[ICTJA-CSIC's Press Note on our own research (see open access article linked at the foot of this page)]
A study conducted by an international team of scientists has found new evidence supporting the hypothesis of a mega-flood occurring during the Zanclean period, in which water from the Atlantic poured back into the Mediterranean sea and ended the Messinian Salinity Crisis (MSC) 5 million years ago. The study, led by Professor Aaron Micallef from the University of Malta, has been published in the Scientific Reports journal.
Recreation of the evolution of the Messinian salinity crisis, between 6 and 5.3 milion years ago. This is one of the scenarios competing among the scientific community studying this period. Time scale (milion years per second) not to scale. [Credit: Univ. of Malta]
Using seismic profiles and borehole data from offshore eastern Sicily, researchers have identified a large body of sediments buried in the subsurface of Sicily Channel which are characterized as being "extensive" and "chaotic." They have named this mass of material Unit 2.
The study says that this huge mass of sediments is composed of materials eroded and transported by the great flow of water that flooded the Ionian Basin through the Strait of Sicily once the western basin of the Mediterranean was refilled with the contribution of water coming from the Atlantic Ocean that had poured in previously through the Strait of Gibraltar. This event is known as Zanclean megaflood.
Location and geometry of the "Unit 2" corresponding to the sediment body originated by the Zanclean megaflood. Source: Aaron Micallef (University of Malta)
The discovered sediments have been located over a layer of salts originated previously during the partial desiccation of the Mediterranean Sea during the MSC and under another layer of common marine sediments that were deposited after the flood and during the restoration of the normal marine conditions.
"The deposits identified in our study have little reflectivity of the seismic waves, they are seismically transparent, and present a disordered internal structure of the layers which is very similar to the sediments typically originated in catastrophic floods," explains Daniel García-Castellanos, co-author of the study and researcher from Barcelona's Institute of Earth Sciences Jaume Almera of the CSIC (ICTJA-CSIC).
The study indicates that the sedimentary body found next to the base of the Malta Escarpment, between the eastern and western Mediterranean Sea, is wedge-shaped, and its estimated thickness is up to 860 meters in some parts. According to the researchers, it would be the largest known megaflood deposit on Earth.
"According to the models of the paper that we published in Nature in 2009, the flood would have lasted only a few years, reaching discharges of up to 100 million cubic meters per second, about a rate thousand times the current flow of the Amazon River," adds García-Castellanos.
Researchers have also identified a spot in the channel of Sicily as the most likely gateway for the eastern Mediterranean Zanclean flood across the Malta escarpment, the submarine canyon of Noto (southeast Sicily). The authors of the study explain that this canyon has a unique morphology—its amphitheatre-shaped head is 6 km wide and is "similar to that of bedrock canyons rapidly eroded by megafloods. "The researchers interpret the Noto submarine canyon as the collector of the cascading flow into the Ionian Basin.
The study points to the abrupt and catastrophic nature of the environmental changes that occurred during the Messinian period, the most important since the dinosaurs' extinction 65 million years ago," says Daniel García-Castellanos.
The Messinian Salinity Crisis: an unrecognizable Mediterranean Sea
About 6 million years ago, the connection between the Atlantic Ocean and the Mediterranean Sea was interrupted. This event led to the partial desiccation of the Mediterranean Sea, which became a giant saline lake, with an estimated sea-level drawdown of 1300-2400 meters. This event is known as Messinian Salinity Crisis (MSC).
A major open question about this period is how normal marine conditions were restored. The hypothesis of the Zanclean megaflood proposes that there was a massive inflow of water through the Strait of Gibraltar that first flooded the western Mediterranean Basin. Then, through the Strait of Sicily, which was once the division between the eastern and western basins, flooded the Ionian Basin. Some studies indicate that this filling process lasted between a few months and two years.
Micallef, A., et al. (2018), Evidence of the Zanclean megaflood in the eastern Mediterranean Basin, Scientific Reports, 8(1), 1078, DOI: 10.1038/s41598-018-19446-3
Artistic interpretation of the proposed lowstand
of the Mediterranean level during the salinity
crisis. Authors: Pibernat and Garcia-Castellanos
130 years have gone by since the scientific recognition of a hypersaline Mediterranean sea around 6 million years ago;
50 years have passed since documenting widespread submarine and riverine erosional features that suggest a subaerial exposure of parts of the Mediterranean Sea;
We are 40 years after the first abissal drilling reaching the top of a salt layer thicker than 1 kilometer...
And yet, the most intriguing and debated question around the Messinian salinity crisis remains whether there was a large sea level fall during the crisis, more than a few hundreds of meters, perhaps more than a kilometer. Evidence in favor and against is piling up on the desks of geoscientists.
We now publish a new piece of evidence that supports a Yes answer to this long-standing question. A fall in the level of the Mediterranean Sea about 6 million years ago may have increased volcanic activity over the entire region (Sternai et al., 2017, Nature Geosc.).
Geoscientists inspecting the Realmonte mine in Sicily,
where Messinian salt is commercialized.
A layer ranging from 1 to 2 km of salt (halite) spreads below much of the Mediterranean seabed, formed when the Mediterranean Sea became isolated from the Atlantic Ocean about 6.0 to 5.3 million years ago, leading to evaporation and sea-level fall in an event known as the Messinian salinity crisis. The rate and amount of sea-level fall in the Mediterranean during this time is strongly debated. However, if the sea-level drop was dramatic and rapid, it could have unloaded the Earth’s surface, decompressing the mantle below. Such mantle decompression can enhance magma production and, in turn, lead to more frequent volcanic eruptions at the surface.
Pietro Sternai and the rest of us test this idea using a combination of geological data and numerical modelling. Dated magma intrusions and volcanic eruptions in the region show that there was a pulse of increased volcanic activity towards the end of the Messinian salinity crisis. By calculating changes in the surface load caused by a kilometre-scale drop in sea level, and taking into account the counter weight of the increased density of the remaining highly saline water and accumulating salt deposits we verify that such changes in sea level are sufficient to unload and decompress the mantle, triggering a significant increase in volcanism over the Mediterranean.
Decompression and vertical rebound of the lithosphere
in response to a sudden evaporation of the sea.
The results provide independent support for the idea that sea-level fall during the Messinian salinity crisis was rapid and occurred on a dramatic scale, and also highlights the sensitivity of Earth’s solid interior to changes at the surface.
Check also the News & Views article by Jean-Arthur Olive: “This proposed link will motivate the collection of high-resolution field data that better constrain the timing of volcanism in the Mediterranean, along with the development of novel approaches for coupled lithosphere–magma dynamics.”
Out of this age of crisis, a book has just been published that aims at fully opening the doors of imagination to show how audacious we humans are when in need to restart from scratch:
The book includes an article by the editor Ricarda Vidal (King’s College London) giving an updated perspective on the Atlantropa Project(1929). Atlantropa intended to reduce the area of the Mediterranean Sea by 30% by damming the Strait of Gibraltar, allowing natural evaporation to lower the sea level by a couple of hundred meters. With this project, Herman Sörgel sought to control the inflow of Atlantic seawater to generate electricity, to exposing new inhabitable land (former submarine continental shelf), and to use the Nile River to irrigate a vast part of the Sahara Desert.
The project thus aimed at mimicking what nature did 6 million years ago during the Messinian Salinity Crisis, and that's why I coauthor with Vidal a second chapter dealing with what we know about this ancient salinization and desiccation of the Mediterranean from a scientific perspective, and about the footprint this geology left in western culture.
The rest of the volume discusses fascinating Alternative Worlds including seasteads, planned cities, the high-rise age, and the promising worlds-to-be in the outer space.
Part I: Shaping the Earth and Sea
1. Ricarda Vidal: Atlantropa: One of the Missed Opportunities of the Future
2. Daniel Garcia-Castellanos/Ricarda Vidal: Alternative Mediterraneans Six Million Years Ago: A Model for the Future?
3. Philip E. Steinberg/Elizabeth A. Nyman/Mauro J. Caraccioli: Atlas Swam: Freedom, Capital and Floating Sovereignties in the Seasteading Vision
Part II: The 1960s – Building the Future
4. Patricia Silva McNeill: The Last ‘City of the Future’: Brasília and its Representation in Literature and Film
5. Elena Solomides: The Post-War High-Rise: Promise of an Alternative World
6. Christopher Daley: ‘The landscape is coded’: Visual Culture and the Alternative Worlds of J.G. Ballard’s Early Fiction
Part II: Alternative Lives
7. Maya Oppenheimer: Designed Surfaces and the Utopics of Rejuvenation
8. Boukje Cnossen: The Alternative World of Michel Houellebecq
9. Susanne Kord: From the American Myth to the American Dream: Alternative Worlds in Recent Hollywood Westerns
10. Marjolaine Ryley: Growing up in the New Age: A Journey into Wonderland?
Part IV: Outer Space
11. Peter Dickens: Alternative Worlds in the Cosmos
12. Ingo Cornils: Between Bauhaus and Bügeleisen: The Iconic Style of Raumpatrouille (1966)
13. Rachel Steward: Blue Sky Thinking in a Post-Astronautic Present.
Alternative Worlds, Blue-Sky thinking since 1900, R. Vidal & Cornils (Peter Lang Publishing, Bern, ISSN 3034317875, 9783034317870).
R.B. Cathcart, "What if We Lowered the Mediterranean Sea?", Speculations in Science and Technology, 8: 7-15 (1985).
Let me tell a story about serendipity in research, a story that involves abrupt changes in the Earth's landscape and a 5-million-year-old flood of unprecedented scale.
Classical authors such as Aristotle, Galileo, or Leonardo da Vinci, used to describe the birth of the Mediterranean Sea as an enormous flood through the Strait of Gibraltar that filled a desiccated basin. These stories trace back to the oldest known encyclopedia: Plinius' Historia Naturalis (1st century AD). In its 3rd volume, Plinius the Elder recounted a legend from southern Hispania that attributed the formation of the Strait of Gibraltar to Hercules, the god who "allowed the entrance of the ocean where it was before excluded". The Atlantic Ocean flooding a desertic Mediterranean Sea at epic scales. Amazingly enough, the geophysical and geological research carried out in the last decades seems to suggest that this ancient vision may be quite appropriate.
Since the identification of vast salt strata throughout the Mediterranean by Austrian naturalist Karl Mayer (late nineteenth century) we know that the marine connections between this sea and the Atlantic Ocean became small by the end of the Miocene, during a period known as the Messinian age. Modern chronostratigraphy has dated this at 6 to 5.3 million years ago, around the time when our earliest hominin ancestors started walking on two legs in Central Africa. As a result, the Mediterranean became a huge salt pan that accumulated about 10% of the salt dissolved in the world's oceans, during the so-called Messinian salinity crisis. The ongoing tectonic uplift of the Gibraltar Arc region finally emerged the last Atlantic seaway and isolated completely the Mediterranean from the ocean, about 5.6 million years ago. The Mediterranean then became largely evaporated as a result of the dry climate of its watershed. Finally, about 5.3 million years ago the Mediterranean was refilled from the Atlantic through the Strait of Gibraltar. The indications that this occurred geologically very fast (namely, the abrupt change from Miocene to Pliocene sedimentary layers) made this event be known as theZanclean flood.
Simulation of the refill through the strait of Gibraltar
by Steven N. Ward (Univ. California).
Note the water velocity distribution around 1:27.
Geological map of the Gibraltar strait locating the
erosion channel (red) observed with geophysical
methods.
The flood along the Gibraltar threshold may have been caused by its subsidence below the Atlantic level, or by faulting, or by erosion (or a combination of these three proposed mechanisms). But beyond the causes for the flood, another key unknown is the abruptness and evolution of the flood itself: From the sharp transition in the sedimentary layer record, it is widely thought (though not unanimously) that the event was very fast. But in geology fast can mean a hundred thousand years. Because little was known about its dynamics, and perhaps because for geologists rapid major events are rare and challenge the principle of uniformitarianism, the flood duration underwent a wide range of estimations from tens to tens of thousands of years.
Before knowing anything about the Messinian Mediterranean, I used to model the evolution of landscape over geological time scales, particularly interested on the role of lakes in controlling the long-term evolution of topography of large continental regions.
Lakes are those water bodies collecting precipitation in local topographic minima (yes, this sounds a bit Sheldon-like). Lakes are usually ephemeral over geologic timescales: Unless there are vertical tectonic motions enlarging the topographic basin, they soon fill up with sediment, overspilling their banks. When the water finds a way out, it incises along the outlet, drawing the lake's level down, and propagating this erosion upstream into the lake. In our landscape evolution models this transition was systematically very fast, but this result was not convincing enough for two reasons: First, lake data to compare with were scarce, and we were in the need of a large case scenario where traces of erosion were more evident. Secondly, our models where not accounting for transitory water flow, but instead it was calculating a steady flow (i.e., the water precipitation equals the water losses through evaporation at each time step of the simulation).
2D simulation of the evolution of a tectonic lake
formed in front of a growing tectonic barrier.
The lake evaporates the water collected from
the left side. When the barrier stops growing,
its erosion leads to a sudden capture of the lake.
Then I accidentally learned about the Messinian salinity crisis, about its impact in the Mediterranean evolution, and about the megaflood hypothesis for its ending. It struck me that the feedback between water flow and incision we envisaged for lakes should be similar during the Zanclean flood, taking the global ocean as a huge lake on the verge of overtopping towards the dry Mediterranean. Combining the formulation of river incision with the proper hydrodynamic equations, we built a simple but robust mathematical formulation for overtopping outburst floods. We used then erosional parameters derived from the study or mountain river incision, and then incorporated a reconstruction for the Mediterranean seafloor geometry. Then we started running virtual floods.
The first results were so surprising that we thought something was probably wrong with the code. Things were happening much faster than in those lake scenarios we were used to. Because in the Zanclean flood the source is virtually infinite, the Mediterranean was filling in only a few years along a large erosion channel excavated across the Strait of Gibraltar, some hundred meters deep. Unfortunately, the results were strongly dependent on a parameter that is badly constrained: the erodibility of rocks. But if that was correct, we should be able to find traces of the flood erosion preserved under the sedimentary layers in the strait.
Dry Mediterranean, by Roger Pibernat.
So we turned towards previously published research, finding two other pieces of evidence: The first was a vintage seismic image showing a cross-section of the sedimentary layers near the strait area (Campillo et al., 1992). It showed a clear channel running west to east from the strait into the Alborán Sea, carved in the pre-Messinian sediments. The channel had previously been thought to be the result of river erosion of the dried-up strait, but there’s no obvious large river that could have produced that erosion. The second piece of evidence came from cores of rock drilled from the strait area as part of the exploration for the Africa-Europe tunnel project that would build a train connection between Spain and Morocco (Blanc, 2002). These cores also showed a channel deeper than 200 m, wider than 3 km, and filled with post-Messinian sediment. Altogether, the documented erosion valley connecting the Eastern Atlantic to the Western Mediterranean is more than 200-kilometre long. If this were a result of fluvial erosion, it would be strange to find erosion on both sides of the present water divide between Atlantic and Mediterranean. Furthermore, rather than a waterfall over the Gibraltar Strait as previously suggested, the seismic data show a huge ramp, several kilometres wide descending rather gradually from the Atlantic to the Mediterranean.
With these data, we turned again to the models. Using the observed erosion depth and width as a constrain, the model estimated now that the flood may have began slowly, taking up to several thousand years before a significant rise in Mediterranean level occurred. But importantly they also show that 90% of the water must have entered in a period shorter than two years, and that at the peak discharge, water poured in at a rate of 100 million cubic meters per second, about a thousand times the largest river on Earth today. If 'harder' erosion parameters were used, then the refill of the Mediterranean would be predicted to be slower, but the calculated erosion at the end of the flood would be insufficient to reproduce the geophysical images. To fit the observations, the flooding channel had to cut down into the bedrock almost half a meter per day, leading to a large inlet flow that would increase the Mediterranean sea level by more than 10 meters per day.
The technique does not allow constraining the speed of the initial stages, nor the mechanisms involved in triggering the flood. This means that the initial trigger may have been a geologically modest event such a large storm, a tsunami, or a partial collapse of the dividing barrier. What the results do ensure is that in order to account for the final size of the erosion channel, 90% of the water must have been rapidly transferred in a period ranging from a few months to two years.
Possible evolution of the flood derived from the model. The lower panel shows the evolution of the seaway depth as it is eroded by the increasing flow of water (black lines, left scale) and the rising Mediterranean level (red lines). From our article in Nature.
If these observations and calculations are independently confirmed, the Zanclean flood would become the largest known flood on Earth's history. The Zanclean flood involved an order of magnitude more water flow than the megafloods that we know took place during the last deglaciation (e.g., the Missoula floods or the Bonneville flood).
The implications of such a rapid flooding are inevitably big, as a large number of multidisciplinary studies have documented: Global flora and fauna had to adapt to the new
environmental conditions rapidly. Marine species colonized a huge new realm rapidly whereas for land species, particularly in islands, the flooded
Mediterranean became a sudden barrier triggering speciation. Had the land connection remained, it could have facilitated an earlier arrival of early humans in western
Europe. Instead early humans had to take a circuitous route to Western
Europe and didn't arrive until 1.5 million years ago. The Messinian salinity crisis also highlights the importance of seaways in understanding the geological record: straits limit the mix with the global ocean and their size is the key parameter modulating the chemical registry found in sediment. The flood may also have had tectonic implications: The weight of the flooding waters is such that it should have modified the rotation of the Earth, and it should have made the entire Mediterranean region sink by at least one kilometer in the mantle, according to the principle of Isostasy. Also global climate surely must have been impacted by the Messinian salinity crisis and its rapid ending, but so far this is perhaps the most elusive aspect of the crisis, something remarkable since I am not aware of other scenarios in geological history where the climatic response to such a large environmental change can be better tested.
So there are plenty of open questions on the Zanclean Flood that need an answer. More pending Retos Terrícolas.
Video on the Atlantropa Project, showing the collapse of a
projected dam across the Strait of Gibraltar.
[This is related to research of our own group here at CSIC, as published inthis article]
[This post has been published in Mapping Ignorance]
References:
Blanc, P.-L. The opening of the Plio-Quaternary Gibraltar Strait: assessing the size of a cataclysm, Geodin. Acta 15, 303—317 (2002).
Campillo, A., Maldonado, A. & Mauffret, A., Stratigraphic and tectonic evolution of the western Alboran sea: Late Miocene to recent, Geo Mar. Lett., 12, 165– 172 (1992).
Garcia-Castellanos, D., 2006. Long-term evolution of tectonic lakes: Climatic controls on the development of internally drained basins. In: Tectonics, Climate, and Landscape evolution. Eds.: S.D. Willett, N. Hovius, M.T. Brandon & D.M. Fisher. GSA Special Paper 398. 283-294. doi:10.1130/2006.2398(17) [pdf]
Garcia-Castellanos, D., F. Estrada, I. Jiménez-Munt, C. Gorini, M. Fernàndez, J. Vergés, R. De Vicente, 2009. Catastrophic flood of the Mediterranean after the Messinian salinity crisis. Nature 462, 778-781 doi:10.1038/nature08555 [pdf]
[1st chapter of this post (1/3)] [2nd chapter of this post (2/3)] [Spanish version of this post]
In two previous parts of this post I tried to summarize the evolution of the Messinian salinity crisis, the period of widespread salt precipitation in the Mediterranean. This 3rd part focuses on our own research, aiming at finding a mechanism to explain the long first evaporitic phase (Stage 1).
A key unknown that must be mentioned in advance is the depth of the last seaway that allowed the inflow of Atlantic water, the water that replaced the evaporation at the surface of the Mediterranean sea. Hydraulic calculations indicate that a too-shallow seaway (less than ~10 meters deep) would imply a reduction in Atlantic water supply and a drawdown of the Med's level (it would literally evaporate). In contrast, a seaway that was too deep (more than ~30 m) would allow too much mixing between both sides, contradicting the observed salt precipitation. Only intermediate values could allow uninterrupted salt precipitation during the first stage of the Messinian salinity crisis. But, how could the seaway keep in that narrow range of depths when global sea level changes are known to oscillate by several tens of meters? (See fig.3)
1. Cartoon of the detachment and lateral tear propagation
of a dense piece of lithosphere under the Betic
Cordillera. Yellow arrows indicate forces related
to the weight of the slab; white arrows show
vertical motions induced by the tear propagation.
One key obstacle to tackle this question is the lack of good constrains as to which was the last corridor connecting both sides of the Gibraltar Arc. There were several seaways crossing the Betics and the Rif, and all of them closed between 7 and 6 million yrs ago. These corridors are recorded in marine sediments showing paleocurrents and laying today several hundred meters above sea level. But the dating methods have been so far unsuccessful to resolve which was the last one to feed the Med with relatively fresh water.
2. Geological map of the Betics and the Rif (S Spain, N Morocco) combined with tomographic images of the Earth's interior, reaching a 660 km depth. The vertical white arrows show the crustal uplift inferred from the altitude of marine sediments of early Messinian age.
As for the mechanism responsible for the uplift itself, hints come from isotopic analyses and datations of the volcanism in the Alborán Sea (Duggen, 2003), together with the images obtained via seismic tomography of the Earth's mantle structure. These suggest that the uplift and shrinkage of the seaway may have taken place by a known geological process: due to the detachment of a dense piece of lithosphere (slab break-off). The tomographic images (see figure) use the arrival time of earthquake waves to derive the internal structure of the Earth, and show a lithospheric slab detaching from the Earth's crust underneath the Cordillera Bética. As this body sunk in the upper mantle, it would tear apart (slab tear) and trigger an isostatic rebound of the overlaying Earth's crust. This could explain the uplifted marine sediments in the Betic and Rif cordilleras, providing the uplift rates needed for the closure of the seaways.
3. Sea level changes in the last 8 million years (data from Miller & coauthors, 2005, Science, based on the oxygen isotopic content). The three red dots indicate the initiation of Stages 1 and 2, and the final reflooding of the Mediterranean (ages from Krijgsman et al., 1999).
But coming back to the essential problem of the mechanisms behind the salinity crisis: Tectonic processes as those discussed above are slow: to produce vertical motions of a few hundred meters they need at least hundreds of thousands of years. But sea level (see figure) changes by tens of meters in periods of a few thousand years. How could then the gateway remain in such a narrow depth range for more than 100,000 years? What kept the seaway neither too deep, nor too shallow in spite of the global sea level variations?
4. Cartoon illustrating the competition between the tectonic uplift of the seaway and its erosion due to the water flow feeding the Mediterranean (Garcia-Castellanos & Villaseñor, 2011).
Our study (Garcia-Castellanos & Villaseñor, 2011) is based on relatively simple hydrodynamic calculations combined with erosion formulations that had been previously used for landscape modeling and river erosion studies. The results of combining these techniques to simulate the channel connecting the Mediterranean and the Atlantic show that the rate of erosion produced by the incoming waters that compensated the Mediterranean evaporation was similar to the tectonic uplift rate presumed for the Gibraltar Arc, suggesting that uplift and erosion may have been in equilibrium for a long period, keeping the connecting seaway at an approximately constant depth. The results also show that global sea level changes could also have been accommodated by erosion to some extent.
5. Two simulations as example. Dark lines show an evolution for a slow uplift (red for sea level; black for seaway depth), whereas the light lines are for a fast uplift. In both an equilibrium between erosion and uplift is reached, but the equilibrium decrease of the Mediterranean level required for the slow uplift is smaller than for the rapid uplift. The total amount of inflowing water is in both cases identical, the one that compensated the hydrological déficit of the Med (Garcia-Castellanos & Villaseñor, 2011).
The model also predicts that this competition between uplift and erosion should normally occur out of phase, because the evaporation in the Med needs some hundreds or thousands of years to make the level fall. As a result, a cyclicity in terms of sea level and salt precipitation is predicted that could explain the intriguing cycles observed in the salt deposits all around the coast.
Global sea level fluctuations probably competed with the tectonic uplift by modulating the erosion rates exerted by the overtopping atlantic waters into the Mediterranean (see the supplementary information in the original publication).
Results from the model:
6. Equilibrium level of the Med as a function of the uplift of the seaway.
A possible summary (or the simplest one supported by our results) consists of 4 stages (dates from Krijgsman et al., 1999):
Stage 0 (before 5.96 million years BP). The Betic-Rifean island arc rose, shrinking the connections between Mediterranean and Atlantic.
Stage 1 (5.96 Ma - ?). A last connection allows the inflow of Atlantic water, and erosion along this enters in competition with uplift, keeping the inflow roughly constant. The Mediterranean level descends some tens or hundreds of meters but it becomes quickly a saturated brine.
Stage 2 (? - 5.33 Ma). Tectonic uplift exceeds seaway erosion and eventually disconnects the Mediterranean from Atlantic water supply. The Mediterranean goes dry, its level drops by 2 km.
Stage 3 (5.33 Ma). The level of the Atlantic exceeds that of the Gibraltar land bridge and triggers a fast refill of the Med.
7. Cartoon of the simplest evolution suggested for the Messinian Salinity Crisis from the modeling results. Stage one corresponds to a cancellation of the outflow from the Med to the Atlantic; Stage 2 is the presumable desiccation starting when the threshold of the seaway becomes above sea level; The Zanclean flood is the refill triggered as the Atlantic waters found a way over the lowest sill of the Gibraltar ARc.
The mechanism we propose for Stage 1 implies that the last corridor should undergo some hundred meters of erosion, carving a gorge while the surrounding mountains where rising. Finding this gorge nowadays won't be easy, since it has been probably overprinted by the landscape erosion taking place in the 6 million years passed since.
8. Salinidad actual de la superficie de los oceános. La mayor salinidad del Mediterráneo se debe a la mayor evaporación e insolación isolation de sus aguas. Source: World Ocean Atlas2005
These findings and the extreme geological conditions imposed during th MSC period may help to understand the global change in response to abrupt environmental changes. Since the Mediterranean trapped about 10% of the global ocean salt in at least 100.000 yrs and probably underwent desiccation afterwards, the effects of this should be visible in the biology and climate, perhaps at a global scale. The migration of mammals using the new land bridge formed when the last corridor closed (including African camels that moved to near Valencia, for example) is well documented by paleontologists. But the impact in climate is more elusive from the observational point of view. If climatic data of the multi-million-year time-scale improve, they could allow a better calibration of the multiple parameters of global climatecomputer models. The desiccation of the Mediterranean offers a unique scenario, a natural laboratory for that calibration, and hence it may help to improve existing climatic models.
9. Artístic view of the surface and underground events during the early stages of the Mediterranean isolation.
Update: The impact of the Messinian Salinity Crisis in exploration and Mediterranean resources will be the focus of a session at the forthcoming AAPG Conference in Barcelona, Spain, April 8-10, 2013 http://www.aapg.org/barcelona2013/
References:
Krijgsman, W., Hilgen, F., Raffi, I., Sierro, F., & Wilson, D. (1999). Chronology, causes and progression of the Messinian salinity crisis Nature, 400 (6745), 652-655 DOI: 10.1038/23231
Duggen, S., Hoernle, K., van den Bogaard, P., Rüpke, L., & Phipps Morgan, J. (2003). Deep roots of the Messinian salinity crisis Nature, 422 (6932), 602-606 DOI: 10.1038/nature01553
Garcia-Castellanos, D., Estrada, F., Jiménez-Munt, I., Gorini, C., Fernàndez, M., Vergés, J., & De Vicente, R. (2009). Catastrophic flood of the Mediterranean after the Messinian salinity crisis Nature, 462 (7274), 778-781 DOI: 10.1038/nature08555
Garcia-Castellanos, D., Villaseñor, A. (2011). Messinian salinity crisis regulated by competing tectonics and erosion at the Gibraltar arc Nature, 480 (7377), 359-363 DOI: 10.1038/nature10651
Govers, R. (2009). Choking the Mediterranean to dehydration: The Messinian salinity crisis Geology, 37 (2), 167-170 DOI: 10.1130/G25141A.1
Garcia-Castellanos D, Villaseñor A (2011). Messinian salinity crisis regulated by competing tectonics and erosion at the Gibraltar arc. Nature, 480 (7377), 359-63 PMID: 22170684
