Light and Sound
Aquatic Science 2011
K. Schneider
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
Classification by Light
• Photic zone – Sunlight top layer
of ocean.
Two divisions:
1. Euphotic
zone
2. Disphotic
zone
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
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
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
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
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
Warm-up
• Describe the photic zone and it’s 2
subdivisions (zones).
• What color acts best as camouflage in the
Twilight Zone. Why?
Sound
http://video.pbs.org/video/1777525840
1. What term describes the transmission of
sounds by the dolphins?
2. How does it work?
factsofworld.com
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
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
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
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
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
SONAR
• SOund Navigation And Ranging
• 2 Types of SONAR
– Active
– Passive
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
Shadow Zone
• A region into which very little sound energy
penetrates
• Created when sound waves arrive at the highvelocity layer, split and refract to the surface or
bend into the depth.
• An object beyond that area where it splits may not
be detected
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.
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.
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/
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/
Vocabulary
1.
2.
3.
4.
5.
6.
7.
8.
Photic Zone
Euphotic Zone
Disphotic Zone
Aphotic Zone
Biological productivity
Thermocline
Eurythermal
Disthermal
9. SONAR
10. SOFAR
11. Shadow Zone
12. Bioluminescence
13. Camouflage
14. Echolocation
15. Frequency