Chapter 13 – Oceans and Beaches How do oceans shape our lives?
I. Distribution of Water on Earth <ul><li>1. 97% of all water on Earth is salt water </li></ul><ul><li>2. Only 3% is freshwater, including icebergs, lakes, rivers, and groundwater. </li></ul><ul><li>A. Water covers 71% of Earth’s surface </li></ul>
B. The major oceans of the world are the Pacific (51.6% of ocean water); the Atlantic (23.6 %) and the Indian Ocean (21.2%). Therefore other oceans and seas only account for 3.6% of water on Earth.
II. Properties of Ocean Water <ul><li>A. Ocean water is a mixture of gases and solids dissolved in pure water. </li></ul><ul><li>B. There are 85 elements found to exist in ocean water. </li></ul><ul><ul><li>1. Salinity describes the amount of dissolved salts in ocean water. It is expressed in parts per thousand , with the average being 35 parts per thousand. </li></ul></ul>
2. The most abundant salt is sodium chloride , NaCl. A liter of seawater will contain about 2.5 teaspoons of this common salt. 3. The second most abundant salt is magnesium chloride .
4. Other elements found in ocean water include sulfur, calcium, potassium, bromine, carbon, strontium, silicon, fluorine, aluminum, phosphorous, and iodine.
<ul><li>C. The most abundant gases in ocean water are nitrogen, carbon dioxide and oxygen . The amount of dissolved gases is affected by two things: </li></ul>
1. Depth- the greater supply of gases at the ocean’s surface is due to the penetration of sunlight . This allows photosynthesis to take place which ensures a large supply of oxygen .
2. Temperature of ocean water- warm water holds less dissolved gas than cold water. This means that denser cold water sinks, carrying oxygen to deep areas of the oceans while allowing animals to live there.
a. The warmest layer of the ocean is the surface zone where water is mixed by waves and currents.
b. The thermocline is the zone below the surface where rapid temperature change occurs .
c. The coldest layer is the deep zone with temperatures of around 5 degrees Celsius.
III. Motions of the Ocean <ul><li>A. Waves are the movement of energy through a body of water. </li></ul>
B. Most waves are formed by winds blowing over the surface of the ocean. This transmits energy to the water, forcing it to ripple.
<ul><li>C. The size of a wave depends on three things: </li></ul><ul><ul><li>1. The strength of the wind </li></ul></ul><ul><ul><li>2. The distance the wind blows (called the fetch) </li></ul></ul><ul><ul><li>3. The length of the gust (duration) </li></ul></ul>
<ul><li>D. Waves are divided into several parts </li></ul><ul><li>Crest- the highest point of the wave. </li></ul><ul><li>2. Trough- the valley between two waves </li></ul>
3. Wavelength- the horizontal distance between the crests or troughs of two consecutive waves 4. Wave height- a vertical distance between a wave’s crest and the next trough
5. Wave period- measures the size of the wave in time
E. Ocean waves caused by earthquakes are called tsunamis .
F. Water below the surface moves in streams called currents . These currents are caused by two factors: wind patterns and water density .
1. Surface currents are caused by wind patterns and usually have a depth of several hundred meters. These currents affect climate and weather patterns by warming or cooling the air above the water
a. The Gulf Stream is known as a long-distance surface current that carries warm water from the southern tip of Florida along the eastern coast of the US.
b. Currents in the Northern Hemisphere move clockwise (currents correspond to the wind circulation in each hemisphere), while currents in the Southern Hemisphere move counterclockwise
i. The Coriolis effect (the apparent shift in fluids or objects due to the rotation of the Earth) explains ocean current patterns curving in each hemisphere.
ii. Ex. You are sitting on a carousel tossing a ball to someone on the edge of the carousel. After tossing the ball, the target person has moved on and the ball passes behind them. From the target person’s perspective, the ball appears to have curved away. This explains the Coriolis effect .
c. Surface currents that travel over short distances are called short-distance currents . These currents are usually found at shorelines.
i. Currents moving parallel to the shore are called longshore currents. As these currents move they carry large amounts of sand creating sand bars .
ii. A rip current occurs when a current cuts an opening in a sand bar and the currents return to the ocean in a powerful, narrow flow (a type of undertow).
<ul><li>2. Deep currents are movements of water deep under the surface of the oceans and are caused mainly by differences in water densities . </li></ul><ul><ul><li>a. The density (heaviness of the water) is affected by temperature and salinity. </li></ul></ul>
<ul><li>Cold water is more dense than warm water </li></ul><ul><li>ii. The saltier the water, the more dense </li></ul>
b. Deep currents usually flow in opposite directions from surface currents.
c. The movement of deep ocean currents to the surface is called upwelling . This occurs when deep cold currents are forced upward by the ocean floor bringing nutrient rich foodstuffs to the surface. This produces rich fishing grounds in areas where upwelling occurs. (Ex. Peru, Chile)
d. El Niño (Spanish for "the Christ Child") refers to a warm ocean current that typically appears around Christmas-time and lasts for several months, but may persist into May or June. The warm current influences storm patterns around the globe.
i. Upwelling ceases to occur when winds die down. Without the nutrient rich waters, many fish and sea creatures die, devastating the fishing industry. ii. Without upwelling, the water becomes much warmer changing weather patterns globally .
Review Questions 1. How are waves created? wind
2. Explain how the Coriolis effect influences surface currents. Currents in the Northern Hemisphere turn clockwise. Currents in the Southern Hemisphere turn counter clockwise.
3. Why is upwelling important to aquatic life? Because colder water holds more dissolved gases and nutrients. When the cold water comes up, the fish come with it.
IV. Shoreline Formation <ul><li>A. Shorelines are the natural boundary between the land and ocean created by the action of natural processes such as storms, tides, changing sea levels, the outflow of materials from rivers, and the work of plants and animals. </li></ul>
<ul><li>B. Shorelines are constantly changing landscapes due to powerful waves constantly eroding rocks and depositing sediments to reshape the land. </li></ul><ul><li>The following are examples of shoreline formations: </li></ul><ul><ul><ul><li>1. Sea Cliffs- steep faces of rocks </li></ul></ul></ul>
2. Caves - hollowed out portions of sea cliffs
3. Sea Stacks- columns of resistant rocks left standing
4. Sand Bars- an underwater ridge of sand created by longshore currents
<ul><li>5. Beaches- waves deposit large amounts of rock particles to form our beaches </li></ul><ul><ul><li>a. The backshore is the area of the shoreline above the high water or high tide mark. This can contain cliffs or sand dunes or a berm (flat upper beach). </li></ul></ul>
b. The foreshore is the area that is exposed at low tide . It may have a beach scarp (vertical slope produced by wave erosion) and a low tide terrace (broad flat area exposed at low tide).
c. The offshore region extends from the low tide mark seaward beyond the wave breaking zone. It has a shoreface (slope below the low tide mark) and a longshore trough (a depression parallel to the beach between the low tide mark and wave breaking zone).
6. Barrier Islands- (nature’s way of straightening out the shore) elongated bodies of sand bounded on either end by inlets allowing salt and fresh water to flow into and out of the estuary behind the island. (Ex. Outer Banks )
Review Questions <ul><li>1. What processes are continually changing our shorelines over time? </li></ul>Waves Storms Tides Changing sea levels currents
2. What natural process must occur in order to create our beaches? Wind, waves and currents
3. Hypothesize how you think North Carolina’s barrier islands (Outer Banks) were created over time. Surface currents
V. The North Carolina’s Barrier Islands- The Outer Banks <ul><li>A. Barrier islands form in response to four factors: </li></ul><ul><li>1. A rising sea level - Melting of ice caps formed during ice ages caused a change in sea levels beginning about 10,000 years ago. The sea level was 300 to 400 feet below its present level. The following is an example of sea level changes creating barrier islands. </li></ul>
a. A straight coast forms during lower sea levels. b. Rising sea levels flood valleys on land and creates a sinuous coast. c. Sand eroded from preexisting ridges forms spits ( sandbar connected to a curving shoreline ) d. The spits are breached by storms, separating the islands from the mainland.
2. A large supply of sand - 15,000 years ago the sea level was much lower, waves and winds formed beach ridges (dunes) on the coast of North Carolina. Sea levels rose and broke through the dune forming a lagoon , and the dune is now isolated as an island.
3. A gently sloping coastal plain - North Carolina’s coast slopes at .2 feet per mile. The underlying geology of North Carolina consists of sediments dating of Quaternary age (1.8 million years ago to present) with older sediments buried underneath. The deposition of these sediments created a gentle slope conducive to forming barrier islands.
4. Sufficient wave energy to move sand. Kitty Hawk
B. After barrier islands form, the islands then begin to migrate landward in response to rising sea levels (currently 1 foot per century).
1. Humans are increasing the rate of barrier island migration through erosion by building structures to prevent property damage. One example is seawalls . Seawalls steepen the slope of the beach, which increases wave size. This eventually leads to the loss of beaches. (Four states, including North Carolina in 1985, now prohibit shoreline armoring )
2. The Cape Hatteras lighthouse is evidence that shorelines change over time and will continue to do so.
<ul><li>C. After World War II, the outer banks began to be heavily developed leading to many problems and threats to coastal residents. </li></ul><ul><ul><li>1. Hurricanes and winter storms are a constant threat to shore residents. The estimated property damage by Hurricane Fran in 1996 is 4.1 billion dollars. </li></ul></ul>
2. Pollution- Improper waste disposal , closing of fishing grounds due to pollution, and drinking water contamination after storms are just a few of the problems in coastal North Carolina.
3. Environmental Destruction- The beaches of North Carolina are being destroyed due to overdevelopment .
VI. The Truths of the Shoreline <ul><li>A. Beach erosion is an expected part of barrier island evolution, especially as sea levels rise. </li></ul><ul><li>B. Shoreline erosion is not a problem until someone builds a structure by which to measure it. </li></ul>
C. Shoreline erosion does not create problems for the beach, it simply changes its position . D. Human activities such as building seawalls, dune construction, building construction, channel dredging, reduce the beaches’ sand supply. This increases the rate of shoreline retreat.
E. Shoreline engineering protects the interests of few people , who are causing the erosion to begin with, and is a high cost to state and federal governments.
F. “You can have buildings, or you can have beaches; in the long run you cannot have both”. The ultimate truth is to avoid the hazards and evaluate the level of risk if choosing to build on a barrier island or coastline.
Review Questions 1. Explain the four factors that create barrier islands. -rising sea level -large supply of sand -gently sloping coastal plain -sufficient wave energy to move sand
2. How are humans increasing the rate of barrier island migration? -building sea walls -dune construction -building construction -channel dredging
3. How would you advise a business executive that wants to develop a large chain of hotels on the coastline of the Outer Banks? Do not build on the Outer Banks!