SPEAKER: One of the most remote places on our planet
is the deep ocean, yet the movements of water,
the currents in the dark depths, affect the water and air that
meet on the surface of the sea.
The interplay of water and air over thousands
of miles of ocean affect weather, climate, life
on Earth.
[BIRDSONG]
The motions of deep water also affect the wastes
that are dispersed in the open ocean and the whole cycle
of life, the migrations and habits
of marine creatures in the sea.
This is the story of a search for a turbulent ocean force,
call it a deep sea storm, call it
an eddy, that could dominate the ocean currents.
To try to find an eddy in a major experiment
as part of the International Decade of Ocean Exploration,
a group of oceanographers assembled a fleet
of six research vessels.
SPEAKER: Starboard 20.
SPEAKER: Starboard 20, sir.
SPEAKER: Half speed.
Half speed.
SPEAKER: Keep a sharp watch for it now.
SPEAKER: Major, let speed down.
SPEAKER: Dead slow
SPEAKER: Eddy, we're coming up with a course change.
SPEAKER: Very good, sir.
SPEAKER: Put her in the hand steering.
SPEAKER: Hand steering, sir.
SPEAKER: The ships carried a variety
of ingenious new instruments that could
measure the flow of deep water.
All the instruments were to be placed
in the same piece of ocean at the same time in search
of a storm in the sea, an eddy.
Henry Stommel has explored currents
in the Atlantic, Pacific, Indian oceans, and many other places.
He's been elected to tell this story about a group of very
different oceanographers who have measured ocean
currents all over the world, trying to find an eddy in one
piece of ocean together.
HENRY STOMMEL: We, a group of oceanographers
from a dozen or more universities in the United
States and the United Kingdom, have joined together
in an experiment that we call the Mid-Ocean Dynamics
Experiment or simply MODE.
Each of us has a different approach
to oceanography, different instruments, skills.
We're independent people anxious to protect our individuality
and freedoms.
We're not sure we like this kind of big science.
We're not used to it.
But we are faced with a number of very big problems.
How do the oceans move?
And what drives them?
We'll try to tell this story from the beginning
as it happened, but perhaps, first, we
ought to go back some time earlier.
Once, a long time ago, it was believed
that ocean currents were driven by sea monsters and gods that
had the power to drive the warm equatorial water up
to the cold Arctic or to drive the seas eastward
or westward on other long journeys of thousands of miles.
Today, we understand that the atmosphere drives the ocean
and that in turn, it receives energy back from the ocean.
We know that the surface of the North Atlantic
is driven mainly by the winds.
The slow, broad movements of large masses of water
are broken only by the strong, rapid northward flow
of the Gulf stream.
But how does the water below the surface move?
And how is it driven?
Based on temperature readings, we now
suspect that the lower layers move in an opposite direction
to the surface flow, affected mainly
by temperature differences.
This is the large picture.
What might one expect in any given small region
of the ocean?
A slow, uniform current driven by very gradual temperature
differences, so slow that it might take months or even
years to detect any motion.
But the currents in the deep ocean
had never been measured directly.
In 1959, the Aries from Woods Hole
set sail to try out a new tool for measuring
the deep currents.
John Swallow, a British oceanographer,
had aboard some new aluminum tubes
that he had designed to float in deep water at fixed depths
and to give off sound signals that
could be followed by the ship.
Swallow supposed that the Aries could easily
keep up with a cluster of six of the floats
as they supposedly inch their way along
together in the deep ocean.
But to everyone's surprise, the float
seemed to be moving neither slowly nor uniformly.
Instead, they moved at speeds 10 times faster than expected
and in random fashion.
What were the forces driving the water
in this rapid, irregular way?
The Aries soon had to abandon the unequal chase,
but fascinating questions had been raised.
Are there storms or weather systems, eddies,
in this as well as in other parts of the deep ocean?
The place we went to for guidance in our ocean research
was surprisingly the National Center for Atmospheric Research
in the mountains of Colorado.
The large computer normally used for studies
of atmospheric turbulence was put
to work to produce theoretical eddies in the ocean.
A number of meetings were held by a theoretical panel of MODE.
Allan Robinson, who was at most of these meetings,
can describe them.
ALLAN ROBINSON: We spent a number
of weeks trying to decide how ocean storms might be made
by winds, by temperature differences,
and by mountains on the sea bottom.
Similar factors can produce atmospheric storms.
And then we try to decide how these theoretical eddies might
help us to set up an experiment in which we
could get at the real eddies in the open ocean.
FRANCIS BRETHERTON: And so what is the experiment really going
to tell us?
ALLAN ROBINSON: All right.
First, there's two questions.
One is, to what extent can our study these mechanisms now
let us think more rationally about the design
of the experiment, the actual laying out of the array?
And can, when we do that, get an array
which is going to allow us to determine the local dynamics
of the eddies themselves?
Not where they come from, but the--
FRANCIS BRETHERTON: What's going on?
ALLAN ROBINSON: --forces which--
FRANCIS BRETHERTON: In other words, what's there?
ALLAN ROBINSON: --what's going on right there?
And how they're hanging together.
FRANCIS BRETHERTON: All right.
Right now.
ALLAN ROBINSON: Yeah.
SPEAKER: The atmosphere is very helpful
because we think that the basic forces in the atmosphere
are really rather similar to those in the ocean.
HENRY STOMMEL: Between the southeastern coast
of the United States and the island of Bermuda,
a piece of test ocean, less than 400 miles in diameter,
was finally selected.
It's a small piece of ocean compared
to the size of the Atlantic, but a large enough area
to contain a few eddies.
[MUSIC PLAYING]
In the spring of 1973, after four years
of talking, planning, testing, arguing, and worrying,
we put out to sea to try to find something that no one had ever
found before, a deep sea storm.
After three days steaming, we reached MODE waters,
which looked no different from the rest of the Atlantic Ocean.
My approach to oceanography is to try to ask the simplest
possible questions.
And one of the oldest and simplest ways to ask questions
about the sea is to take water samples and find out how warm
and how salty the ocean is at different depths or layers.
We'll be collecting water samples
on all of our six ships.
We are not trying to catch an eddy in a bottle.
If there are eddies around, they're
much too big to fit into a bottle.
What we are trying to do is to get a three-dimensional picture
of the temperature and salinity layers in the MODE area
to map out the lines of equal density along which
the water ought to flow.
If water sampling represents the traditional approach
to ocean currents, then current meters
and other direct measurements of flow represent the new.
Bob Heinmiller, aboard the Chain,
can describe the complex job of placing current meters up
and down and around the MODE area.
BOB HEINMILLER: The first thing we have to put out
is the surface mooring.
It marks the center of the MODE area,
carries a wind recorder, some navigation radio beacons,
and a flashing light.
The central mooring will sit on the surface,
the only gear that will be visible in the whole MODE area.
Everything else will be hidden below the surface.
The passing ships are certainly going
to wonder what this strange-looking object is out
in the middle of the ocean, but they'll stay away from it,
we hope.
The main instruments on the moorings
are the current meters.
The cylindrical case contains all the electronics.
At the bottom is the rotor that measures the flow of the water
past the instrument.
The records of speed and direction
are stored inside the meter case on magnetic tape.
The current meters are brought back to the surface
by these hollow glass balls, each of which
can lift up to 60 pounds in water.
The balls are encased in plastic casings which we call hardhats.
They're bolted together, and they're
attached to sections of chain.
The whole mooring, topped by a radio beacon and a light,
is first laid out on the surface.
Since the top of the moorings will
be about a quarter of a mile below the surface,
we have to pay out almost three miles
of glass balls, current meters, and cable for each mooring.
We developed a technique over the years.
After the top of the mooring is over the stern,
we steam away from it, slowly going upwind.
When the mooring is completely strung out,
we try to end up directly over the position on the ocean floor
that we want the anchor to rest.
The trick in all this is timing the operation.
Obviously, there are a lot of things that can go wrong.
If you work too fast or the ship goes too slowly because
of the wind, you can suddenly find yourself
with a ton and a half of anchor on your hands ready to go
and you're simply in the wrong place.
Sometimes we simply have to hang on to the anchor for an hour
or so, dragging this three miles of paraphernalia
behind the ship, trying to get into the right position
and constantly worrying about passing ships, sharks biting
the line, or what have you.
We've had a few close calls.
I'm always a little tense during mooring launch.
There are just too many things that can go wrong.
It's always a great relief to finally get rid of the anchor
and watch it drag the mooring string down into the water.
You sometimes wonder whether you'll ever see
any of that equipment again.
It's a little unnerving in a way.
It's difficult to describe just what happens below the surface.
We'd have to start with this familiar sketch of the MODE
area.
And then we would have to stretch it
in the direction of the depth, way out of proportion
to its actual shape in the MODE area
in order to see the central mooring
in place and the first instrument mooring
and the first subsurface mooring falling
to the bottom, pulled down by the weight of the anchor.
Well, ship time is a very valuable commodity.
And so we work straight through day and night.
We have two separate crews that alternate putting out
the current meters through the MODE area on these 17 moorings.
DOUG WEBB: We are launching a set of floats
called SOFAR floats.
These are brand new, handmade instruments
that are being used for the first time in MODE.
My name is Doug Webb, and I am an engineer, an ocean engineer,
if you like.
This kind of engineering involves building
a capsule that can withstand the rigors of the deep ocean
and also an acoustic system that can transform
a small amount of energy into an underwater sound that can
be heard 1,000 miles or more.
We will have launched 20 SOFAR floats in the MODE area.
They have no connection to the ship, to the surface,
or to the bottom of the ocean and are
entirely free to be carried along by the deep currents.
To the extent the ocean is variable,
each float will follow a separate course.
Ready to launch in air, the float weighs about half a ton,
but on the surface of the water, it weighs only 6 pounds.
It settles slowly, very slowly, weighing less and less
as it goes down until about a mile below the surface,
it weighs nothing at all and is neutrally buoyant,
just like a constant altitude balloon floating in air.
The floats take about 1 and 1/2 hours
to reach their depth of 5,000 feet.
Each float transmits its own slightly different sound
pattern, which lasts for about 2 seconds every minute
of the day for the next 4 months.
The signals from the floats sound
like a short blast of a foghorn.
We call it a pong to distinguish it
from the ping made by the floats used by John Swallow.
The pongs can be monitored aboard ship
to see if all is well, but the floats
are not tracked from the ship.
We operate four shore-based listening stations
to find out exactly where the floats are
traveling in their journey with the ocean currents.
The floats measure the same motions as the current meters,
but in a different way.
The float stays with a body of water
while a current meter measures the flow past one point.
The current meter might see an underwater storm
from a fixed point as a slowly evolving passing
event, while the float caught up in the storm
and carried inside it for months could see the storm in quite
a different way.
JAMES BAKER: Our instruments are like barometers,
which sit on the floor of the ocean
to measure the shifting weight or pressure of the ocean above.
We hope that we can use the highs and lows of ocean
pressure to make maps in the same way
that weathermen use the highs and lows
of atmospheric pressure to describe weather systems
and currents.
But we need greater accuracy.
We have to measure the addition or subtraction
of only 1 or 2 inches of water at a depth of over 4 miles.
Each of the components has to be protected
in a heavy casing in order to withstand
the pressure of more than 8,000 pounds per square inch.
We have to learn about the technology at the same time
we learn about the ocean currents.
With instruments on moorings, others
floating through the middle of the MODE area
and still others sitting on the bottom,
it would appear that we have covered the full range
of possibilities.
But we also have instruments that go from top
to bottom called profiles.
Tom Sanford's profiler measures currents continuously
in the whole water column.
An advantage of profiling is that unlike some
of the other experiments, the results
are immediately available.
It is possible to look at the numbers right away
and then change the experiment as you go.
FRANCIS BRETHERTON: I haven't brought any instruments to sea.
I'm a theoretician, and this is my first oceanographic cruise
of any kind.
I was somewhat seasick the first few days,
even though the weather was good.
My job at sea is to stand one of the three watches
making hydrocasts or water catching,
as Henry might call it.
I begun to feel like a bona fide seagoing oceanographer,
even though I might not look like one.
As far as my theoretical work is concerned, what I can do at sea
is to get a first look at some of the data
that we're gathering.
HENRY STOMMEL: With all the trials and a huge effort
by hundreds of people, we put out
a full array of all the instruments
that can measure deep ocean currents.
Related experiments going on in the same piece of ocean
at the same time.
And now that we have laid them all out
and 4 months have gone by, we've got
to try to get them all back again.
Sound signals from the ships to the instruments
tell them to drop anchor and come back home.
SPEAKER: It looks about right for letting her go, George.
SPEAKER: Right.
Anytime.
SPEAKER: OK.
Release command one.
OK, here she goes.
SPEAKER: Yeah, 1 kilometer exactly.
326.
726.
SPEAKER: She's released.
SPEAKER: Bridge.
SPEAKER: Yeah, releases as far as she's on the way up.
We should get the radio in about 3 or 4 minutes.
Roger.
Bridge of 400 meters dead ahead.
SPEAKER: OK, we have it visually.
SPEAKER: Watch out.
SPEAKER: Takes about 5 minutes for the first glass balls,
the ones that are at the very top of the mooring
to hit the surface.
With the lower end, takes about an hour for the entire mooring,
all the wire, the glass balls, the instruments
to reach the surface, a whole hour to come 3 miles straight
up through the water.
As the instruments come aboard, one
of the first things we look for is
to find out whether they're still working and relatively
intact.
If they have any bubbles, little Jets of water
coming from inside the case, or if they're
a lot heavier than usual, we know right then we've
got a problem.
A few meters were flooded by small leaks in their cases.
At the huge pressures in the deep ocean,
even a tiny leak can be disastrous.
Seawater is very corrosive, of course,
and just destroys the electronics.
Inside of the meter just gets eaten up very quickly.
We can usually save a few spare parts
if we hose them down with fresh water
immediately after we open them up.
That's kind of an agonizing process.
You've got $8,000 worth of electronics,
and here you are running a garden hose on it,
but it's the only way maybe to save part of it.
We were pretty lucky this time.
Almost all of the meters came back intact.
HENRY STOMMEL: The floats have small ballast weights
that are also released on command by sound signals
from the ship.
We bring the ship close to the estimated float position
and then start searching.
The problem now is to see the tip of a 12 inch tube
in the open ocean.
SPEAKER: Oi!
Port bow!
SPEAKER: We depend entirely on the considerable skill
of the ship's personnel to sight the float,
to bring the ship alongside, to attach a line to it,
and to bring it aboard.
Is very easy to get caught up with this technology
and engineering, but our real purpose
is to improve our understanding of deep ocean circulation.
SPEAKER: The anchor on Baker's bottom instrument
is the tripod itself.
Again, a sound signal sets off a charge
and releases the instrument.
We tend to worry a bit while the instruments are out.
So it's a real joy to spot them when they reach the surface.
The main point is that we're very
interested to know what they have
recorded while sitting down there in that quiet darkness.
SPEAKER: One part of the search is over.
The measurements have been made and recovered.
Now another part of the search begins.
The measurements for the most part
have been stored on magnetic tape inside the instruments.
The tapes are fed into computers,
and the information is worked up into a number of forms, charts,
maps, graphs, computer images.
When all the data has been summarized,
the scientists can synthesize the results
into a meaningful statement of conclusions.
A meeting was held in November, almost a year
after the meeting in Bermuda, at which we compared and presented
our results.
THOMAS SANFORD: We made about 70 profiles.
DENNIS MOORE: About 800 density stations
during the course of the experiment.
WILLIAM SCHMITZ: Our principal success to date
is that we have definitely found what we were looking for,
a MODE eddy.
ALLAN ROBINSON: It's really there.
We did catch one.
DONALD HANSEN: Which by--
well, that's good fortune, I guess.
Appears to have been reasonably well-centered
within the experimental array area.
SPEAKER: What we were able to see for the first time was
a deep ocean storm, a developing weather system
with changing temperature, pressure, and currents.
The dark highs and lows are the eddies
with the water swirling around them.
Fortunately, a high pressure area
developed in the center, a central eddy,
which revealed some of the main features, a changing
shape roughly 80 miles in diameter with speeds
at a 100 times faster and stronger than the mean
circulation of the deep Atlantic Ocean.
Compared to an atmospheric storm, it may be slow,
but it has the massive weight of the water behind it, which
gives it more energy than a thunderstorm,
and it lasts 1,000 times longer.
These eddies must be all over the ocean,
the weather of the deep sea.
SPEAKER: We now have a brief view of the currents
and the storms in one small region of the ocean.
What we'd like to know is how the whole ocean moves
and behaves the way it does so that we can couple
the circulation of the ocean to that of the atmosphere
to understand the changes in weather and climate
they jointly produce.
[MUSIC PLAYING]
FRANCIS BRETHERTON: But I think that we
found something else, a way to work together without giving up
our individual freedom to do what we want
to do in our own way, each contributing
his individual skills to a common goal.
SPEAKER: We placed a number of different instruments
in the same piece of ocean at the same time.
And the results taken together seemed
to be much greater than what each of us
might have done in his own piece of ocean in his own time.