Light and Sound

1. Light and Sound Aquatic Science 2011 K. Schneider

2. Classification by Light • Photo means light • Two ways to classify by light: • Photic zone • Aphotic Zone Continental shelf: part of continent that extends under water to the shelf break Continental slope: continental shelf break to open ocean bottom Continental rise: wedge of sediment between continental slope and abyssal plain

3. Classification by Light • Photic zone – Sunlight top layer of ocean. Two divisions: 1. Euphotic zone 2. Disphotic zone

5. Euphotic Zone • Upper layer of photic zone [Surface to approx.100m (330 ft)] • Actual depth of euphotic zone may vary by location • Depth of euphotic zone is dependent on: • water clarity • productivity • Layer with most biological productivity • Plants, photosynthesis, oxygen, food

6. Disphotic Zone • Disphotic zone (dis = opposite; photic =light) • 2nd layer of photic zone; Twilight zone • Little light, not visible to humans and not enough to power photosynthesis • Some organisms you might find here: lantern fish, rattalk fish, hatchet fish, viperfish, and mid-water jellyfish • Colors: Many organisms are red-colored because red is not reflected well in this zone and thus, looks black • Red organisms are better protected from predators

8. Classification by Light • Aphotic zone = “not light” = dark zone • Extends from photic zone to sea floor • No photosynthesis (cannot occur without light) • Little food (marine snow) • Colder • More pressure than photic zone

9. Classification by Temperature • Eurythermal: upper layer of water where temperature changes with the seasons • “eury” means “wide” or “broad” • “thermal” refers to temperature • So “wide range of temperature” • Thermocline: temperature decreases rapidly with depth • Below eurythermal zone • Disthermal: zone of stable temperature • Below thermocline zone

10. Freezing Temperature • Density is mass per volume • Pure water is at its most dense (1.0 g/cm3) at 4ºC • Freezing temperature of water is dependent on salt concentration • Salt in the water, requires a lower temperature to freeze

11. Warm-up • Describe the photic zone and it’s 2 subdivisions (zones). • What color acts best as camouflage in the Twilight Zone. Why?

12. Sound http://video.pbs.org/video/1777525840 • What term describes the transmission of sounds by the dolphins? • How does it work? factsofworld.com

13. Sound • Form of energy transmitted by rapid pressure changes in an elastic medium • Sound energy decreases as it travels through seawater due to: • Spreading • Scattering • Absorption

14. Decreasing of Sound Energy • Spreading • Loss of energy as sound travels away from the source • Scattering • Occurs as sound bounces off bubbles, suspended particles, organisms, the surface, the bottom, or other objects • Absorption • Eventually absorbed and converted by molecules into very small amount of heat

15. Speed of Sound • Higher frequencies are absorbed sooner • Frequency – Determines pitch of sound • Sound waves travel for much greater distances through water than light waves can before being absorbed. • Because of this, many marine animals use sound instead of light to “see” in the ocean

16. Speed of Sound • In seawater of 35% salinity the speed of sound is about 1500 meters per second (3,345 miles per hour) • Speed of sound increases as temperature and pressure increases • Faster in warmer surface water

17. SOFAR • SOund Fixing And Ranging • Sound waves bend toward layers of lower sound velocity and tend to stay in that zone. • Loud noises made at this depth can be heard for thousands of miles

18. SONAR • SOund Navigation And Ranging • 2 Types of SONAR • Active • Passive

19. SONAR ACTIVE • Projection and return through water of short pulses (“pings”) • Example: Side-scan SONAR PASSIVE • First human use was passive • Listening-only device • Benefit of surprise because a listener can hear the loud “ping” generated by active sonar before an operator can hear the echo

20. Shadow Zone • A region into which very little sound energy penetrates • Created when sound waves arrive at the high-velocity layer, split and refract to the surface or bend into the depth. • An object beyond that area where it splits may not be detected

21. Echolocation • When sound created by an animal is reflected after it strikes an object, it creates an echo. • They locate objects by listening for the reflected echo. • The animal can tell how far away the object is by measuring the time it takes for the echo to return to them. 

22. Echolocation – Whales and Dolphins • Used for hunting, navigation, and communication • Whale songs • Generally low frequency • Provides information about the seafloor, the shorelines, underwater obstacles, water depth, and the presence of other animals underwater.

23. Echolocation – Whales and Dolphins • Dolphins use sound to detect the size, shape, and speed of objects hundreds of yards away. • So precise it can determine the difference between a golf ball and a ping-pong ball based solely on density FROM: http://www.pbs.org/wnet/nature/episodes/the-dolphin-defender/dolphins-and-sounds/807/

24. Echolocation – How does it work? • Water has superb conduction of sound. • Sound waves travel 4.5 times faster in water than they do in the air. • Using nasal sacs in their heads, dolphins send out rapid clicks that pass through their bulbous forehead, or “melon.” • The sound is focused, then beamed out in front of the dolphin. • The sound wave speeds through the water, bounces off the object under investigation, and is reflected back to the dolphin. FROM: http://www.pbs.org/wnet/nature/episodes/the-dolphin-defender/dolphins-and-sounds/807/

25. Vocabulary • 9. SONAR • 10. SOFAR • 11. Shadow Zone • 12. Bioluminescence • 13. Camouflage • 14. Echolocation • 15. Frequency • Photic Zone • Euphotic Zone • Disphotic Zone • Aphotic Zone • Biological productivity • Thermocline • Eurythermal • Disthermal