34 Water, Waves, and Tides
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WATER, WAVES, AND TIDES
Chapter Outline
NATURE OF WATER
Physical Properties of Water
Structure of a Water Molecule
Chemical Properties of Water
SALT WATER
Composition of Seawater
Salinity
Cycling of Sea Salts
Gases in Seawater
Gasses from Biological Processes
Solubility of Gasses in Seawater
Role of Bicarbonate as a Buffer
OCEAN HEATING AND COOLING
Surface Currents
Classification of Currents
The Ocean Conveyor
Upwelling and Downwelling
Equatorial Upwelling
Coastal Upwelling
Coastal Downwelling
Deepwater Circulation
WAVES
Wave Formation
Types of Waves
Deepwater and Shallow-Water Waves
Breakers
Chapter Objectives
• Describe the basic structure of water.
• Identify the physical properties of water that make it an ideal medium for life.
• Explain the chemical properties of water, including pH.
• Recognize the electrolytes that compose salt water and the concept of salinity.
• Diagram the Coriolis effect.
• Describe the factors that help form surface and deep-ocean currents.
• Classify currents based on their flow patterns and their biological impact.
• Explain the ocean conveyor.
Key Terms
solvent
polar
hydrogen bonds
ion
surface tension
adsorption
oxygen-minimum zone
buffer
greenhouse gases
Coriolis effect
western boundary
currents
Gulf Stream
sverdrup (sv)
eastern boundary currents
wind-induced vertical
transport
upwelling
downwelling
swell
deepwater waves
fetch
shallow-water waves
spring tides
neap tides
diurnal tides
semidiurnal tides
Chapter Summary
1. The unique physical and chemical properties of water make it a critical component
of all living cells. Many of water’s properties are due to the polar nature of the water
molecules and their ability to form hydrogen bonds. Since large bodies of water such
2. Seawater contains a number of salts; sodium chloride is the most abundant. The
salinity of seawater varies with latitude because of evaporation, precipitation,
freezing, thawing, freshwater runoff, and other processes. Evaporation and surf
3. The Earth and its atmosphere receive energy from space in the form of radiant
energy, and return energy to space in the form of heat. An imbalance in the amount
of heat gained and lost can produce global warming or cooling. Excess energy must
4. Winds are produced by differences in the density of air. Warmer air at the equator
rises and moves toward the poles, whereas colder air at the poles sinks and returns
to the equator. Air masses in the northern hemisphere move to the right, and air
5. In some areas of the ocean, seasonal turnover mixes the deeper nutrient-rich,
oxygen-poor water with the oxygen-rich, nutrient-poor surface waters. Wave action
and currents play leading roles in mixing deep and surface waters. Evaporation,
6. Waves are produced by forces acting at the surface of the water, most commonly
wind. The force raises the water, and capillary action or gravity restores the water to
its original position. This combination of events creates a wave. The energy
38 Water, Waves, and Tides
Chapter Outline
I. Nature of Water
A. Most organisms are 70–80% water.
B. Physical properties of water.
1. Water is an excellent solvent.
2. Water has a comparatively high boiling and freezing point.
5. Freezing point and boiling point.
a. Hydrogen bonds.
6. Water as a solvent.
a. Ions.
7. Cohesion, adhesion, and capillary action.
completely absorbed below 10 m, for example.
C. Chemical properties of water.
1. Acid: substance that is a proton (H+) donor.
is basic.
II. Salt Water
A. Composition of seawater.
1. Trace elements.
B. Salinity: concentrations of salt ions dissolved in seawater; ranges between 30 and 35 ppt.
1. Dryer latitudes (30° N and S) have higher evaporation than precipitation, resulting in
C. Cycling of sea salts.
1. Salts are added to ocean through:
a. Volcanic particles added to atmosphere.
d. Rock on seafloor dissolving.
2. Salts are removed from the ocean through:
a. Sea spray.
D. Gases in seawater.
1. O2, CO2, and N2 (see Table 4-3).
2. Biological processes contribute to dissolved gases.
3. Photosynthesis removes CO2 and adds O2.
7. Bicarbonate (HCO3–) serves as a chemical buffer in the ocean.
III. Ocean Heating and Cooling (Refer to Figure 4-9)
A. Earth’s energy budget.
1. Energy input and energy output.
a. Uneven distribution of solar energy, excess at tropics and minimal at
polar latitudes.
2. Sea temperature.
IV. Winds and Currents
A. Winds.
1. Wind patterns.
a. Atmospheric winds.
2. Coriolis effect.
3. Surface wind patterns.
a. Northeastern trade winds.
b. Southeastern trade winds.
B. Ocean currents.
1. Surface currents.
a. Wind energy is transferred to water surface by the friction wind creates
across water.
40 Water, Waves, and Tides
c. Coriolis force (effect) alters the direction of surface water currents
pushing the currents at a 45° angle from prevailing wind direction.
d. Coriolis force pushes water to the right (clockwise) in the northern
hemisphere.
gyre, as the direction is not modified by a continent.
2. Classification of currents.
a. Western boundary currents.
3. The ocean conveyor.
a. Currents below the surface.
V. Ocean Layers and Ocean Mixing
A. Density.
1. Density decreases as water temperature increases and/or salinity decreases.
2. Density increases as water temperature decreases to 4° C and/or salinity
increases.
B. Characteristics of ocean layers.
1. Surface layer.
C. Horizontal mixing.
D. Vertical mixing occurs via thermohaline circulation.
1. Vertical overturn.
2. Isopycnal.
E. Upwelling and downwelling.
VI. Waves
A. Wave formation.
1. Generating force.
2. Restoring force.
3. Capillary waves.
4. Gravity waves.
B. Types of waves.
1. Deepwater and shallow-water waves.
a. Deepwater wave.
3. Tsunami (seismic sea wave).
a. Wave period.
VII. Tides
A. Why tides occur.
1. Generating force: gravitational interaction between the Earth, Moon, and Sun.
2. Centrifugal force.
B. Spring and neap tides.
C. Tidal range.
1. Diurnal tide.
Suggestions for Presenting the Material
1. The content in this chapter is basically divided into atmospheric circulation, surface
ocean circulation (wind-driven currents), thermohaline (density-driven) circulation,
2. Use video clips from the 2003 Oscar-winning surfing documentary Step into Liquid to
illustrate different kinds of waves characterized in the film. From footage of the Bonsai
3. From the Blue Planet series, “The Tidal Seas” has wonderful footage of a tidal bore and
great explanation of how the tides are generated.
4. National Geographic produced a documentary on the December 26, 2004, tsunami from
42 Water, Waves, and Tides
5. The concept of heat redistribution and convection cells is also applicable to global
thermohaline circulation. The clearest explanation of this process for the layman is
Classroom Discussion Ideas
1. Why do wind patterns move in opposite directions in the northern and southern
hemispheres?
2. Explain the importance of water layers mixing.
3. How does the moon affect the tides? What do you think would happen if we did not
have a moon?
Videos, Animations, and Websites
Videos
Step into Liquid.
An Inconvenient Truth. (Documentary, 2006)
A documentary on Al Gore’s campaign to make the issue of global warming a
The Day After Tomorrow. (Movie, 2004)
Tsunami: Killer Wave. (Documentary, 2005)
This documentary covers the formation of tsunamis, including coverage of the deadly
Animations
Savage Seas: Wave Machine.
Websites
Smithsonian: Ocean Planet.
Ocean’s Alive: Oceans in Motion.
National Oceanographic and Atmospheric Administration.
Information on tides and tidal predictions.
SaltWaterTides.Com.
Tide tables for US coasts.
NOAA Center for Tsunami Research.
Research on predicting tsunamis.
National Oceanographic and Atmospheric Administration.
Information on El Niño events.
Suggested Answers to End of Chapter Questions
Multiple Choice
1. b. the ability of water molecules to form hydrogen bonds
2. a. acids
44 Water, Waves, and Tides
Matching
1. c.
5. a.
9. b.
Short Answer
1. What roles do photosynthesis and respiration play in the distribution of gases in
seawater?
Photosynthesis removes carbon dioxide from seawater and adds oxygen into
seawater. Respiration removes oxygen from seawater and adds carbon dioxide, the
2. What factors are responsible for the prevailing wind patterns of the Earth?
The factors responsible for prevailing wind patterns are differential solar heating
3. What combination of factors produces neap tides?
Neap tides result from the Earth being at a right (90°) angle from the moon and the
4. Explain how the polar nature of water molecules influences water’s physical
characteristics.
The chemical bonds in the water molecule are polar covalent; electrons are shared
between the atoms but not shared equally. The oxygen atom exerts a stronger
5. Explain how salt from the sea is returned to the land.
Sources for the ions (salts) dissolved in seawater include sediments from
weathered continental rock, volcanic activity, and biological activity. The most
6. Explain how vertical mixing of seawater occurs.
Vertical mixing of seawater is density-driven. Seawater density increases as
salinity increases and temperature decreases. Denser water sinks and less dense
46 Water, Waves, and Tides
7. Describe how winds are produced.
The Earth’s surface winds are a result of differential solar heating on Earth’s
surface, forming convection cells (warm air rising and cool air falling) at regular
8. Explain how waves are formed.
Waves are generated when a disturbing force is applied to the ocean surface. The
9. Explain how breakers are formed.
Breakers (waves) form when the bottom of the wave interacts with the ocean
10. Describe how upwellings occur.
Upwelling occurs when atmospheric winds cause surface ocean water to diverge.
11. What is the biological importance of upwelling and downwelling zones?
Upwelling causes nutrient- and oxygen-rich bottom water to surface. An increase
in nutrients produces increased algal and zooplankton populations in upwelling
Chapter 4 47
12. What are gyres and how are they formed?
Gyres are large, circular surface ocean patterns that carry warm water from the
tropics to the poles and cool water from higher latitudes toward the tropics. The
13. Why is carbon dioxide more soluble in seawater than oxygen?
Carbon dioxide is more soluble in seawater because it dissociates in water to form
14. List three different processes that circulate water in the oceans.
Surface currents (gyres), upwelling and downwelling, and density-driven
15. Why is the shallow-water thermocline in polar and temperate seas seasonal?
The shallow-water thermocline is seasonal because the solar input at higher
Thinking Critically
1. Would it be easier for a planktonic organism to float in water with a high salinity or a
low salinity? Explain.
For an organism to float in the ocean, it must have a lower density than seawater.
2. Why do upwelling zones and downwelling zones support more biomass than areas of
the open sea where these zones don’t exist?
Upwelling zones support more biomass than areas of the open ocean because
48 Water, Waves, and Tides
3. Why do coastal cities usually experience cooler summers and warmer winters than
cities of the same latitude that are inland?
Coastal cities enjoy a more moderate climate than inland cities at similar latitudes
4. Sometimes the discharge of organic wastes from land into coastal waters results in a
phytoplankton bloom. How would this affect organisms that live in the water below the
surface and on the bottom?
High concentrations of phytoplankton deplete nutrients (nitrogen and
5. What effect do you think boundary currents have on coastal communities of
organisms?
Warm western boundary currents (western side of ocean basin) would produce
Suggested InfoTrac® Articles
“The Role of Thermohaline Circulation in Abrupt Climate Change.” Clark, P.U., N.G.
Pisins, T.F. Stocker, and A.J. Weaver. Nature, (2002).