Transcript Chapter 4 - Perry Local Schools

Chapter 4
Water, Waves, and Tides
Karleskint
Turner
Small
• 71% of Earths surface is covered with
water
• 97% salt water
• 3% fresh water
Nature of Water
• Marine organisms are 70 – 80% water by
mass.
• Terrestrial organisms are approximately
66% water by mass!
• Physical properties of water
–
–
–
–
–
excellent solvent
high boiling point and freezing point
denser in its liquid form than in its solid form
supports marine organisms through buoyancy
provides a medium for chemical reactions necessary
for life
Nature of Water
• Structure of a water molecule
– 2 H atoms bonded to 1 O atom
– polar - different parts of the molecule have
different electrical charges:
• the oxygen atom carries a slight negative charge;
the hydrogen atoms carry a slight positive charge
Nature of Water
• Specific heat (Thermal capacity)
– ocean can maintain relatively constant
temperature
• Water and light
– much light reflected into the atmosphere
– different wavelengths (colors) of light penetrate
to different depths
Nature of Water
• Chemical properties of water
– pH scale measures acidity/alkalinity
– ocean’s pH is slightly alkaline (average 8)
– organisms’ internal and external pH affect life
processes such as metabolism and growth
Salt Water
• Salinity
– seawater = 3.5% salt, 96.5% water
– expressed as in g per kg water or parts per
thousand (ppt)
– salinity of surface water varies as a result of
evaporation, precipitation, freezing, thawing,
and freshwater runoff from land
– areas around 30o N and 30o S = high salinity
(evaporation > precipitation)
– poles = high salinity (freezing – removes water
from sea)
Hydrogen sulfide (H2S)
Chlorine (Cl2)
Sulfur
Volcano
Precipitation
River
discharge
Organisms
die
Chloride (Cl–)
Sulfate (SO42–)
Sea spray
removes
salts Salts removed
Calcium (Ca2+)
when organisms are Magnesium (Mg2+)
caught for food
Carbonate (CO32–)
Potassium (K+)
Calcium (Ca2+)
Sulfate (SO42–)
Sodium (Na+)
Clay particles
Magnesium (Mg2+)
adsorb
Precipitation
Bottom sediments
Rock on
the seafloor
Stepped Art
Fig. 4-6, p. 75
Salt Water
• Gases in seawater
– gases from biological processes
• oxygen is a by-product of photosynthesis
• release of CO2 from respiration
• oxygen-minimum zone – located just below sunlit
surface waters
– solubility of gases in seawater
• seawater has more O and CO2 but less N than the
atmosphere
• affected by temperature, salinity and pressure
Ocean Heating and Cooling
• Sea temperature
– temperature varies daily and seasonally
– affected by energy absorption at the surface,
loss by evaporation, transfer by currents,
warming/cooling of atmosphere, heat loss
through radiation
– seasonal variations in the amount of solar
radiation reaching the earth, occur especially
between 40o and 60o N and S because angle
of sun’s rays change dramatically at these
latitudes seasonally
Winds and Currents
• Winds
– result from horizontal air movements caused
by temperature, density, etc.
– as air heats, its density decreases and it rises;
as it cools, density increases and it falls
toward earth
– wind patterns: upper air flow from the equator
towards the north and south
Winds and Currents
• Winds
– Coriolis effect
• Apparent force on moving particles resulting from
the earth’s rotation
• path of air mass appears to curve relative to the
earth’s surface—to the right in the Northern
Hemisphere, left in the Southern
Winds and Currents
• Surface wind patterns
– 3 convection cells in each hemisphere:
• northeast & southeast trade winds
• westerlies
• polar easterlies
– areas of vertical air movement between wind
belts
• Doldrums (at equator)
• horse latitudes (at 30o N & S)
Winds and Currents
• Ocean currents
– surface currents
• driven mainly by trade winds (easterlies and
westerlies) in each hemisphere
• Coriolis effect
– deflection can be as much as 45-degree angle from wind
direction
• gyres—water flow in a circular pattern around the
edge of an ocean basin
Winds and Currents
• Classification of currents
– western-boundary currents: fastest, deepest
currents that move warm water toward the poles in
each gyre (e.g. Gulf Stream)
– eastern-boundary currents: slow moving, carry cold
water toward the equator
– transverse currents: connect eastern- and westernboundary currents in each gyre
– biological impact
• western-boundary currents not productive, carry little
nutrients, but increase oxygen mixed in water
• eastern-boundary currents productive, nutrient-rich
Winds and Currents
• Currents below the surface
– energy transferred from winds to surface
water is transferred to deeper water
– deeper-water currents are deflected by the
Coriolis effect, down to about 100 m
– friction causes loss of energy, so each layer
moves at an angle to and more slowly than
the layer above, creating an Ekman spiral
– Ekman transport—net movement of water to
the 100-m depth
Ocean Layers and Ocean Mixing
• Density increases when salinity increases
• Density increases when temperature
decreases
Ocean Layers and Ocean Mixing
• Characteristics of ocean layers
– depth 0-100 m (330 feet): warmed by solar
radiation, well mixed
– 100-1,000 m: temperature decreases
– thermocline – zone of rapid temperature
change
– halocline: salinity increases 0-1,000 m
– pycnocline: 100-1,000 m, where changes in
temperature and salinity create rapid
increases in density
– seasonal thermoclines
Ocean Layers and Ocean Mixing
• Horizontal mixing
– winter temperatures and increased salinity
owing to freezing result in very dense water at
the poles, which sinks toward the ocean floor
Ocean Layers and Ocean Mixing
• Vertical mixing
– isopycnal—stable water column that has the
same density from top to bottom
– vertical mixing allows water exchange
between surface and deep waters
– nutrient-rich bottom water is exchanged for
oxygen-rich surface water
Ocean Layers and Ocean Mixing
• Upwelling and downwelling
– equatorial upwelling
• water from currents on either side of the equator is
deflected toward the poles, pulling surface water
away to be replaced by deeper, nutrient-rich water
– coastal upwelling
• Ekman transport moves water offshore, to be
replaced by deeper, nutrient-rich water
– coastal downwelling
• coastal winds force oxygen-rich surface waters
downward and along the continental shelf
Ocean Layers and Ocean Mixing
• Deepwater circulation
– differences in density, not wind energy, cause
water movement in deep oceans
– dense Antarctic water sinks to the bottom and
moves slowly toward the Arctic
Waves
• Wave formation
– wave: a flow of energy or motion, not a flow of
water
– generating force: a force that disturbs the
water’s surface, e.g., wind, geological events,
falling objects, ships
Waves
• Types of waves
– Progressive (forced) waves are generated by
wind and restored by gravity, progress in a
particular direction
• forced waves are formed by storms, which determine
their size and speed
• free waves, no longer affected by the generating
force, move at speeds determined by the wave’s
length and period
• swells are long-period, uniform free waves which
carry considerable energy and can travel for
thousands of km
Waves
• Types of Waves (con’t)
– deepwater and shallow-water waves
• deepwater waves—waves that occur in water that
is deeper than ½ of a wave’s wavelength
– breakers
• deepwater waves become shallow-water waves
when they move into shallow water
• surf zone—area along a coast where waves slow
down, become steeper, break, and disappear
• breakers form when the wave’s bottom slows but
its crest continues at a faster speed
Waves
• Types of Waves (con’t)
– Tsunamis (large seismic sea waves)
• seismic sea waves are formed by earthquakes
• tsunamis have long wavelengths, long periods and
low height
• compression of the wave’s energy into a smaller
volume upon approaching a coast or island causes
a dramatic increase in height
Tides
• Tides: periodic changes in water level
occurring along coastlines
• Why tides occur
– tides result from the gravitational pull of the
moon and the sun
– though smaller, the moon is closer to earth, so
its gravitational pull is greater
– water moves toward the moon, forming a bulge
at the point directly under it
– the centrifugal force opposite the moon forms
another bulge
– areas of low water form between bulges
Tides
• Spring and neap tides
– during spring tides, the times of highest and
lowest tides, the earth, moon and sun are in a
line and act together creating highest and
lowest tides
– when the sun and moon are at right angles,
the sun’s pull offsets the moon’s, resulting in
neap tides, which have the smallest change
between high and low tide
Tides
• Tidal range
– diurnal tide: one high tide and one low tide each
day
– semidiurnal tide: two high tides and two low
tides each day (most common)
• mixed semidiurnal tide: high and low tides are at
different levels
– flood tides are rising; ebb tides are falling
– tidal currents are associated with tidal cycle
– slack water occurs during the change of tides
Climate and the Ocean
Ocean is a great modifier of temperature
Hydrologic cycle
• Convection, evaporation, and precipitation
Weather
Front - when cold air mass collides with a
warm air mass
• Fronts are marked by stormy weather
Monsoons
Seasonal wind pattern changes caused by
heating or cooling on the continents
• Summers - significant rainfall and winters very little
Common on the west coast of India and in
Southeast Asia
Cyclones
• Large rotating storm systems of low-pressure air
Forms over warm oceans near Equator
• Typhoons – Pacific Ocean
• Hurricanes – Atlantic Ocean
Strong rotating winds
• At least 74 miles per hour
• Thunder and Lightning
• Winds rotate in a counterclockwise direction
around a central, calm eye
When it moves over land (or cold water) the
storm begins to weaken quickly
• Storm is fueled by warm water
Average 100 cyclones worldwide each year
• Weather symbol for a
hurricane is:
• Marine flags that warn
of a hurricane
Hurricane Structure
Eye – relatively calm
• roughly 20 to 30 miles wide
Smaller the eye – stronger the winds
Right side generally has the fastest winds
Left side usually has the most rain
Hurricane Classification
5 categories based on current maximum wind
speed
Saffir-Simpson Hurricane Scale
• Category 1 – Winds 74-95 mph
• Category 2 – Winds 96-11 mph
• Category 3 – Winds 111-130 mph
• Category 4 – Winds 131-155 mph
• Category 5 – Winds over 155 mph
– Very rare, status for a short time
Storm Surges
Becoming more dangerous due to increase
in coastal population
Waterspouts
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Tornado over water
May carry water as high as 328 ft
Very short-lived
Not particularly dangerous
Most often occur during the summer
months
• Florida Keys have the most in the U.S.