KarleskintKarleskint

SmallSmall

TurnerTurner

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.