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Chapter 9 Pages 9-3 to 9-15
The Physics of Water
The Physics of Water
9-2
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The Physics of Water
Chapter 9 Page 9-3
The Physics of Water
 Seawater’s chemical properties affect how life
functions in the ocean.
 Water’s physical properties not only affect life
processes of marine organisms, but of human beings
in the water.
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Chapter 9 Pages 9-3 to 9-6
The Physics of Water
Heat and Heat Capacity
 Temperature is crucial in determining where
organisms can live in the ocean.
 The concept of temperature comes from the need to
measure the relative heat of two bodies, or the same
body after removing or adding heat.
 Suppose you’ve filled a bathtub with warm water and
scooped out a glassful. If you take the temperatures
of the water in the glass and the water in the tub,
you’ll find they are the same. But, which has more
heat?
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Chapter 9 Pages 9-3 to 9-6
The Physics of Water
Heat and Heat Capacity
 Heat is the kinetic energy in the random
movement, or vibration, of individual atoms and
molecules in a substance.
 The faster molecules move, the more heat there
is. Total heat energy is measured based on both
the quantity and speed of vibrating molecules.
 Temperature measures only how fast the
molecules vibrate.
 The two most common temperature systems are
Fahrenheit and Celsius. Celsius is most used in
science because it is based on water’s physical
properties.
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Chapter 9 Pages 9-3 to 9-6
The Physics of Water
Heat and Temperature
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Heat and Heat Capacity
Chapter 9 Pages 9-3 to 9-6
The Physics of Water
 Heat capacity of a substance is the amount of
heat energy required to raise a given amount of a
substance by a given temperature.
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Heat and Heat Capacity
Chapter 9 Pages 9-3 to 9-6
The Physics of Water
 Scientists express heat capacity in terms of the
amount of heat energy it takes to change one
gram of a substance by 1°C.
 It’s expressed as the number of calories required.
 It takes more heat energy to raise water’s
temperature than that of most substances.
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Heat and Heat Capacity
Chapter 9 Pages 9-3 to 9-6
The Physics of Water
 Therefore water can absorb or release a lot of heat
with little temperature change.
 Water’s heat capacity affects the world’s climate and
weather.
 Heat is carried to areas that would otherwise
be cooler, and heat is absorbed in areas that
would otherwise be hotter.
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Chapter 9 Pages 9-3 to 9-6
The Physics of Water
Heat and Heat Capacity
 A great example is the island of Bermuda. Bermuda
has a moderately tropical climate year round, even
though it lies above 30° north latitude. That’s about
the same latitude as Birmingham, Alabama, or Fort
Worth, Texas, both of which experience some snow
and freezing rain in the winter.
 The difference is that the warm Gulf Stream
current flows around Bermuda.
 By carrying so much heat north, the Gulf Stream
gives Bermuda a tropical climate.
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Chapter 9 Pages 9-3 to 9-6
The Physics of Water
Heat and Heat Capacity
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Water Temperature and Density
Ice
Chapter 9 Pages 9-7 to 9-8
The Physics of Water
 As water cools it becomes denser.
 At 3.98°C (39.16°F) it reaches maximum density.
Below this point, it crystallizes into ice. As water
moves into a solid state* it becomes less dense.
Liquid Water
* State is an expression of a substance’s
form as it changes from solid, to liquid, to gas
with the addition of heat.
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 Ice does not form all at once at the freezing point of 0°C (32°F),
but crystallizes continuously until all liquid turns solid.
Temperature does not drop any further until all the liquid water
freezes, even though heat continues to leave.
 This produces non-sensible heat – a change in heat
energy that cannot be sensed with a thermometer.
 The non-sensible heat lost when water goes from liquid to
solid state is called the latent heat of fusion.
 Sensible heat is that which you can sense with a
thermometer.
Chapter 9 Pages 9-7 to 9-8
The Physics of Water
Water Temperature and Density
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Water Temperature and Density
Chapter 9 Pages 9-7 to 9-8
The Physics of Water
Relationship
of Density to
Temperature
in Pure Water
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Water Temperature and Density
Chapter 9 Pages 9-7 to 9-8
The Physics of Water
Relationship of Density
to Temperature
in Most Substances
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Latent Heat of Vaporization
Chapter 9 Pages 9-9 to 9-11
The Physics of Water
 Latent heat of vaporization is the heat required to
vaporize a substance.
 It takes more latent heat to vaporize water than to
freeze it because when water freezes only some
of the hydrogen bonds break.
 When it vaporizes, all the hydrogen bonds must
break, which requires more energy.
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Latent Heat of Vaporization
Changing from a solid to a
liquid.
Chapter 9 Pages 9-9 to 911
The Physics of Water
Changing from a liquid to
a vapor.
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Latent Heat of Vaporization
Chapter 9 Pages 9-9 to 9-11
The Physics of Water
Latent Heat of
Vaporization
and Fusion
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Latent Heat of Vaporization
Chapter 9 Pages 9-9 to 9-11
The Physics of Water
Hydrological Cycle
Shows the Movement of
Water Around the Earth
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Thermal Inertia
Chapter 9 Pages 9-11 to 9-12
The Physics of Water
 The tendency of water to resist temperature
change is called thermal inertia.
 Thermal equilibrium means water cools at about
the same rate as it heats.
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Chapter 9 Pages 9-11 to 9-12
The Physics of Water
Thermal Inertia
 These concepts are important to life and Earth’s
climate because:
 Seawater acts as a global thermostat, preventing
broad temperature swings.
 Temperature changes would be drastic between night
and day and between summer and winter.
 Without the thermal inertia, many – perhaps most –
of the organisms on Earth could not survive the
drastic temperature changes that would occur each
night.
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Ocean Water Density
Chapter 9 Pages 9-13 to 9-14
The Physics of Water
 Seawater density varies with salinity and
temperature.
This causes seawater to stratify, or form
layers.
Relationship Between
Temperature, Salinity
and, Density
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Ocean Water Density
Chapter 9 Pages 9-13 to 9-14
The Physics of Water
 Dense water is heavy and sinks below less dense
layers. The three commonly found density layers are:
 Surface zone – varies in places from absent to 500 meters
(1,640 feet). In general it extends from the top to about 100
meters (328 feet). This zone accounts for about only 2% of
the ocean’s volume.
 Thermocline – separates the surface zone from the deep
zone. It only needs a temperature or salinity difference to
exist. This zone makes up about 18% of the ocean’s volume.
 Deep zone – lies below the thermocline. It is a very stable
region of cold water beginning deeper than 1,000 meters
(3,280 feet) in the middle latitudes, but is shallower in the
polar regions. The deep zone makes up about 80% of the
ocean’s volume.
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Density
Layers
Chapter 9 Pages 9-13 to 9-14
The Physics of Water
Ocean Water Density
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Chapter 9 Pages 9-13 to 9-14
The Physics of Water
Ocean Water Density
 The relatively warm, low-density surface waters are separated
from cool, high-density deep waters by the thermocline, the
zone in which temperature changes rapidly with depth.
 The top of the thermocline varies with season, weather,
currents, and other conditions.
 It depends in part on the amount of heat the surface zone
receives from the sun and is therefore more pronounced in
tropical and temperate waters.
 Thermoclines are weaker in polar regions because the
surface water there is cold.
 Thermocline zones account for about 18% of ocean water.
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Chapter 9 Pages 9-13 to 9-14
The Physics of Water
Ocean Water Density
 Below the thermocline is the deep layer. This layer is
cold, dense, and fairly uniform because it originates
in the polar regions.
 It begins deeper than about 1,000 meters (3,280
feet) in the middle latitudes but becomes
shallower until it reaches the surface in the polar
regions.
 The deep zone makes up about 80% of the
ocean’s volume.
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Chapter 9 Pages 9-16 to 9-33
How Water Physics Affect Marine Life
How Water Physics Affect Marine Life
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Chapter 9 Pages 9-16 to 9-20
How Water Physics Affect Marine Life
Light
 Water scatters and absorbs light. When light
reaches the water’s surface, some light penetrates,
but, depending on the sun’s angle, much may simply
reflect back out of the water.
 Within the water, light reflects off light-colored
suspended particles.
 Dark colored suspended particles and algae
absorb some of the light.
 Water molecules absorb the energy, converting
light into heat.
 Water absorbs colors at the red end of the
spectrum more easily than at the blue end.
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Chapter 9 Pages 9-16 to 9-20
How Water Physics Affect Marine Life
Light
Reflection,
Scattering, and
Absorption
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Chapter 9 Pages 9-16 to 9-20
How Water Physics Affect Marine Life
Light
Natural Light
Artificial Light
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Chapter 9 Pages 9-16 to 9-20
How Water Physics Affect Marine Life
Light
 Two zones exist with respect to light penetration:
 Photic Zone – where light reaches (can be as deep as 590
meters/1,968 feet). The photic zone has two subzones.
 Euphotic Zone – the upper shallow portion where most
biological production occurs – comprises about 1%
of the ocean.
 Dysphotic Zone – where light reaches, but not enough
for photosynthetic life.
 Aphotic Zone – it makes up the vast majority of the ocean.
Where light does not reach and only a fraction of marine
organisms live.
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Chapter 9 Pages 9-16 to 9-20
How Water Physics Affect Marine Life
Light
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Chapter 9 Pages 9-21 to 9-22
How Water Physics Affect Marine Life
Temperature
 Seawater doesn’t fluctuate in temperature nearly as
much as air does.
 Marine organisms rarely encounter temperatures
below 1.9°C or above 30°C. Compared to landbased climates, this narrow range provides an
advantage.
 Compared to land-based climates, marine
organisms live in a much less challenging
environment with respect to temperature
range.
 Generally, temperature dictates the rate of chemical
reaction.
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Chapter 9 Pages 9-21 to 9-22
How Water Physics Affect Marine Life
Temperature
 Most marine organisms have an internal temperature
close to that of surrounding seawater.
 Their internal temperature changes with seawater
temperature. An organism with this characteristic
is called an ectotherm.
 Ectotherms are commonly called cold-blooded
organisms, and include terrestrial as well as
marine organisms.
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Chapter 9 Pages 9-21 to 9-22
How Water Physics Affect Marine Life
Temperature
 Other marine organisms, such as certain tuna and sharks, have
an internal temperature that varies, but remains 9˚ to 16˚C
warmer than the surrounding water. Organisms with this
characteristic are called endotherms.
 Marine mammals and birds have an internal temperature that is
relatively stable. Organisms with this characteristic are called
homeotherms.
 Some endotherms have a body temperature above their
surroundings, but it is not constant and varies with the
surrounding temperature. Organisms with this characteristic are
called poikilotherms.
 Endotherms are commonly called warm-blooded
organisms.
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Chapter 9 Pages 9-21 to 9-22
How Water Physics Affect Marine Life
Temperature
 Temperature affects metabolism – the higher the
temperature within an organism the more energyreleasing chemical processes (metabolism)
happen.
 Endotherms and homeotherms can tolerate a wide
range of external temperatures.
 Internal heat regulation allows endotherms an
advantage.
 Their metabolic rate remains the same regardless
of external temperature allowing them to live in a
variety of habitats.
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Chapter 9 Pages 9-22 to 9-24
How Water Physics Affect Marine Life
Sound
 Sound is energy that travels in pressure waves.
 It can only travel through matter, which is why
there’s no sound in outer space.
 Sound travels well in air, but even better in
water.
 In distilled water at 20˚C/68˚F, sound travels 1,482.4
meters (4,863.4 feet) per second, which is about five
times faster than in air.
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Chapter 9 Pages 9-22 to 9-24
How Water Physics Affect Marine Life
Sound
 Travels through warm water faster than cool…
but it travels faster in deep water due to pressure.
 Bounces off suspended particles, water layers,
the bottom and other obstacles.
 Travels much farther through water
than light does.
 Is eventually absorbed
by water as heat.
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Sound
Chapter 9 Pages 9-22 to 9-24
How Water Physics Affect Marine Life
 Because sound travels so well in water, marine
mammals use echolocation to sense an object’s
size, distance, density, and position underwater.
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 Right now, you’re under pressure. If you’re at sea
level, you’re under the pressure of the atmosphere,
which is literally the weight of the air.
 Water weighs far more than air, so marine organisms
exist in an environment with greater surrounding
pressure than land-based organisms do.
Chapter 9 Pages 9-25 to 9-28
How Water Physics Affect Marine Life
Pressure
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Chapter 9 Pages 9-25 to 9-28
How Water Physics Affect Marine Life
Pressure
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 Pressure exerted by water is called hydrostatic pressure.
It’s simply the weight of the water.
 At 10 meters (33 feet) hydrostatic pressure is equal to
atmospheric pressure – 1 bar/ata.
 At 10 meters (33 feet) the total pressure is 2 bar – 1 bar from
atmospheric pressure plus 1 bar from hydrostatic pressure.
 A marine organism living at 10 meters (33 feet) experiences
twice the pressure present at sea level. Pressure increases
1 bar for each additional 10 meters (33 feet).
Chapter 9 Pages 9-25 to 9-28
How Water Physics Affect Marine Life
Pressure
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How Water Physics Affect Marine Life
Chapter 9 Pages 9-25 to 9-28
Pressure
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How Water Physics Affect Marine Life
Chapter 9 Pages 9-25 to 9-28
Pressure
 Hydrostatic pressure doesn’t affect marine
organisms because it is the same inside the
organism as outside.
 Living tissue is made primarily of water, which
(within limits) transmits pressure evenly. Since it’s
in balance, pressure doesn’t crush or harm
marine organisms.
 Hydrostatic pressure is primarily an issue only for
organisms that have gas spaces in their bodies.
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How Water Physics Affect Marine Life
Chapter 9 Pages 9-25 to 9-28
Pressure
 Many fish have a gas bladder that they use to control their
buoyancy.
 They must add or release gas from the bladders when they
change depth to keep the pressure in balance.
 Similarly, scuba divers learn to add air to the space in their
ears (a technique called equalizing because it equalizes the
pressure inside the air space with the pressure outside),
which allows them to dive without discomfort.
 Failure to equalize can cause the
pressure to rupture the diver’s
ear drums.
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Chapter 9 Page 9-27
How Water Physics Affect Marine Life
Pressure and Gas Volume Relationships
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Chapter 9 Page 9-28
How Water Physics Affect Marine Life
Size and Volume
 Marine organisms thrive by getting all the resources they need
from the water around them.
 Each cell gets the nutrients and gas it needs from the
surrounding environment and excretes waste products into
that environment.
 Single-cell organisms, such as protozoa or bacteria, make
these exchanges directly to and from seawater.
 A multicellular organism, such as a sea cucumber or a fish,
uses systems to gather nutrients and gas from the
environment and excrete waste.
 The cells within a multicellular organism make the
exchanges via the organism’s systems rather than directly
with the surrounding water.
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 High surface-to-volume ratio is important for cell
function. The bigger the cell, the lower the
surface-to-volume ratio, which means that there’s
less relative area through which to exchange
gases, nutrients, and waste.
 This is why large organisms are multicellular
rather than a giant single cell.
Chapter 9 Page 9-28
How Water Physics Affect Marine Life
Size and Volume
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 Using a sphere to substitute for a cell:
 The volume of a sphere increases with the cube of
its radius and the surface area increases with the
square of its radius.
 If a cell were to increase diameter 24 times
original size, the volume would increase 64
times, but the surface area would increase
only 16 times.
Chapter 9 Page 9-28
How Water Physics Affect Marine Life
Size and Volume
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Buoyancy
Chapter 9 Pages 9-29 to 9-31
How Water Physics Affect Marine Life
 Archimedes’ Principle states that an object
immersed in a gas or liquid is buoyed up by a force
equal to the weight of the gas or liquid displaced.
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How Water Physics Affect Marine Life
Chapter 9 Pages 9-29 to 9-31
Buoyancy
Floats
Sinks
Floats
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 Means marine organisms don’t have to expend
much energy to offset their own weight compared
to a land-based existence.
 It allows entire communities to exist simply by drifting.
 It allows organisms to grow larger than those on land.
 It allows many swimming creatures to live without
ever actually coming into contact with the bottom.
Chapter 9 Pages 9-29 to 9-31
How Water Physics Affect Marine Life
Buoyancy
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How Water Physics Affect Marine Life
Chapter 9 Pages 9-29 to 9-31
Buoyancy
Buoyancy Makes Size Possible
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Chapter 9 Pages 9-31 to 9-32
How Water Physics Affect Marine Life
Movement and Drag
 While marine organisms have an advantage over
land-based organisms with respect to buoyancy, the
situation is reversed when it comes to drag.
 Because water has a far higher viscosity than air,
it resists movement through it far more than air
does.
 Consider what happens when you’re in a
swimming pool; it takes very little effort to push
yourself off the bottom thanks to buoyancy.
 However, it takes far more effort to swim a long
distance than to run the same distance. This is
due to drag.
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Chapter 9 Pages 9-31 to 9-32
How Water Physics Affect Marine Life
Movement and Drag
 Viscosity affects small
organisms, plankton in particular.
 Their small size gives them little
strength to swim through water.
 Small marine organisms avoid sinking by:
 Plumes, hairs, ribbons, spines, and other
protrusions that increase their drag and help them
resist sinking.
 Others have buoyancy adaptations that help them
remain suspended in the water column (oil in
tissues).
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Chapter 9 Pages 9-31 to 9-32
How Water Physics Affect Marine Life
Movement and Drag
 Some marine organisms need to overcome drag as
they swim. Adaptations that help them overcome
drag:
 Moving or swimming very slowly.
 Excreting mucus or oil that actually lubricates
them to “slip” through the water.
 The most common is to have a shape that reduces
drag – streamlining.
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Chapter 9 Pages 9-31 to 9-32
How Water Physics Affect Marine Life
Movement and Drag
Drag, Streamlining, and Turbulence
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Chapter 9 Pages 9-32 to 9-33
How Water Physics Affect Marine Life
Currents
 It is speculated that drifting provides several
advantages.
 Drifting disperses organisms into new habitats,
ensuring survival should something happen to the
original community.
 May take organisms into nutrient-rich areas,
preventing too many offspring from competing for
the same resources in the original community.
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