An interesting point, widely forgotten, or ignored, by the folks in a panic over arctic ice, is that we’ve not always had them. They come, they go. Life goes on.
I was looking up something else, having to do with Egypt, and ended up looking at the tendency of the entire Mediterranean Sea to come and go. So all the folks in a panic over a little sea level variation maybe ought to also think about how nature periodically erases the entire Mediterranean. Then puts it back.
Realize, too, that this isn’t exactly happening in ‘deep time’. Long long ago, yes. But we’re not talking Billions of years here. More like 5 Million. (As humans started evolving a distinct line about 6 Million Years Ago, this sort of matters to us. We humans WERE around then, just in the south of the Nile system, and changes in the Mediterranean and Nile would have chosen our destiny.)
The Messinian Salinity Crisis (MSC), also referred to as the Messinian Event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partly or nearly complete desiccation throughout the latter part of the Messinian age of the Miocene epoch, from 5.96 to 5.33 Ma (million years ago). It ended with the so-called Zanclean flood, when the Atlantic reclaimed the basin.
What I found interesting about this was the probable cause, and the state of the world oceans at the time. First, the likely cause is that the Strait Of Gibraltar is not stable, in geologic terms. It just so happens that Africa is slamming into Europe from the south. So land ‘around there’ gets thrust up in some places, buckled under in others; and, it would seem, wobbles back and forth in the Strait opening and closing the spigot from time to time.
This party interested me as one of the loose ends in the Atlantis description, from Plato, is a discussion of somewhere near the gate to the ‘true ocean’ that at one point was shallow and not navigable, but then at others had become navigable again. Could it be that they had a history of Gibraltar in mind? So I keep my eyes open for things connected to that. While I doubt that the Strait Of Gibraltar wobbled open / closed during the times just before Plato, the simple fact is that they were describing a history from ancient records that might have gone back tens of thousands of years. ( We now know there WERE civilizations 12,000 years ago, and perhaps more.)
So one question that comes to mind is just “Might there be short term oscillations of the Strait Of Gibraltar that are not enough to evaporate the Mediterranean, but enough to change navigability and account for the Plato description?”
I have no answer on that. Not sure how to get one either. A “shut” straight that then reopened could easily have the witness sediments washed away in the reflooding event. As there are heavy currents in the straight, one would likely need to find indirect indications of active vs inactive water flows.
But on to the second bit.
Further down that analysis of the evaporative cycles of the Mediterranean, it says:
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, there is now a scientific consensus that global sea level fluctuations cannot have been the major cause, although it may 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
Oh Dear! NO Ice caps?
So let me get this straight: There were NO ice caps during a critical evolutionary part of human development. We had bears and penguins and all survive quite nicely then, too? OK…
That makes it look, to me, like the folks in a panic about polar ice can choose either to accept that the history of the Mediterranean Sea is correctly understood, or that they are in a panic about not very much at all with respect to living things. (Yes, it would be a mess for coastal cities).
Heck, we had the entire Mediterranean Sea evaporating and returning, several times. I think that shows life can adapt to a little change in ocean hight. And the climate will have swung dramatically with the massive water, water vapor, and temperature moderating changes.
The water from the Mediterranean would have been redistributed in the world ocean, raising global sea level by as much as 10 m (33 ft). 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.
So some geological shifting can happen (has happened many times) and the global sea level can be modulated by 10 m or 33 feet? The entire freeze / thaw cycle can be shifted by salinity changes? Oh Dear! Talk about your climate change!
How fast though? Surely the entire Mediterranean can’t just go “poof!” very fast?!
Even now the Mediterranean is saltier than the North Atlantic because of its near isolation by the Strait of Gibraltar and its high rate of evaporation. If the Strait of Gibraltar closes again, which is likely to happen in the near geological future (though extremely distantly on a human time scale), the Mediterranean would mostly evaporate in about a thousand years. After that, continued northward movement of Africa may obliterate the Mediterranean: see Mediterranean Ridge.
So it’s likely to happen again, too. Hmmmm….
The Mediterranean Ridge is a wide ridge in the bed of the Mediterranean Sea, running along a rough quarter circle from Calabria, south of Crete, to the southwest corner of Turkey, and from there eastwards south of Turkey, including Cyprus.
It is caused by the African Plate subducting under the Eurasian and Anatolian plates. As the African Plate moves slowly north-northeastward, it is plowing up the igneous and sedimentary rocks of the Mediterranean seafloor, lifting them from the seabed creating Cyprus and other islands along the ridge.
Along the ridge have been found five deep basins full of anoxic brine where Messinian evaporite deposits of brine caught up in this ongoing orogeny have dissolved
So right now the African plate is squishing into Greece and Turkey a bit more, but in the past the pivot has had the Strait of Gibraltar close or open. At any time, this can shift a bit one way or the other and the Mediterranean becomes a distant memory in less time than the Roman Empire took to go from new to collapse.
Things that make you go “Hmmmmm….”
Oh, and the ice caps can all go away entirely and not change this, nor do much to stamp out life on the planet.
Things you can learn from a bit of salt… Guess it pays to be a ‘Salty old dog’ ;-)
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 (see, e.g., van Dijk et al. (1998)).
In any case, the causes of the closing and isolation of the Mediterranean Sea from the Atlantic Ocean must be found in the area where nowadays the Strait of Gibraltar is located. In that area, one of the tectonic boundaries between the African Plate and the European Plate and its southern fragments such as the Iberian Plate, is located. This boundary Zone is characterised by the presence of an Arc Shaped tectonic feature, the Gibraltar Arc, which includes southern Spain and northern Africa. In the Present Day area of the Mediterranean Sea, three of these Arc shaped belts are present: the Gibraltar Arc, the Calabrian Arc, and the Aegean Arc. The kinematics and dynamics of this Plate Boundary and of the Gibraltar Arc during the late Miocene are strictly related to the causes of the Messinian Salinity Crisis: Tectonic reconfiguration may have closed and re-opened passages; the region where the connection with the Atlantic Ocean was situated 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. An extensive discussion can be found in Weijermars (1988)
The Gibraltar Arc is a geological region corresponding to an arcuate orogen surrounding the Alboran Sea, between the Iberian Peninsula and Africa. It consists of the Betic Cordillera (south Spain), and the Rif (North Morocco).
Maximum altitudes of the region are reached at the Mulhacén peak (3482 m) at the Cordillera Betica. Precipitation is collected mainly by the Guadalquivir (Betics) and Sebou (Rif) rivers, which have delivered most sedimentary infill of the homonym sedimentary foreland basins.
The geology of this orogen undergoes simultaneous extension coeval to the regional convergence between Iberia and Africa during the Tertiary, which has not yet been satisfactorily interpreted.
For those not familiar with the word, an ‘orogen’ is the stuff that happens when continents collide…
So what this is saying is that we really don’t have a good handle on why the collision of Africa and Europe is being so ‘flexible’ about the opening and closing of The Straight of Gibraltar. (I’d suggest looking at variable ‘rotation’ of Africa and the variations of deformational hardness and uplift of the two ends of Europe).
But the bottom line here is pretty simple. SOMETHING has the Strait of Gibraltar sometimes slam shut, and sometimes open up again. It’s done it a lot in the past. It’s likely to do it again in the future. There’s even a load of sedimentary deposits in Iberia indicating that parts of IT were sometimes below sea level.
And some folks think putting some gas in the air matters in the face of forces like that…
The 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. The basin is filled with turbidites and evaporites of the Tortonian-Messinian ages of the Miocene Epoch.
It is a matter of some debate whether the basin dried out at the same time as the main Mediterranean basins
Notice the large freeway in the lower right and the small houses…
The basin is divided into the following members:
At the bottom of the image, the house is constructed on the steep yellow cliffs of the resistant Azagador member.
The lower (whiter) and upper (yellower) Abad marls, a Tortonian/Messinian series of turbidites featuring pronounced Milankovic (20,000 year precession) cyclicity, allowing chronostratigraphic dating; these fine muds are easily eroded.
When the sea returned overdeepening the basin, salt water waterfalls eroded a 200 m depression patterned by 30 m deep gullies.
the Messinian Yesares member, a gypsum evaporite, forms the steep bluffs at the top of the valley; there is some debate about how conformable its contact with the Abad marls is.
Pliocene deposits, rest unconformably on the top.
Complexity of drawdown and reflooding complicate correlation of the ‘Salinity Crisis’ stratigraphy.
The basin was separated from the main Mediterranean basin during the Messinian salinity crisis; therefore the timing of the Yesares member relative to the main basin evaporites is crucial to distinguish between models of how the Mediterranean dried out.
So we’ve got chunks of Spain, sometimes under the ocean / sea, sometimes dozens (hundreds?) of meters above it Bobbing up and down, and the sea evaporating, and coming back; all while Gibraltar pops open and slams shut again. With ice caps melting, and reforming.
Oh, by the way, those forces have not ended. We just live very short lives and do not notice them happening.
What got me started on this was a satellite image of Egypt. It looks like the Nile Delta was entering a higher Mediterranean at one time. In the context of the above, it is a little bit harder to say if Egypt was lower, or the Mediterranean higher, and what that might say about ocean levels and ice caps… But, for completion, here’s the picture that got me started on this.
You can see the present Nile Delta as a large greenish triangle where it meets the Mediterranean. Now scan just a bit to the left. See that MUCH bigger ‘delta’ shape in the desert sands? See the ancient river channel feeding it that diverges from the present Nile about 2/5 of the way from the top of the image.
What we learn from this image is that either Egypt has risen some, or the Mediterranean was higher some time ago when that ancient delta was doing deposition. Or possibly that the ‘cut off’ of the Nile isolated this fan area with sedimentation. That there is no ‘erosional’ feature between the end of the ancient fan and the present Mediterranean level implies the Mediterranean was high enough to prevent a channel forming, or that it is covered up with new sediments. The far end of it is at near zero (perhaps even below present sea level) so it is a bit unclear where the actual delta ended and sea began. It does strongly suggest, though, that the geology of the area is not very static. If further suggests that to find extraordinarily ancient civilizations, you need to go dig out there, not near the present Nile delta.
Yet the end / edge of that delta being near zero elevation makes it hard to say much about sea level change since that time. Just that big changes do happen there.
An elevation map of Egypt:
So while looking for the Nile connection to Mediterranean levels was interesting, it’s just not as important as the other changes in the Mediterranean. One is, at most, an indicator of broader changes. The other one causes those changes…
One thing this makes very clear, in either case, is that a whole lot of “Climate Change” happened, even during the time of human presence on earth, that had nothing to do with human activity. The Earth Changes. A Lot. All on it’s own.
Update on the Nile
Found this interesting article that lists the various ‘life stages’ of the Nile. It looks rather dynamic.
6 million BCE: The earliest we know of a river through Egypt; scientists name it Eonile. This river ran through a canyon with walls that could be up to 3,000 metres high. There are indications that the Mediterranean Sea did not exist in this period. The source of Eonile is not known.
5 million: The waters of the Mediterranean Sea rises, filling up a basin reaching as far as modern Aswan. This brings an end to Eonile.
4 million: A second river starts flowing through Egypt, by modern scholars referred to as Paleonile. Its sources are believed to have been in equatorial Africa.
1.8 million: Dramatic climatic changes, causing the end of a water stream flowing north. Desertification in North Africa casues the emoty river canal to be filled with sand.
1.5 million: The third river, the Protonile, starts flowing through Egypt, creating many interwoven channels. The Protonile ran to the west of the modern Nile, through the region known today as Western Desert.
500,000: The Prenile replaces the Protonile, running further to the east, and starts carving out the river valley existing today. Its discharge was the largest ever for any of the Niles, before and since.
150,000 The Prenile starts to dry out.
30,000: The Neonile starts flowing through Egypt, basically following the same course as the modern Nile, but with a higher elevation.
8,000: The Neonile has carved itself down to the present elevation, and we can start talking about the Nile as we know it today.
1902: The Aswan Dam opens, allowing better control with the flow and flooding of the Nile through Egypt.
1960: The Aswan High Dam opens, allowing Egypt even better control with the flow all through the year, but removing the valuable silt which normally enriched the soil. A very important hydroelectric power plant is constructed here.
It is worth noticing that those ’3000 foot canyons’ were largely below sea level. The Eonile was cutting a trench as it dumped down into the below sea level depression of the dried out Mediterranean.
Nice write-up of the history of the “Niles”…
So the entire Nile River comes, goes, wanders… All without CO2 doing a thing…