Chapter 18 Oceanography

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Chapter 18 Oceanography
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18.1 The Seafloor

• Ocean Basin Features
• The continental shelf is a gradually sloping end
  of a continent that extends out under the ocean
• Along some coasts it can extend long distances
• Atlantic and gulf coasts 100 to 350 km
• Pacific Coast 10 to 30 km

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• The continental slope is the end of the continent
  extending form the outer edge of the shelf down
  to the ocean floor
• The slope is steeper than the shelf
• Beyond the slopes lie the trenches, valleys,
  plains and ridges
• Abyssal plains are the flat seafloors in the deep
  ocean, formed by deposition of sediment by ocean
  currents
• 4000 to 6000 km deep in the ocean

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• Plate Boundary Structures
• The place where new ocean floor forms is called
  the mid-ocean ridge
• Resembles a chain of mountains
• Magma from the Earths interior oozes from these
  cracks
• Seamounts are inactive volcanic cones found on
  the ocean floor
• Seamounts that extend up out of the ocean are
  volcanic islands.

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• On the ocean floor crustal plates converge at
  trenches
• A trench is a long, narrow steep-sided depression
  in the ocean floor where one crustal plate is
  forced beneath another
• Most trenches are found in the Pacific Basin
• Often longer and deeper than any valley on any
  continent
• Not only are they deepest places on Earth, they
  are also the most geologically active
• Seaquakes and chains of volcanoes often occur
  along trenches

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• Mining the seafloor
• There are many petroleum and natural gas deposits
  in continental shelf sediments
• About 20 of the worlds oil comes from under the
  seabed
• Other deposits on the continental shelf are also
  mined
• Placer deposits form where rivers meet oceans and
  can no longer carry their sediments
• Sand, metals, and even diamonds are mined from
  placer deposits in some regions

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• Valuable minerals are also found in deep water
• Minerals can form where molten substances and hot
  water are forced into cool ocean water
• Other minerals precipitate out and form solids on
  the ocean floor

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18.2 Life in the Ocean

• Life Processes in the Ocean
• All life is water based
• Life began in the oceans
• Water is used for all the basic processes of
  living things
• Nearly all the energy used by organisms
  ultimately comes from the sun
• Chlorophyll-containing organisms use the suns
  energy to make food

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• Another type of food web in the ocean does not
  depend on sunlight
• In areas along the mid-ocean ridges, bacteria
  produce food and oxygen by using dissolved sulfur
  compounds that escape from magma (chemosynthesis)
• Ocean water also provides an easy way for
  organisms to reproduce
• Seawater also provides a thermally stable
  environment for organisms

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• Ocean Life
• Plankton are tiny marine algae and animals that
  drift with currents
• Nekton are animals that actively swim, rather
  than drift with the currents
• Nekton include all swimming forms of fish and
  other animals
• Some deep dwelling organisms have special
  light-generating organs for attracting live food
• Benthos are bottom dwellers
• plants, algae, and animals that live on the
  seafloor
• Some are attached, others burrow

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• Corals are organisms that live attached to the
  seafloor
• Obtain food by stinging their prey
• A reef is a rigid, wave-resistant structure built
  from skeletal materials and calcium carbonate

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18.3 Pollution and Marine Life

• Ocean Pollution
• Pollution is the introduction by humans of
  harmful waste products, chemicals, and substances
  into an environment
• A pollutant is a substance that causes damage to
  an organism by interfering with biochemical
  processes
• Most ocean pollution is concentrated along the
  coasts

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• Industrial waste sometimes gets into seawater
• Solids such as plastic bags can entangle animals
• Pesticides used in farming and on lawns run off
  and reach the ocean
• Crop fertilizers and sewage can reach the oceans
  and cause rapid growth of some algae
• Oil from oil spills and wastewater can pollute
  the ocean
• Soil and silt can also accumulate in coastal
  areas due to erosion upstream