Chapter 18 Oceanography

1. Chapter 18 Oceanography

2. 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

3. 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

4. Plate Boundary Structures • The place where new ocean floor forms is called the mid-ocean ridge • Resembles a chain of mountains • Magma from the Earth’s 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.

5. 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

6. Mining the seafloor • There are many petroleum and natural gas deposits in continental shelf sediments • About 20% of the world’s 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

7. 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

8. 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 sun’s energy to make food

9. 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

10. 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

11. 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

12. 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

13. 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