Unit 6 Physics of the Ocean

1. Unit 6 Physics of the Ocean

2. Pressure • Scientists measure pressure in units called bars. • At sea level, the weight of the atmosphere exerts a pressure of about one bar. • Underwater, pressure increases by one bar for every 33 foot (10 meters) increase in depth

3. What causes the extra pressure? • This pressure is caused from the weight of the water. • This means that at 230 feet, the total pressure is 8 bars, or 8 atmospheres (eight times the surface pressure). • This pressure increase poses a serious challenge to human exploration of the oceans. In fact, the deep parts of the oceans are relatively unexplored, as compared to the rest of the planet.

4. What can divers do? • Divers going into the ocean have to breathe pressurized air or other gas mixtures. • This can cause problems in itself, however, because of excess gas in the body tissues. • This limits the depths that humans are capable of diving to.

5. As divers make their way back to the surface, they sometimes must make timed stops to release excess gas. • If they arise too quickly, a condition called “bends” can occur. • After working underwater for hours at a time, professional divers undergo routine controlled decompressions in a special pressure chamber. These chambers are also used to treat pressure-related diving illnesses, including “bends”.

6. What is the “Bends”? • Joint Pain (The Bends) – ranging from mild tingles to excruciating pain, usually in the large joints such as the knees, elbows, ankles, shoulders and neck. This is why they call it the bends – it makes the diver hobble and makes his body look bent. • Skin Bends – Itchy rash, feeling of crawling insects, swelling and mottling of the skin. Usually affects the upper torso and neck area. • Brain– confusion, amnesia, dizziness, black outs, headache, vision problems, fatigue or strange behavior. • Spine/Nervous System– Strange sensations, paralysis, chest pain, incontinence, numbness and muscle weakness/twitching. • Inner Ear (“The Staggers”) - Hearing loss, extreme vertigo and loss of balance. • Lungs (“The Chokes”) – Deep burning chest pain, shortness of breath, pain when breathing and a dry cough. The Rash of "Skin Bends"... Belly Button Piercing Not Included!

7. Buoyancy • How does a boat or ship carrying hundreds of pounds worth of stuff float while that same stuff would sink to the bottom of the ocean if dumped overboard? • How come when you're in a pool and you stretch your body out flat you float. But, if you wrap your arms around your legs and curl up into a ball you sink? • It all has to do with how much water is pushing against you and a scientific principle called buoyancy.

8. When you stretch out flat more water pushes against you since your body is laid out flatter. When you curl up into a ball, less water is pushing against you, so you sink. •  If the total area of the object that makes contact with the water is large enough, the object floats. The object must make room for its own volume by pushing aside, or displacing, an equivalent (or equal) volume of liquid.

9. Archimedes Principle of Buoyancy A floating object displaces a volume of fluid equal in mass to the floating object empty loaded with fish Displaced water

10. When you place a block of wood in a pail of water, the block displaces some of the water, and the water level goes up. • If you could weigh the water that the wood displaces, you would find that its weight equals the weight of the wood.

11. This doesn't mean that if you had a few blocks of wood that were exactly the same size and shape, they would each displace the same amount of water. • A block of wood made of oak, for example, sits deeper in the water (thus displaces more water) than does a block of pine. The reason is that it's heavier for its size, or denser—in this case, the molecules that make up the oak are more closely packed together than the molecules that make up the pine.

12. If you could somehow keep increasing the density of the block, it would sink lower and lower into the water. • When its density increased enough to displace an amount of water whose weight was equal to the weight of the block, it would, in a sense, become weightless in the water.Making the block just slightly denser would cause it to sink to the bottom.

13. Objects that are less dense than water will float. • Objects that are more dense than water will sink. • Objects that are the same density as water will neither sink nor float. float Neutrally buoyant sink

14. Buoyancy Adaptation • Blubber • Swim bladder • Fatty liver • Buoyancy Compensator Device (BCD)

15. NOVA Buoyancy Activity

16. Properties of Light in the Ocean

17. Light & Sound • Light and sound behave very differently in water than in air. • Most light wavelengths are quickly absorbed by water, a fact that both explains why the sea is blue and why ocean life is concentrated near its surface. Almost the entire marine food chain relies on light energy driving plant growth. • Sound, in contrast, travels better in water, a fact exploited by animals such as dolphins.

18. Light in the Ocean • White light, such as sunlight, contains a mixture of light wavelengths, ranging from long (red) to short (violet). • Ocean water strongly absorbs red, orange, and yellow light, so only some blue and a little green and violet light reach beyond a depth of about 130 ft (40m).

19. Light in the Ocean • At 300 ft (90m), most of even the blue light (the most penetrating) has been absorbed, while below 650 ft (200 m), the only light comes from bioluminescent organisms, which produce their own light

21. Light in the Ocean • Water not only changes the color of sunlight, it dramatically changes its intensity. In clear ocean water, visible light decreases approximately 10-fold for every 75 m (250 ft) that you descend. • This means that at 75 m (250 ft) the light is 10% as bright as it was at the surface; and at just twice that depth, 150 m (500 ft), it is another 10-fold dimmer, or 1% of surface light

22. Light in the Ocean • Below this depth there is insufficient light for photosynthesis, but there is still plenty of light for seeing. This is because eyes are useful over an astonishing range of intensities.

23. Light in the Ocean • Because they rely on light to photosynthesize, phytoplankton are restricted to the upper layers of the ocean, and this in turn affects the distribution of other marine organisms. • Surprisingly, many bright red animals live at depths that are devoid of red light: their color provides camouflage, since they appear black.

25. You can demonstrate this for yourself. Cover a flashlight with a blue filter and use it to look at a red object in a dark room. Against a black background the red object will seem to disappear. It is important to remember this fact when you see pictures of bright red animals in the deep ocean. We can see they are red, because we use bright white lights on the submersible to illuminate them. But in the dim blue light, which is their natural environment, they will appear gray or black.

27. Light in the Ocean • This squid produces a pattern of glowing spots (photophores). When viewed by a predator swimming below, the spots help camouflage its outline against the moonlit waters above.

28. Light in the Ocean • Fish have excellent vision, which helps them find food and avoid predators. Many can see in color. The lens of a fish’s eye is almost spherical and made of a material with a high refractive index. It can be moved backward and forward to focus light on the retina.

29. Sea Colors • Seawater has no intrinsic color- a glass of sea water is transparent. But on a clear, sunny day, the sea usually looks blue or turquoise. • In part, this is due to the sea surface reflecting the sky, but the main reason is that most of the light coming off the surface has already penetrated it and been reflected back by particles in the water or by the sea bed.

30. Sea Colors • During its journey through the water, most of the light is absorbed, except for sonic blue and green light, which are the colors seen. • Other factors can modify the sea’s color.

31. Sea Colors • In windy weather, the surface becomes flecked with white, caused by trapped bubbles of air, which reflect most of the light that hits them • Rain interferes with seawater’s light- transmitting properties, so rainy, overcast weather generally produces dark, gray-green seas

32. Sea Colors • Occasionally, living organisms, such as “blooms” of plankton, can turn patches of the sea vivid colors. Ocean Shades- A green sea is sometimes caused by the presence of algae. Turquoise is the usual shade in clear tropical waters, while gray water flecked with white foam is typical of windy, overcast days.

33. Underwater Sounds • The oceans are noisier than might be imagined. • Sources of sound include ships, submarines, earthquakes, underwater landslides, and the sounds of icebergs braking off glaciers and ice shelves

34. Underwater Sounds • In addition, by transmitting sound waves or bouncing them off underwater objects (echolocation) whales and dolphins use sounds for navigation, hunting, and communications. • http://www.dosits.org/audio/interactive/#/50

35. Underwater Sounds • Sound waves travel faster and father underwater than they do in air. • Their speed underwater is about 5,000 ft per second (1,500 m/s) and is increased by a rise in the pressure (depth) of the water and decreased by a drop in temperature.

36. Underwater Sounds • Combining these two effects, in most ocean regions, there is a layer of minimum sound velocity at a depth of about 3.300 ft (1,000 m). This layer is called the SOFAR (Sound Fixing and Ranging) channel. • The properties of the SOFAR channel are exploited/used by people using underwater listening devices and, it has been theorized, by animals such as whales and dolphins.

37. Underwater Sounds • The Austrian-American scientist Walter Munk (b. 1917) pioneered the use of sound waves in oceanography. • A professor at the Scripps Institute of Oceanography in San Diego, California • Munk demonstrated that by studying the patterns and speed of sound propagation underwater, information can be obtained about the large-scale structure of ocean basins.

38. Underwater Sounds • The peaks and troughs in this spectrogram show the changes in frequency of a few seconds of repeated sound made by a humpback whale.

39. How does SOund Fixing And Ranging (SOFAR) work? • This "channeling" of sound occurs because of the properties of sound and the temperature and pressure differences at different depths in the ocean. • The ocean is divided into horizontal layers in which the speed of sound is greatly influenced by temperature in the upper layers and by pressure in the deeper layers.

40. How does SOund Fixing And Ranging (SOFAR) work? • As temperature decreases, the speed of sound decreases, and as pressure (depth) increases, the speed of sound increases. Sound waves bend, or refract, towards the area of minimum sound speed.

41. How does SOund Fixing And Ranging (SOFAR) work? Therefore, a sound wave traveling through a thermocline (a region of rapid change in temperature with depth) tends to bend downward as the speed of sound decreases with decreasing water temperature, but then is refracted back upward as the speed of sound increases with increasing depth and pressure.

42. How does SOund Fixing And Ranging (SOFAR) work? • This up-down-up-down bending of low-frequency sound waves allows the sound to travel many thousands of meters without the signal losing significant energy.