Sea level in the Mediterranean Sea.

[studiot]

According to the BBC, (Iain Stewart The Power of the Planet) the rate of evaporation in the Med is greater than the replacement water supply from the incoming rivers.

 

That the sea level in the Med is currently not changing is due to inflow of water from the Atlantic, through the Pillars of Hercules.

They also state that this inflow is only just enough to accoplish this at present.

 

So if there is a local average temperature rise due to global warming will the increased rate of evaporation raise or lower sea levels in the Med?

 

I understand that the salt deposits and fossil remains show that the Med has dried, perhaps altogether out in not too distant previous times.

[Acme]

Interesting topic.

...So if there is a local average temperature rise due to global warming will the increased rate of evaporation raise or lower sea levels in the Med? ...

I think the answer is a big 'it depends'. What it depends on is how the increase in temp affects the surrounding areas that contain the river systems that feed the Med, as well as how the local temp rise affects precipitation falling directly into the sea. As we are already seeing, the global climate change is producing more frequent and larger storms in some areas and droughts in others.

 

Then too, local conditions are not always completely responsible for local effects as we saw this week in the US when the typhoon in Japan changed the path of the jet stream and we had unseasonably cool weather dip into the upper Midwest and Northeast.

 

All this is of course off-the-cuff and if you'd like I can seek out some references in support of my sleeve.

[Ophiolite]

Yes, the Mediterranean was a harsh world of hot, arid salt flats, with - perhaps - some highly saline lakes, during the Miocene. River input was even less then than today. The major cause was the tectonic closure of the Straits of Gibraltar. When they reopened the Mediterranean refilled. Now that would have been a waterfall!

[Acme]

Yes, the Mediterranean was a harsh world of hot, arid salt flats, with - perhaps - some highly saline lakes, during the Miocene. River input was even less then than today. The major cause was the tectonic closure of the Straits of Gibraltar. When they reopened the Mediterranean refilled. Now that would have been a waterfall!

A doozy of a waterfall! Even today the Med is saltier than the Atlantic and in fact this saltier water is outflowing at Gibraltar in a layer below the less-salty inflowing Atlantic water.*

 

*Strait of Gibraltar @ ESA

 

I can't help but wonder what ruins & shipwrecks would be revealed if the Med's level dropped a hundred meters or so. Alas it looks like that would take a rather sizeable seismic event to close the gap.

This paper suggests reduced precipitation and increased winds as major contributors to an increase in salinity and the drop in Mediterranean Sea levels since ~ 1960.

 

Full paper: >>Sea level drop in the Mediterranean Sea: An indicator of deep water salinity and temperature changes?

Abstract.

Coastal sea level data from seven tide gauges in the Western Mediterranean and the Adriatic show decreasing sea levels after 1960. Control stations in the Black Sea and in the northeastern Atlantic indicate sea levels still rising after 1960. The sea level trend in the Mediterranean before 1960 was between 1.2 and 1.5 mm yr^{- 1}, while in the Atlantic and the Black Sea stations it was between 1.8 and 2.2 mm yr^-1. After 1960 the sea level in the Mediterranean is decreasing with rates up to -1.3 mm yr^-1, while in the Black Sea the sea level trend remains unaltered and at the Atlantic stations sea level keep rising with reduced rates of 1.0-1.2m m yr^-1. The change of the Mediterranean sea level trends, which is in excess of the sea level trend reduction at the Atlantic sites, is consistent with increases in temperature and salinity of the Mediterranean Deep Water. The reduction of sea level trends at the Atlantic sites is probably related to the North Atlantic Oscillation.

[Essay]

Yes, the Mediterranean was a harsh world of hot, arid salt flats, with - perhaps - some highly saline lakes, during the Miocene. River input was even less then than today. The major cause was the tectonic closure of the Straits of Gibraltar. When they reopened the Mediterranean refilled. Now that would have been a waterfall!

Like a ball hitting the floor, Africa seems to have "bounced" off of the European plate (or vice versa) about 40 times, before settling down.

 

"Late Miocene salt deposits in the western Mediterranean indicate that the Mediterranean completely desiccated... ...about 40 times in the latest Miocene, withdrawing about 6% of the salt from the world's oceans (Ryan 1973). The net reduction in average ocean salinity by about 2.0% may have had a significant effect on ocean circulation." -p.201

 

from: Oxford Monographs on Geology and Geophysics no.16; Paleoclimatology; Crowley & North; 1991.

 

Note also:

"If the Straights of Gibralter were closed today, the Mediterranean would dry up in about 1000 years...." -p.201

"Since the Mediterranean deposits are 2-3 km thick, and only 70 m of salt would be produced by isolation if it happened just once, the cycle of evaporation must have been repeated about 40 times...." -p.201

===

 

Though I'd be happy to hear of any updates on this 1991 information.

 

~

[studiot]

Thank you all for your responses.

 

Acme

What it depends on is how the increase in temp affects the surrounding areas that contain the river systems that feed the Med,

 

Something I hadn't considered, good point!

 

However, today's weather and climate calculations depend upon adding together contributions from all the areas around the globe. I don't know if warming cooling models are capable of doing this into the future, but the results would certainly be of more interest to the local population than an it depends statement.

 

Ophiolite

The major cause was the tectonic closure of the Straits of Gibraltar

 

Yes the series discusses this as part of the presentation.

 

 

Essay

General

 

Thanks for the references.

 

One further consequence is said to be in the fossil record, particularly the pygmy elephants. There is also some spectacular video of the salt caves.

[barfbag]

Dang! I thought for sure this would be another GW thread discussing rising sea levels.

 

It is interesting though and makes you wonder how GW can threaten many communities with rising water and yet the Mediterranean might be lowering in sea level. It seems to defy logic like taking trying to take the water out of the right side of your cup without affecting the water level on the left side.

 

I wonder if this could be measured or predicted by measuring the increases in current in the strait of Gibraltar/Nile.

[Roamer]

 

 

That the sea level in the Med is currently not changing is due to inflow of water from the Atlantic, through the Pillars of Hercules.

They also state that this inflow is only just enough to accoplish this at present.

 

Would this inflow not increase as soon as the sea level of the Med lowers ?
(and vice versa off course)

[CaptainPanic]

Would this inflow not increase as soon as the sea level of the Med lowers ?

(and vice versa off course)

 

Yes, the Mediterranean will only dry up if the inflow through the strait of Gibraltar is somehow stopped.

 

Frankly, even if some major tectonic event would block it, I think we (humans) would quickly re-open it by just blowing up that blockage. It's just too important economically, as can be seen in the picture below of the world's shipping lanes.

[cnewton]

Like a ball hitting the floor, Africa seems to have "bounced" off of the European plate (or vice versa) about 40 times, before settling down.

 

"Late Miocene salt deposits in the western Mediterranean indicate that the Mediterranean completely desiccated... ...about 40 times in the latest Miocene, withdrawing about 6% of the salt from the world's oceans (Ryan 1973). The net reduction in average ocean salinity by about 2.0% may have had a significant effect on ocean circulation." -p.201

 

from: Oxford Monographs on Geology and Geophysics no.16; Paleoclimatology; Crowley & North; 1991.

 

Note also:

"If the Straights of Gibralter were closed today, the Mediterranean would dry up in about 1000 years...." -p.201

"Since the Mediterranean deposits are 2-3 km thick, and only 70 m of salt would be produced by isolation if it happened just once, the cycle of evaporation must have been repeated about 40 times...." -p.201

===

 

Though I'd be happy to hear of any updates on this 1991 information.

 

~

 

Ok, it is obviously a flawed estimate. Hopefully it has long been since changed. Yes, it could happen that the connection closed 40 times. Far more likely is that it almost closed and became a one way trip for incoming water a few times. Right now the Strait of Gibraltar is so deep that it has large enough Reynolds number to allow two way flow of water in (salty) and out (more salty). Black Sea is the same. But in Caspian Sea, there was at least recently a lagoon that became landlocked except a river like flow.

 

http://en.wikipedia.org/wiki/Garabogazk%C3%B6l

 

This can go on indefinitely until the whole lagoon becomes filled with salt, or Caspian Sea runs out of salt as case may be. In the case of the Mediterranean, the oceans may not have enough salt to fill the sea, as it is a couple miles deep and huge. Some one else can do the math. So it could have closed only one time, though gradually enough to concentrate much salt and precipitate it out (only about 1/4 of the water content can be table salt before precipitation to the bottom or edges, iirc).

 

What is known is that huge salt flats developed and were covered by sediments, effectively sealing them under the ocean (like much of the Siberian Arctic Ocean covers a continental shelf that is thick with buried ice). The drilling teams found that in the 1960's as well as huge canyons in the delta sediments of the Nile and all the way up beyond the Aswan dam hundreds of miles upstream. So it did not indefinitely have a slow input.

 

 

>>

A doozy of a waterfall! Even today the Med is saltier than the Atlantic and in fact this saltier water is outflowing at Gibraltar in a layer below the less-salty inflowing Atlantic water.*

 

More recent information has pretty much disallowed this. The waterfall is either completely buried or non existent. From what I read, the current thought is that the gradient was so slight that it never scoured the bottom much before closing enough to carve canyons into the continental slope or shelves in the Mediterranean basin at the believed points of entry around Cartegena and Valencia. Considering you have a hundred miles and a gradient of maybe 20 feet, it could be a lazy flow down a huge Amazon. The flow was so broad and shallow, maybe 50 miles wide and a hundred miles long, that it never scoured enough to widen the flow. If tides were substantial at the inlet, then a huge tidal area would also cover up incipient little canyons. Land raised before that happened, again since it was so broad it happened gradually. Sorry. I wish it had a huge cataract as well.

[studiot]

Thanks for the additional info cnewton.

[Wild Cobra]

Yes, the Mediterranean was a harsh world of hot, arid salt flats, with - perhaps - some highly saline lakes, during the Miocene. River input was even less then than today. The major cause was the tectonic closure of the Straits of Gibraltar. When they reopened the Mediterranean refilled. Now that would have been a waterfall!

 

I have often wondered if that was part of Noah's flood.