Karleskint Small Turner Chapter 4 Water, Waves, and Tides.
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Transcript of Karleskint Small Turner Chapter 4 Water, Waves, and Tides.
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Chapter 4Chapter 4Water, Waves, and TidesWater, Waves, and Tides
• 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)
Sea sprayremoves
salts
Bottom sediments
Precipitation
Precipitation
Chloride (Cl–)Sulfate (SO4
2–)
Hydrogen sulfide (H2S)
Chlorine (Cl2)
Volcano
Sulfur
Organismsdie
Calcium (Ca2+)Magnesium (Mg2+)
Potassium (K+)
Rock onthe seafloor
Clay particlesadsorb
Riverdischarge
Carbonate (CO32–)
Calcium (Ca2+)Sulfate (SO4
2–)
Sodium (Na+)Magnesium (Mg2+)
Salts removedwhen organisms are
caught for food
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 western-boundary 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 OceanStrong 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
• 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.