Re: dry Meditteranean

chornedsnorkack_at_hushmail.com
Date: 01/15/05 

Date: 15 Jan 2005 04:52:30 -0800

Aidan Karley wrote:
> In article <cs1bdc$p7p@library2.airnews.net>, Tic wrote:
> > A few years ago, give or take a few million, there was a
land-bridge
> > across the Strait of Gibraltar, and the Mediterranean was closed
off from
> > the Atlantic Ocean. From what I read, the sea-bed was dry at that
time.
> >
> Google "Messanian salinity crisis" (watch my spelling, it's
late
> here!).
>
Preferrably Messinian.

> > What I want to know is, why didn't it fill up and become a
fresh-water
> > sea?
> >
> Precipitation in the hinterland was less than evaporation in
the
> basin. For the Mediterranean, it *still* is, witness the
counter-flowing
> currents of {low density, low salinity} and [high density, high
salinity]
> seawater flowing from the {Atlantic} to the [Mediterranean] through
the
> Straits of Gibralter. Cut off that flow of low salinity water and the

> Mediterranean would dry out in a (geologically) short time.
>
> The Dead Sea is an instructive case in point - more-or-less
the same
> latitude, less water input because further from the ameliorating
effects of
> the Atlantic (storm force 10~11 effects tonight).
>

In geologically short time, but not historically short time.

IIRC, Mediterranean now receives about 30 000 cubic metres per second
of fresh water by rain on the water surface, 8000 -"- by all rivers
directly entering and 5000 -"- from the Black Sea. The evaporation is
around 150 000 cubic metres per second, so 100 000 cubic metres per
second is a shortfall.

The shortfall is compensated by water entering from the Atlantic by
Gibraltar Strait.

Were the Gibraltar Strait suddenly closed again, the level of
Mediterranean would start falling at about 1 metre per year. Which is
about what happens to salt lakes, like Aral Sea or Mono Lake or Dead
Sea if the rivers flowing in are suddenly diverted.

And at 1 metre per year, well, the Mediterranean is about 5000 metres
deep, so it cannot dry up faster than 5000 years. Which is why Mono
Lake, Aral Sea and Dead Sea also still exist.

But before it gets to 5000 metres, other interesting things happen.

For one thing, the shrinking of the evaporating cool sea surface would
alter climate around the sea.

If this were neglected or assumed to make no change to the river
runoff, then the existing rivers would still sustain salt lakes with
total area of several hundred thousands square kilometres. Also, while
part of the rain falling on dried-up seabed would evaporate there, a
part would run off as rivers.

Thus, unless the drying-up of Mediterranean causes the surrounding
areas and watersheds to dry so much that water no longer runs off,
there would remain large lakes at the bottom of the Mediterranean.

Also brine does not evaporate as much as seawater. Saturated sodium
chloride solution - about 35 % - has air humidity of 75 %. At the same
time, seawater - 3,5 % - has air humidity of about 98 % above it. So,
if absolutely dry air encounters brine, the brine can only lose 75% as
much water as fresh or sea water, and generally evaporates considerably
less because the air is not completely dry. In air with humidity of 75
%, brine cannot evaporate at all.

Bitterns, of course, keep air humidity even lower, so evaporate even
less.

Thus, the drying of Mediterranean would not be complete and would take
in the order of 10 000 years to get as far as it ever gets.

Also, Dead Sea valley contains a large freshwater lake - the Sea of
Galilee. In Ice Age, when the climate was wetter, the Sea of Galilee
was filled with brines of Lake Lisan. But in the current dry climate,
Lake Lisan shrunk and exposed a sill separating the Sea of Galilee from
Dead Sea, so the salts were flushed to Dead Sea or deposited on its
shotes and Sea of Galilee became fresh. The bottom of Mediterranean
contains several basins separated by sills. One can expect that if the
Mediterranean were to dry up, some basins would receive rivers
overflowing to other basins, and thus become freshwater lakes.

Relevant Pages

  • Re: NBC special " The Mysterious Origins of Man"
    ... observe, or change, the outcome of the experiment. ... when Glaciers broke forth with the volumes of water equal to Lake ... According to Plato's account The Atlantians were masters of the sea, ... Mediterranean Sea and the Atlantic Ocean along the Bethic and Rifan ...
    (rec.music.classical.guitar)
  • Re: Dam the Med
    ... An old man dreams of damming the Mediterranean Sea to save the world from global COOLING. ... That in turn pushes more of the very salty deep Mediterranean water out at Gibraltar into the deep ... The obstacle pushes the cold, salty water toward the surface, ...
    (sci.energy)
  • Re: Dam the Med
    ... An old man dreams of damming the Mediterranean Sea to save the world from global COOLING. ... That in turn pushes more of the very salty deep Mediterranean water out at Gibraltar into the deep ... The obstacle pushes the cold, salty water toward the surface, ...
    (sci.physics)
  • Re: DNA Studies : Humans Nearly Wiped-Out 70,000 Years Ago - And It Wasnt a Flood Either
    ... Science doesn't tell you what to believe, ... flooded the Euxine freshwater lake with sea water. ...
    (alt.politics)
  • Re: Characteristics of a really gigantic lake on an Earthlike planet
    ... As worldbuilding progressed a river ... wound up being drawn that connected the sea to the ocean. ... the area of Lake Superior, twice the area of the Mediterranean Sea. ... Personally I expect it's probably going to be fresh water; ...
    (rec.arts.sf.science)
Quantcast