The course for a round the world regatta leads the boats through the Mediterranean Sea and the Atlantic, Southern Indian and South Pacific Oceans. On their voyage, the skippers come across a large variety of oceanographic situations: strong currents, floating ice, wave formations of every kind and biological diversity. In this course the student will learn about the foundations of the science of oceanography. You'll learn about the classification and formation of the ocean floor, how current sea satellite analysis systems work, the chemistry of the oceans and the processes that led to its formation. To follow this course does not require previous knowledge of oceanography.
2.3.2 Video Deep and intermediate water formation
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En provenance du cours de Universitat de Barcelona
Oceanography: a key to better understand our world
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2. The Global Ocean
This module will enter fully into the Global Ocean, will review and generalize the aspects previously referred to in the previous module. We will see the role of the ocean on a global scale, and how we can affect those who live closer or farther from the coast. Try to understand why it is still quite unknown and will glance nose in the marine environment. That is, how it behaves for those living beings, most who live within the ocean or in direct contact with him.
Rencontrer les enseignants
Jordi SerraDr.
Grupo de Geociencias Marinas
[MUSIC]
Let's talk about deep water formation.
Or formation of more dense waters that go towards deep zones.
Let's say that, rather, what we are doing is
to study the formation of dense waters that go towards deep zones.
They can be very deep or not so deep.
The scheme, in principle.
This we saw in another chapter, in the case of the Mediterranean.
Here we will see a little in general.
And there are two mechanisms or two situations in which it occurs.
One of them is by convection, in the broad sense, deep,
where water increases its surface density.
By evaporation in general.
Through, above all, loss of water and latent heat.
And it sinks, more or less violently, to the bottom.
Or up to a certain level.
It can be up to a restricted level,
because the bottom is still dense water.
Then we are talking about intermediate water formation.
Here, these blue lines represent isopycnals or curves of equal density.
What we have is that, when this situation occurs, normally
these isopycnals that tend to be quite horizontal.
Because in general the aquatic environment,
being the water not compressible or very uncompressible.
It tends to be stratified and therefore to have very orderly density.
Waters less dense above and as you go down, denser waters.
Whereupon the isopycnals remain horizontal.
What we see here is that this horizontal structure
is cut at a certain point and forms what is normally called a chimney.
This, I insist, we saw in the Mediterranean
and in the specific case of the formation of deep waters in the Gulf of Leon.
And here is another possibility, it is in the platform area.
This is a platform and a platform zone.
Also because there is less water.
It can be much more efficient cooling mechanism especially at times.
It is even cooling along with latent heat loss.
And then a very dense or fairly dense layer of water is actually formed in the
platform background.
It collapses along the slope like a river that collects water.
And it really behaves exactly the same as a river on land would behave.
Because we are talking about a much denser or rather dense mass of water
than the one that envelops it.
That here too can happen that there comes a time when the environmental density
is up to the one that is there.
And with that, it will spread on this point, or it may reach the bottom.
This will be called Deep Sea Deepwater Formation.
And this is cascade deep water formation.
Here we have the two schemes of the situation in the Gulf of Leon.
This is the typical area
of deep water formation in the Gulf of Leon when there are a few episodes.
And this area that is outside of what is the continental shelf.
And the vertical section, this section from A to B, we have it here.
And we also see this isopic structure in
form of chimney that commented to you.
Here the sea is seen in different points of formation of deep water that is entering
by the Gulf of Leon,
we have the Adriatic, we have the area of the Sea of Crete,
which are the main points of formation of deeper waters.
Then they are here, in the east of Rhodes
there is intermediate water formation and the area is here
there is also intermediate water formation in the western Mediterranean.
Curiously, that is a chlorophyll map,
it is seen in the area, when deep water formation is active in open sea
that chlorophyll on surfaces disappears and the water there is very transparent.
It is an indicator, it looks very clear.
Here you can see the very productive area in the Gulf of Leon.
Here too.
And here we have the absurdly blue zone
violet because there is practically no formation.
But let's go now to the ocean.
In the ocean we have
formation of deep water or dense water,
I think it's more serious to talk about dense water,
for offshore training and training
of dense waters in platform that give rise to the cascading.
The red dots are areas of dense water formation in cascading.
And, note that in general they are cold areas,
but there are some exceptional cases.
As for example here, in Mauritania,
or here in the Sea of Cortez in California, which are very warm areas.
What happens in these areas?
They are very shallow areas
practically salinas communicated with the sea.
So what is produced is a very intense evaporation,
they are areas of the desert in general, there is little rain.
Then there is a cascade but water
that instead of being cold water, it is very salty water and evidently falls.
But it is not the general thing.
Stars indicate points where there is convection in the open sea.
These are the most important points of the North Atlantic,
where virtually all the deep water of the ocean is formed.
In these two points, in these two towers north of Iceland and
between Baffin and Greenland.
There are some spots here of deep water formation in open sea on the coast
Antarctica, in the area of the Indian Ocean, Pacific.
And then some zones of cascading of different levels.
These are usually waters that generally produce intermediate waters.
In general we have intermediate water formation.
This is indicating the Mediterranean.
In the Mediterranean they are deep waters within the Mediterranean basin,
the same as in the Red Sea.
It produces deep water within the Red Sea basin
then when they leave for Bab el-Mandeb and they are occupying.
In the Arabian Sea they are located at a certain depth
above what the background is.
And the same thing happens in Mediterranean when water leaves for Gibraltar.
Pre-conditioning.
What does pre-conditioning mean?
Means the conditions to which the surface water has to reach
so that with a relatively small disturbance.
That is, with a cooling,
with a loss of heat or a relatively small increase in salinity.
There is a jump that causes the water to go to the bottom.
So what does it mean?
The greater the density that we have in surface in the winter season.
That is the time in which the formation of depth is usually given,
I said before.
Except in some very specific and specific cases that have their interest.
But they have no value from the point of view of the amount of water they produce.
For what we have here, we have red values that correspond
to areas where in winter maximum densities are reached.
Note that they are, in general, areas of the North Atlantic.
We obviously have the entire Antarctic circumpolar zone.
Some points near Siberia in the Pacific,
but really much smaller in the Pacific.
And, instead, we see it here, despite being in the Arctic.
We have that density is low, just as it is in equatorial areas.
This would make sense from a thermal point of view.
And the same happens in the equatorial zones also in the Atlantic.
And here it gives us a little clue as to what is the origin, in fact, of this.
It is not only a question of temperature, but also a matter of salinity.
That is, we are talking about important contributions of fresh water on the surface.
What they do is that the surface is as with a cover
which prevents the attack, say,
or it makes the attack of the wind or the
cooling is inefficient from the point of view,
or that the increase of density that provokes is minimum
and not reach the levels that would correspond.
The typical case in the Baltic Sea, is also a sea that
also has very low salinity levels.
That is the situation.
Where are they most likely to form?
Naturally in the North Atlantic area and in the Antarctic Circumpolar zone,
and in some little places.
And, of course, in the natural seas such as the Mediterranean,
the Red Sea, including the Persian Gulf.
Then the waters that are formed.
Levels are formed
I told you before that water forms that can reach the bottom or waters that
they arrive simply at intermediate levels.
This would be the intermediate water map.
In general we have intermediate waters that form in the Mediterranean
and we have them here, are placed again about 1,000 meters in the Atlantic.
And those that are formed in the Red Sea we have them here.
We have intermediate waters that form in other areas of the ocean.
That they are occupying here.
In general they are waters that form in the Antarctic zone.
These intermediate waters here are formed in the Labrador area and these are not.
These are from the North Pacific.
They are formed in the North Pacific, it has a relatively limited scope.
And these are intermediate waters of the Indian that are formed locally.
He has no more.
And finally we have deep water, deep water
Antarctica filling, deepest background.
And the deep water that forms in the Arctic that is this from here.
This water from here that reaches the bottom is the one that then circulates,
and this is more relegated, to more depth.
Here is a classic outline of how deep water forms,
how deep water is formed from pre-conditioning.
That is, when density levels are high on surface.
Then there is, usually due to wind and cooling.
We have intense evaporation, causes a cooling and a loss
of water that immediately makes this water much denser and it sinks.
And after this comes another stage where this water is distributed and that closes
leaving the situation as it was at the beginning.
Here is an outline of how it works, far above,
the area of deep water formation in the North Atlantic.
And we see the stream to the gulf that enters the sea here,
between Iceland and Ireland, and to the Barents Sea.
Here we have a whole circuit.
This circuit that keeps the water here,
until it is only cooling the western part of this area here.
And this cooling, the winds that can come coming
Greenland and the cold zone.
And a very important, bigger glacier.
What is above the continent except Antarctica.
And then we have a deep water formation here.
And the same thing happens in this part of here.
We have the same thing here too.
In this situation here we have a circuit and how it is forming.
And here, in the T / S diagram, what we see is how they move from one place to another.
In the North Atlantic enters the water
in these conditions, is the water enters at about eight degrees of temperature
35.2 of salinity.
And, after the process, we will be below 35.
And to a degree, only, of temperature.
And in the east turn of the south,
we also have water which enters 35.1 and 7 degrees.
A little colder than that.
And how it moves to salinities that are at 34.8 and 3 degrees.
In this case the temperature has not diminished so much.
It is how you pass from one end to the other via this way through it.
And now let's tell you a bit about the main bodies of water
that are in the different oceans.
And how they are distributed in the T / S diagrams.
Here we have, essentially, the central waters formed by mixtures.
In the central areas of the oceans,
and the rest are waters formed at certain points,
as is the case of the Mediterranean that enters this point from here in the Atlantic.
And here the same for the North Pacific and South Pacific,
we have the different waters as they form here.
And to finish this part, what we are going to do is to explain a little
the tour of the "Barcelona World Race" of 2010-2011.
And what were the masses of water he found in
the T / S diagrams he found along his route.
Here the color scale corresponds to time, that is,
to day between departure day zero and day 60 that the boat arrived in Wellington.
For making a technical scale.
The "Fòrum Maritim Català", and then, from day 60 to day 114,
which was the day they arrived in Barcelona back.
And we see how the mass of water evolved.
You study waters of the Mediterranean.
Then they pass the Strait of Gibraltar and reach the central zone,
we are in the equatorial zone.
Then there is the central zone of the Southern Hemisphere.
Then they pass to the Indian Ocean and finally to the Pacific, in the Strait of Cook.
Here we are in the Cook Strait, leaving here.
Then they go south towards Cape Horn,
That is a glacier zone
and here a freshwater entry of glaciers of
the Patagonia that were merging.
One has to think that this happened just at the end of summer, early fall.
Then it returns to the central zone of the South Atlantic, equatorial zone.
The North Atlantic and back to the Mediterranean,
Note that when arriving at the Mediterranean with a temperature
slightly higher, and salinity a little lower than when they left.
Here you can see, the fronts, the route that they made in the South Ocean.
They were almost always
North side of the subtropical front, except in this section here.
I spent a day to the south, here in the South Pacific before reaching Hornos.
Only the southern tropical front is left here,
then here is the glacier zone and then back north again.
Here we have this, is the temperature, density and salinity
and those patterns.
And then you here, an evolution of temperature.
And the corresponding T / S diagram, which you've seen before, how it goes
and in this section of the same thing
and the Indian Ocean area.
The different masses that are in the position
of the subtropical front in the TS diagram.
And how they found the different waters, and finally in the Pacific.
You can see that entrance in the Cape Horn
and here we can see the subantarctic front that, practically,
they touched the eastern point of the Cape Horn area.
And with this we are done.
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