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Youth Science Lessons – Energy in the Ocean Lesson 1 – Temperature & Pressure

For this month, the topic is energy in the ocean.  We will start with the term energy.  When the term is mentioned several things come to mind, but most will focus on a source of power that provides work for us – and they would be right.  Energy does provide work – in the form of motion.  We know things move.  Trees sway, waves roll in, a bird lifts off the ground and flies across the bay to another county.  All of this involves motion, and to move you need energy to do this.  Where does this energy come from?

 

Energy comes in many forms.  Chemical energy is found within the bonds holding atoms together.  Nuclear energy holds the nucleus of those atoms together.  Thermal (or heat) energy is derived from the motion of particles.  Sound (or sonic) energy is found in sound waves (or vibrations).  And there are many others.  Some energy is in a resting stage (stored) and is called potential energy.  Other forms of energy are moving from one location to another (motion) and is called kinetic energy.  And here is another interesting fact about energy – it cannot be created, nor destroyed – only transferred from one form to another. 

Photo: Molly O’Connor

Energy is something all living organisms need.  For your brain to function, to allow your arms and legs to move and your heart to beat – you need some source of energy.  We consume food – three times a day.  Food is a menagerie of chemical compounds bonded together.  We digest that food (break those bonds apart) and acquire that energy.  This energy is used to perform work we need – mentioned above.  What energy we acquire and do not use is stored – fat in animals, starches in plants.  We use thermal energy to help warm up.  Our metabolism functions best at the higher end of thermal range – about 98° for us.  Too much higher (above a fever) and our own chemical make up begins to disassociate – we could die.  If we get too cold, thermal motion begins to slow, we begin to slow, and this could also lead to death. 

 

Which brings us to the first of the energy forms in this topic – heat.  As mentioned above, thermal (heat) energy is energy released during motion.  If you look at a brick you see what we would call a solid – an object with a fixed shape and volume, no change while we are looking at it, no motion.  BUT it is moving.  At the molecular level all atoms vibrate slightly – they move.  We call this Brownian movement, and the space that the vibration occurs is fixed – sort of.  If you apply more energy, the movement increases, the space between the vibrations increases, and the heat energy released increase.  If you reduce the energy, the opposite happens.  We can measure this change in heat by measuring the temperature

Image: University of South Florida

Think about it.  You place a liquid material within a glass tube – usually mercury or alcohol.  As the thermal energy in the environment increases, the motion within the atoms of the liquid increases, the area in which those increasingly moving atoms increases and expands, the liquid is within a glass tube so it is forced upwards, we have numbers along the side of the tube and we read how high the liquid moves – the temperature. 

 

Warm thermal energy does the same in the ocean.  As the sun warms the water, the temperature increases.  Warm objects (water included) begin to expand and become less dense – they rise.  So, the ocean begins to “rise”.  The highest rate of warming occurs near the equator.  The warm riding water here begins to move away from the equator and towards the poles.  This is part of those forces that generate the ocean currents (more on this in another lesson).  Moving this warm water away from the equator moves heat from the area as well.  This dispersal of heat helps warm what would be a colder part of the world (climate) and keeps the equatorial waters from overheating.  The ocean is important in regulating the temperature and climate of the planet. 

 

As the warm currents reach the polar regions, they begin to lose their heat.  The waters cool, the molecules slow their motion and the water becomes more dense.  This dense cold water begins to sink towards the ocean floor, sliding across the planet – driven by other forces we will discuss later – before warming and rising again – the great ocean conveyor belt.  

 

While this is all going on, there are thoughts about the ocean floor.  At the surface the ocean is warmed by the sun, but as you descend that energy source is less, the waters become cooler.  At one point in the water column there is a drastic decrease in water temperature – the thermocline.  We have all probably experienced this even in shallow water.  It is nice a balmy temperature near the surface, we take a deep breath and dive down, near the bottom we pass through a layer of very cold water – the thermocline.  As you might expect this thermocline does not remain at the same depth all day.  As the sun rises, it reaches deeper into the sea causing the thermocline to descend deeper.  In the evening, the suns strength weakens, the waters cool, and the thermocline is found closer to the surface.  This layer of water – the thermocline – separates two different worlds in the ocean, and the marine organisms are well aware of where it is.  Many times, layers of small planktonic food will ride the thermoclines up and down, the plankton feeding fish will follow, as will the predatory fish. 

 

The ocean is a major player in the movement of heat and energy across the planet.  But there is something else that changes with depth… the pressure. 

 

Many of us have dove to the bottom of a swimming pool and experienced the change of pressure.  You can only imagine the pressure change at the bottom of the ocean. What is going on? Here is a brief explanation. 

The atmosphere
Photo: Molly O’Connor

A solid material, like ice, has a definite shape and volume.  As you increase the thermal energy on the solid object the molecules within increase their motion.  As their motion increases the space between the molecules increases and their density decreases.  At some point the temperature is high enough to cause the solid to change state – to liquid – this is the melting point (32°F for ice).  Liquids maintain their volume, but no longer have a definite shape.  Continue the heat and the molecules move more – density decreases – and the liquid rises (which has been discussed in this lesson and others).  At some point the liquid will change state again to gas – the boiling point (212°F) for water.  But we know water begins to evaporate at much lower temperatures.  As a gas there is no definite volume not a definite shape – the material now takes the volume and shape of the container it is in.  If there is no container – gas rises (most gases rise).  This rising gas becomes part of our atmosphere and, theoretically, should continue to rise into space.  But it does not… our atmosphere remains with us.  What is happen?

 

Answer… gravity. 

The gravity of the planet holds the gaseous atmosphere to the surface of our planet.  As a matter of fact, it is pulling towards the surface (or ground) of the planet.  Things standing on the surface (trees, elk, me and you) are in the way.  The atmosphere is pushing on us to reach the surface – applying pressure on our bodies while doing so – atmospheric pressure – air pressure. 

 

The pressure on us here at the surface is 14.7 pounds of air for every square inch of our bodies (14.7 p.s.i.).  Yet we do not collapse under this pressure.  We have a rigid skeleton, fluid body, and can adjust our internal pressure via our inner ear. 

The Rockie Mountains.

So, what happens when we get into a car and drive up into the mountains?  We move from 0 ft. at sea level to 8,000 feet in the Rockies.  There is less atmosphere above our heads in Denver CO than there is here at sea level – there is less air pressure.  As this pressure decreases while driving, we can feel it.  It sounds as if we have headphones on, harder to hear what is going on around us and – sometimes – we get a headache.  Then, miraculously, we feel the adjustment in our ears – it becomes clearer, we can hear better – the air pressure internally has been adjusted by our body.  We can do this ourselves by chewing gum or yawning. 

 

Climbing to 30,000 feet in an airplane to get to Denver is a huge change on our bodies.  There is much less air above us there and the air pressure is much less.  Technology has solved this problem by pressurizing the cabin inside the plane to 14.7 p.s.i. (sea level) so we do not feel discomfort. 

 

So, lets go the other way.  Down… Down below the ocean. 

As soon as you dive into the sea you still have the pressure of the entire atmosphere on you, but now add water – which weighs much more than air ( 62 lbs./ft.3 as compared to 0.08 lbs./ft3 for air).  The ocean to is being pulled by gravity towards the ocean floor.  Being that water weighs more than air, we feel this increase in pressure much faster.  At sea level (standing on the beach) the air pressure is 14.7 p.s.i., or as some say – 1 atmosphere.  As you descend into the ocean swimming down the pressure will double to 29.4 p.s.i. (2 atmospheres) at 33 feet (10 meters).  Every 33 feet (10 meters) you will add another 14.7 p.s.i., or another atmosphere.  So, at 100 feet you would have a hydrostatic pressure of 4 atmospheres (remember it is not 0 atmospheres at the surface, but 1 atmosphere).  4 atmospheres will be 59 pounds of pressure for each square inch of your body (54 p.s.i.) – three times as much as it is at the surface. 

 

Humans routinely dive to depths of 100 feet while using SCUBA and will endure this increase in pressure.  Divers are taught how to equalize this pressure change as you would if driving up into the mountains.  If you can “clear” (as it is called) you can descend down.  If you cannot (sometimes you have a cold or something) you cannot and must return to the boat.  Our bodies can withstand this pressure.  But how low can we go?  Many trained divers can go below 200 feet (104 p.s.i.) and some 300 feet (148 p.s.i.).  This is about it – and only those who have been trained can reach these kinds of depths. 

Descending devices.
Photo: Louisiana Sea Grant

What about the creatures in the sea?  Do they experience this change in pressure?  Yes… they do… and most have developed adaptations for dealing with it.  Many of us know that catching a snapper on rod & reel at 80 feet and reeling them in quickly decreases the pressure on their body quickly – too quickly for them to adjust.  The pressure is released quickly, and the pressure forces some their internal organs to extrude through their mouths.  They may still be alive.  We can use a hollow needle to puncture their swim bladder (a gas bladder that expands when the pressure decreases – because internally it is gas – and forces their gut out of their mouth).  With the release of pressure on the swim bladder the gut can go back into the fish and they can be released.  Science has shown that many of these fish do not survive this.  There are several different descending devices available for fishermen who must release their deep water catch due to a fishing regulation that will not allow them to keep the fish.  The important thing is to get them back to depth ASAP – this is their best chance.

 

What about deeper?

What about 1000 feet?  10,000 feet? 30,000 feet? 

Can we reach those depths?

Can marine life survive at those depths?

The quick answer is… yes.  We can reach these depths and fish do live there as well. 

For us it requires technology.  Our bodies cannot withstand these high pressures.  But we have designed vessels that can – and keep the internal pressure of the vessel at 1 atmosphere – this is known as 1 atmosphere diving.  Deep sea submersibles and submarines are examples of such ships. 

William Beebe’s bathysphere.
Photo: Britannica

One of the first to try this was oceanographer William Beebe.  Engineers had determined (through the extensive process of science) that the best shape for such as vessel would be a sphere.  The intense pressure of the deep sea would try and crush this ship and with a sphere – you have no corners, or pressure points, for the water pressure to act on. 

What material would you build this out of?  The team chose steel.  Makes since, logic deduction. 

But could a steel sphere still crack?

 

Time for science and the lab.  Time to test designs and sizes.  They finally came up with a steel sphere that was about five feet in height and the entrance was only 15” in diameter.  In the 1930s two men, William Beebe and Otis Barton, entered the sphere and were lowered to a depth of about 3000 feet.  Here the pressure on the sphere would be 91 atmospheres (1351 p.s.i.).  They called this sphere a bathysphere.  There were several problems with the bathysphere and engineering designs continued until they have the ships we use today on the seafloor.  We reached the bottom of the Marianas Trench for the first time in 1963. 

 

Are there creatures living down there?  Yes… and a subject for another lesson

Are there creatures who can dive to deep depths and return?  Yes… sperm whales do this often, another lesson for another time. 

 

ACTIVITY

It is a math one. 

We have determined the pressure at 100 feet and others above.  Let’s do some more. 

What would the pressure be at 1000 feet?

10,000 feet?

20,000 feet?

30,000 feet?

Would YOU make a deep-sea submersible dive to depths like this? 

What other factors would you have to consider in order to make such a dive?  What you need besides a protective vessel for such a trip?

How would you solve these problems? 

Kind of like going to the moon isn’t it?