, even if the westerlies prevailed as they do now. However, the
ParatethysThe Paratethys ocean, Paratethys sea or just Paratethys was a large shallow sea that stretched from the region north of the Alps over Central Europe to the Aral sea in western Asia...
ocean provided water to the area north of the Mediterranean basin. The Wallachian-Pontic and Hungarian basins were underwater during the Miocene, modifying the climate of what is now the Balkans and other areas north of the Mediterranean basin. The
Pannonian SeaThe Pannonian Sea was a shallow ancient sea located in the area today known as the Pannonian Plain in Central Europe. The Pannonian Sea existed during the Miocene and Pliocene epochs, when three to four kilometres of marine sediments were deposited in the Pannonian Basin.-History:The Pannonian Sea...
was a source of water north of the Mediterranean basin until the middle Pleistocene before becoming the Hungarian plain. Debate exists whether the waters of the Wallachian-Pontic basin (and the possibly connected
Pannonian SeaThe Pannonian Sea was a shallow ancient sea located in the area today known as the Pannonian Plain in Central Europe. The Pannonian Sea existed during the Miocene and Pliocene epochs, when three to four kilometres of marine sediments were deposited in the Pannonian Basin.-History:The Pannonian Sea...
) would have had access (thus bringing water) to at least the eastern Mediterranean basin at times during the Miocene.
Multiple basins
As the level of the Mediterranean fell, smaller basins on its flanks became isolated from the main sea. The timing and mode of the desiccation of these smaller basins, such as the Tabernas basin and
Sorbas basinThe Sorbas basin is a sedimentary basin around the town of Sorbas in south-east Spain. It is believed to have been formed by extension, between two fault-bounded blocks which rotated anti-clockwise to take up the compression resulting from Europe's collision with Africa...
, is still debated.
One school of thought holds that there was still limited connection to the open ocean, so basins further from the seaway dried out first, with shallow lakes between the deepest parts of the Mediterranean and the gateway. In other words, deposition was diachronous, as in image a.
Another school suggests that desiccation was synchronous, but occurred mainly in shallower basins. This model would suggest that the sea level of the whole Mediterranean basin fell at once, but only shallower basins dried out enough to deposit salt beds. See image b.
The final suggestion is that desiccation was synchronous and basin wide, with sea level potentially falling to rock bottom. Salts would be deposited in all Mediterranean basins, as in image c.
Distinguishing between these hypotheses requires the calibration of gypsum deposits. Gypsum is the first salt to be deposited from a desiccating basin.
MagnetostratigraphyMagnetostratigraphy is a chronostratigraphic technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their detrital remanent magnetization , that is, the polarity...
offers a broad constraint on timing, but no fine detail. Therefore,
cyclostratigraphyCyclostratigraphy is the study of astronomically forced climate cycles within sedimentary successions. Astronomical cycles are variations of the Earth's orbit around the sun due to the gravitational interaction with other masses within the solar system. Due to this cyclicity solar irradiation...
is relied upon to compare the dates of sediments.
The typical case study compares the gypsum evaporites in the main Mediterranean basin with those of the
Sorbas basinThe Sorbas basin is a sedimentary basin around the town of Sorbas in south-east Spain. It is believed to have been formed by extension, between two fault-bounded blocks which rotated anti-clockwise to take up the compression resulting from Europe's collision with Africa...
, a smaller basin on the flanks of the Mediterranean Sea that is now exposed in southern Spain. The relationship between these two basins is assumed to represent the relationships of the wider region.
Recent work has relied on cyclostratigraphy to correlate the underlying marl beds, which appear to be have given way to gypsum at exactly the same time in both basins. The proponents of this hypothesis claim that cyclic variations in bed compositions are astronomically tuned, and the beds' magnitude can be calibrated to show they were contemporaneous - a strong argument. In order to refute it, it is necessary to propose an alternative mechanism for generating these cyclic bands, or for erosion to have coincidentally removed just the right amount of sediment everywhere before the gypsum was deposited. The proponents claim that the gypsum was deposited directly above the correlated marl layers, and slumped into them, giving the appearance of an unconformable contact. However, their opponents seize upon this apparent unconformity, and claim that the Sorbas basin was exposed - therefore eroding - while the Mediterranean sea was depositing evaporites. This would result in the Sorbas basin being filled with evaporites at 5.5 million years ago (Ma), compared to the main basin at 5.96 Ma.
Global effects
The water from the Mediterranean would have been redistributed in the world ocean, raising global sea level by as much as 10 meters (~33 feet).
http://www.geo.arizona.edu/geo2xx/geo212.034/Lect17.html The Mediterranean basin also sequestered below its seabed a significant percentage of the salt from Earth's oceans; this decreased the average salinity of the world ocean and raised its freezing point.
Causes
Several possible causes of the series of Messinian crises have been considered. While there is disagreement on all fronts, the most general consensus seems to agree that climate had a role in forcing the periodic filling and emptying of the basins, and that tectonic factors must have played a part in controlling the height of the sills restricting flow between the Atlantic and Mediterranean. The magnitude and extent of these effects, however, is widely open to interpretation.
Tectonic reconfiguration may have closed and re-opened passages; the region is permeated by strike-slip faults and rotating blocks of continental crust. As faulting accommodated the regional compression caused by Africa's convergence with Eurasia, the geography of the region may have altered enough to open and close seaways. However, the precise tectonic activity behind the motion can be interpreted in a number of ways.
Any model must explain a variety of features of the area:
- Shortening and extension occur at the same time in close proximity; sediments constrain the rates of uplift and subsidence quite precisely
- Fault-bounded continental blocks can be observed to rotate
- The depth and structure of the lithosphere
The lithosphere is the rigid outermost shell of a rocky planet.- Earth's lithosphere :...
is constrained by records of seismic activity, as well as tomographyTomography is imaging by sections or sectioning, through the use of wave of energy. A device used in tomography is called a tomograph, while the image produced is a tomogram. The method is used in medicine, archaeology, biology, geophysics, oceanography, materials science, astrophysics and other...
- The composition of igneous rocks varies - this constrains the location and extent of any subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. A subduction zone is an area on Earth where two tectonic plates move towards one another and...
.
There are three contending models that may fit the data.
- A moving subduction zone may have caused regional uplift. Changes in volcanic rocks suggest that subduction zones at the rim of the Tethys Sea may have rolled back westwards, changing the chemistry and density in magma underlying the western Mediterranean. However, this does not account for the periodic emptying and refilling of the basin.
- The same features can be explained by regional delamination
Delamination is a mode of failure for composite materials. Mode of failure are also known as 'failure mechanism'. In laminated materials repeated cyclic stresses, impact, and so on can cause layers to separate, forming a mica-like structure of separate layers, with significant loss of mechanical...
, the loss of a layer of the entire lithosphere.
- Deblobbing, the loss of a "blob" of lithospheric mantle, and the subsequent upward motion of the overlying crust (which has lost its dense mantle "anchor") may also have caused the observed phenomena, although the validity of the "deblobbing" hypothesis has been called into question.
Of these, only rollback can explain the rotations observed. However, it is difficult to fit it with the pressure and temperature histories of some metamorphic rocks. This has led to some bizarre and interesting combinations of the models, in attempts to approach the true state of affairs.
Changes in climate must almost certainly be invoked to explain the periodic nature of the events. They occur during cool periods of Milankovic cycles, when less solar energy reached the Earth. This led to less evaporation of the North Atlantic, hence less rainfall over the Mediterranean. This would have starved the basin of water supply from rivers and allowed its desiccation.
Contrary to many people's instincts, global sea level fluctuations cannot have played a role. The lack of ice caps at the time means there was no realistic mechanism to cause significant changes in sea level - there was nowhere for the water to go, and the morphology of ocean basins cannot change on such a short timescale.
Replenishment
When the
Strait of GibraltarThe Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain from Morocco...
was ultimately breached, the
Atlantic OceanThe Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about 106.4 million square kilometres , it covers approximately one-fifth of the Earth's surface and about one-quarter of its water surface area. The first part of its name refers to the Atlas of Greek...
would have poured a vast volume of water through what would have presumably been a relatively narrow channel. The resulting
waterfallA waterfall is a place where flowing water rapidly drops in elevation as it flows over a steep region or a cliff.-Formation :Typically, a river flows over a large step in the rocks that may have been formed by a fault line. As it increases its velocity at the edge of the waterfall, it plucks...
could have been higher than
Angel FallsAngel Falls is the world's highest waterfall, with a height of 979 m and a clear drop of 807 m...
is today (979 m), and far more powerful than either
Iguazu FallsIguazu Falls, Iguassu Falls, or Iguaçu Falls Iguazu Falls, Iguassu Falls, or Iguaçu Falls Iguazu Falls, Iguassu Falls, or Iguaçu Falls ' onMouseout='HidePop("8784")' href="http://www.absoluteastronomy.com/topics/Niagara_Falls">Niagara Falls
The Niagara Falls are voluminous waterfalls on the Niagara River, straddling the international border between the Canadian province of Ontario and the U.S. state of New York...
, or
Victoria FallsThe Victoria Falls or Mosi-oa-Tunya is a waterfall located in southern Africa on the Zambezi River between the countries of Zambia and Zimbabwe. The falls are some of the largest in the world.-Introduction:...
.
In popular culture
Even before 1961, there had been speculations about a possible dehydration of the Mediterranean Sea in the distant past.
- In the first century, Pliny the Elder
Gaius Plinius Secundus , better known as Pliny the Elder, was an author, naturalist, and natural philosopher as well as naval and army commander of the early Roman Empire and personal friend of the emperor Vespasian...
recounted a popular story in his Natural History according to which the Mediterranean Sea was created when the Atlantic ocean gained admission through the Strait of Gibraltar:
- In 1920, H. G. Wells
Herbert George Wells was an English author, best known for his work in the science fiction genre. He was also a prolific writer in many genres, including contemporary novels, history, and social commentary....
published a popular history book in which it was suspected that the Mediterranean basin had in the past been cut off from the Atlantic. One piece of physical evidence, a deep channel past Gibraltar, had been noticed. Wells estimated that the basin had refilled roughly between 30,000 and 10,000 B.C. The theory he printed was that:
- In the last Ice Age
The general term "ice age" or, more precisely, "glacial age" denotes a geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in an expansion of continental ice sheets, polar ice sheets and alpine glaciers. Within a long-term ice age, individual...
, so much ocean water was taken into the icecaps that world ocean level dropped below the sill in the Strait of GibraltarThe Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain from Morocco...
.
- Without the inflow from the Atlantic the Mediterranean would evaporate much more water than it receives, and would evaporate down to two large lakes, one on the Balearic Abyssal Plain, the other further east.
- The east lake would receive most of the incoming river water, and may have overflowed into the west lake.
- All or some of this seabed may have had a human population, where it was watered from the incoming rivers.
- There is a long deep submerged valley running from the Mediterranean out into the Atlantic.
- But the Strait of Gibraltar
The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain from Morocco...
is 320 m deep, and global sea levels during the most recent Ice AgeThe general term "ice age" or, more precisely, "glacial age" denotes a geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in an expansion of continental ice sheets, polar ice sheets and alpine glaciers. Within a long-term ice age, individual...
are believed to have lowered sea levels by only about 100 m, so the basin was not dry during the Ice Age. That there had been an extreme drying event in the region earlier, was to be discovered forty years later.
- Robert E. Howard
Robert Ervin Howard was an American author who wrote pulp fiction in a diverse range of genres. His most famous character — created in the pages of the Depression-era pulp magazine Weird Tales — is Conan the Barbarian.With Conan and his other heroes, Howard created the genre of...
's Conan the BarbarianConan the Barbarian is a fictional character in books, comics and movies. He is a hero, a well known and iconic figure in American fantasy, and the most famous barbarian in fiction.Conan is often associated with the fantasy subgenre of sword-and-sorcery and heroic fantasy...
stories (1932) picture a Hyborian AgeThe Hyborian Age is a phrase used by author Robert E. Howard to refer to a specific epoch in a fictional timeline used for many of the low fantasy tales of his artificial legendry; in particular, the stories of Conan the Barbarian....
where the Mediterranean Sea and Black Sea are both dry.
- Poul Anderson
Poul William Anderson was an American science fiction author who wrote during a Golden Age of the genre. Anderson also authored several works of fantasy....
's Time Patrol story "Gibraltar Falls" (1975) takes place while the Atlantic begins to fill the Mediterranean Sea; here "falls" means "waterfallA waterfall is a place where flowing water rapidly drops in elevation as it flows over a steep region or a cliff.-Formation :Typically, a river flows over a large step in the rocks that may have been formed by a fault line. As it increases its velocity at the edge of the waterfall, it plucks...
".
- Harry Turtledove
Harry Norman Turtledove is an American novelist, who has produced works in several genres including alternate history, historical fiction, fantasy and science fiction.- Life :...
's novella "Down in the BottomlandsDown in the Bottomlands is a novella written by Harry Turtledove which takes places in an alternative history in which the Atlantic Ocean did not reflood the Mediterranean Sea 5.5 million years ago in the Miocene Epoch, as it did in our history...
," which takes place on an alternate Earth where the Mediterranean Sea stayed empty, and void of water, and part of it is a national parkA national park is a reserve of natural or semi-natural land, declared or owned by a national government, set aside for human recreation and enjoyment, and protected from most development...
to the countries around it, none of which are nations that we are familiar with in the real world. In this continuum, other differences that might have developed are:
- Egypt
Egypt , officially the Arab Republic of Egypt, is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Western Asia...
as we know it would not have developed: little or no agriculture would be possible in the Nile's canyon, and the Nile's alluvial fanAn alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain...
in the "Mediterranean Sink" would be too hot for human habitation. The Nile canyon would have been a major barrier to travel.
- Harsher climates and extensive zones of impassable desert between habitable areas rendered the economic and material basis of classical civilization
A civilization is a complex society or culture group characterized by dependence upon agriculture, long-distance trade, state form of government, occupational specialization, population, and class stratification.-Definition:...
s so different that any ancient civilizations in PhoeniciaPhoenicia what is now modern day Lebanon, was an ancient civilization centered in the north of ancient Canaan, with its heartland along the coastal regions of modern day Lebanon, extending to parts of Israel, Syria and Palestine...
, GreeceAncient Greece is the civilisation belonging to the period of Greek history lasting from the Greek Dark Ages ca. 1100 BC and the Dorian invasion, to 146 BC and the Roman conquest of Greece after the Battle of Corinth. It is generally considered to be the seminal culture which provided the...
, RomeThe Roman Republic was the phase of the ancient Roman civilization characterized by a republican form of government. It began with the overthrow of the Roman monarchy, c...
, and CarthageCarthage refers both to an ancient city in present-day Tunisia, and a modern-day suburb of Tunis. The civilization that developed within the city's sphere of influence is referred to as Punic or Carthaginian...
would have been very different or impossible.
- An early Dan Dare
Dan Dare is a British science fiction comic hero, created by illustrator Frank Hampson. Hampson not only invented Dan Dare and his entire world, he also put together the original team of artists and wrote the first two stories...
science fictionScience fiction is a genre of fiction. It differs from fantasy in that, within the context of the story, its imaginary elements are largely possible within scientifically-established or scientifically-postulated laws of nature...
comic story says as a side remark that (in its time line) the Mediterranean stayed dry until Neolithic times and was flooded by alien spaceships exploding, breaking the Strait of Gibraltar open.
- A draft version of the Space Odyssey series says that (in its time line) the Mediterranean bed stayed dry into human times and that the legend of Atlantis
Atlantis is a legendary island first mentioned in Plato's dialogues Timaeus and Critias.In Plato's account, Atlantis was a naval power lying "in front of the Pillars of Hercules" that conquered many parts of Western Europe and Africa 9,000 years before the time of Solon, or approximately 9600 BC...
derived from the Mediterranean reflooding.
- The episode "The Vanished Sea" of the Animal Planet
Animal Planet is an American satellite and cable television channel , that launched on October 1, 1996. It is distributed by Discovery Communications...
/ORFORF is the Austrian national public service broadcaster. Funded from a combination of a television licence fees and revenue from limited on-air advertising, ORF is the dominant player in the Austrian broadcast media...
/ZDFZweites Deutsches Fernsehen , ZDF, is a public-service German television channel based in Mainz. It is run as an independent non-profit agency established by joint contract between the German federal states...
-produced television series The Future Is WildThe Future Is Wild was a Canadian 2003 joint Animal Planet/ORF and ZDF co-production, which used computer-generated imagery to show the possible future of life on Earth...
posits a world 5 million years in the future where the Mediterranean Basin has again dried up, and explores what kind of life could survive the new climate.
- Julian May
Julian May is an American science fiction writer, best known for her Saga of Pliocene Exile and Galactic Milieu books.-Biography:...
's 1980's science fiction books The Many Coloured LandThe Many-Coloured Land is the first book of the Saga of the Exiles by Julian May. It sets the series up by introducing the story of each of the characters...
and The Golden Torc are set in Europe just before and during the rupture at Gibraltar. The rupture and the rapid filling of the Mediterranean form a Wagnerian climax to the The Golden Torc, in which aliens and time-traveling humans are caught up in this cataclysm.
Sources
- Kenneth J. Hsu
Kenneth J. Hsu Ph.D, M.A., born 28 June, 1929，is a Swiss scientist, geologist, paleoclimatologist, oceanographer, government advisor, author, inventor, entrepeneur, and polymath who was born in Nanjing, China.-Education:...
, The Mediterranean Was a Desert: A Voyage of the Glomar Challenger, Princeton University Press, ISBN 0-691-02406-5
External links
- The Messinian Salinity Crisis by Ian West (Internet Archive copy)
- The Messinian Salinity Crisis by Rob Butler
- Messinian online