(SNES) The Thermohaline Conveyor Belt - or what to do with your spare time until the next Ice Age

["Les Coleman" <les11@cox.net>]

Hi Everyone,

I've come across some material from Wood's Hole Oceanographic Institute
which is very interesting even very unsettling.  The very greatest current
in the oceans of the Earth is the so called Thermohaline Conveyor Belt.  It
starts in the North Atlantic where chilled very salty water sinks to the
bottom of the sea and moves down along the North American continent, under
the Gulf Stream down along the east coast of South America over between
Antartica and the tip of Southern Africa.  Here it devides with the northern
branch moving up in a clockwise direction through the Indian Ocean.  Heated
by the tropical Sun the water rises and becomes much less salty.  The
southern branch moves south of Austrailia, turns up through the central
Pacific making a clockwise loop past Alaska and the west coast of North
America.  Like the Indian loop, the Pacific loop is warmed, rises and
becomes much less salty.  Nearer the surface its begins to make a run across
the Pacific again, crossing its lower precursor near the Equator and then
making a nearly straight line to rejoin the Indian Ocean loop.  This single
current hugs the coast of Africa moving up past the Canary Island until it
finally closes the belt in the North Atlantic.

We are familiar with great ocean currents like the Gulf Stream, the Labrador
current and the Humboldt current.  These are actually byproducts of the much
greater TCB.  The energy source of this huge river is the heat of the Sun
and just as important the salinity of the water.  Very saline water is
heavier by a significant amount than most ocean water.  The TCB becomes
saltier by the evaporation of the warmed water, leaving the salt behind.
Unless this salty water sinks, there is no circulatory force.  The water in
the Pacific and the Indean Oceans simply becomes warmer, but it doesn't
move.  The current that we are familiar with such as the Gulf Current cease
to flow or are altered in their paths.

There is increasing evidence which suggests that interruptions of the TCB is
responsible for ice ages.  It doesn't take a great deal of temperature
change.  Cool Europe by an average of 5 degrees and glaciers will start to
move down mountains, filling high valleys and then joining other snowfields
and glaciers in a new ice cap.  That is all it takes, about 5 degrees.

All it takes to trigger an ice age is a supply of fresh water in the North
Atlantic.  The last great ice age was triggered when an ice dam in northern
Canada melted, emptying the then larger Great Lakes out the newly formed
Saint Lawrence River.  Fresh water diluted the salty cold water and it
simply stopped sinking.

The changeover from an active to a dormant conveyor is startlingly swift.
It can halt within a decade.  Terrible winters can begin almost immediately.
If it happened today, Europe could be facing Siberean like winters within
this decade.

Why is this unsettling?  Simply the fact that the largest supply of fresh
water outside the Antartic, the Greenland Ice Field is melting rapidly.
Long before we noticed any rise in the oceans, the TCB would stop.  The
first sign we would see would be a global warming.  The second would be a
decrease in North Atlantic salinity.

Speculation?  Maybe, but WHOI has noticed a sharp drop in the salinity of
the North Atlantic from fresh water leaving Greenland.  And weren't there a
bunch of folks running around in Kyoto talking about Global Warming a couple
of years ago.

In any case, it goes to show why simple minded ideas about Global Warming
may not be what we excpect.

Les Coleman
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