Oceans: The Last Frontier introduces oceanography with a brief discussion of the extent and distribution  of the world ocean. After examining the composition of seawater, the ocean's layered temperature and salinity structures are presented. The ocean floor section of this chapter begins with an examination of continental margins and continues with submarine canyons and associated turbidity currents, ocean basin features, and mid-ocean ridges. The origin of coral reefs and atolls is also presented. The chapter ends with a discussion of sea floor sediments and how they are used to study climatic changes.

 

Learning Objectives

 

After reading, studying, and discussing the chapter, students should be able to:

 

·         Understand the extent and boundaries of the world’s oceans.

·         Briefly discuss the chemical composition of ocean water.

·         Discuss the ocean's layered temperature and salinity structures.

·         Compare and contrast the features of active and passive continental margins.

·         List and define the features of the ocean basin floor.

·         Briefly discuss the types of sea floor sediments.

·         Explain how ocean floor sediments are related to climate changes.

 

Chapter Outline___________________________________________________________________

 

 

    I.  The world ocean

       A.  Extent

             1.  71% of Earth

             2.  61% of the Northern Hemisphere

             3.  81% of the Southern Hemisphere

       B.  Size and depth of the major oceans

             1.  Pacific is by far the largest

             2.  Pacific has greatest average depth

             3.  Atlantic the shallowest

       C.  Composition of seawater

             1.  3.5% (by weight) dissolved minerals

             2.  Salinity

                  a.  Proportion of dissolved salts

                  b.  Units: parts-per-thousand (‰)

                  c.  Salinity of ocean: 33‰-37‰

                  d.  Major constituents: Cl^- and Na^-+

             3.  Sources of salts

                  a.  Chemical weathering of rocks

                  b.  Outgassing

       D.  The ocean's three-layered structure         

            1.  Temperature

                  a.  Warmest at surface

                  b.  Thermocline

                      1.  Below surface zone

                      2.  Rapid decrease with depth

                  c.  Below thermocline - little change

             2.  Salinity

                  a.  In low and middle latitudes

                      1.  Higher at surface

                      2.  Fresh water is evaporated

                  b.  Halocline

                      1.  Below surface zone

                      2.  Rapid decrease with depth

                  c.  Below halocline - little change

 

  II.  Mapping the ocean floor

       A.  Measuring depth is often done with an echo sounder

       B.  Shape of the ocean surface is measured by satellites

    

       A.  Passive continental margins

             1.  Continental shelf

             2.  Continental slope

             3.  Continental rise

                  a.  Turbidity currents

                  b.  Deep-sea fans

       B.  Active continental margin

             1.  Continental slope descends into a deep-ocean trench

             2.  Located around the Pacific Ocean

 

IV.  Submarine canyons and turbidity currents

       A.  Submarine canyons originate on the continental slope and are not due to stream erosion

       B.  Turbidity currents, dense sediment laden water, are thought to excavate submarine canyons

 

  V.  Deep-ocean basins

       A.  Deep-ocean trenches

             1.  Deepest parts of ocean

             2.  Where plates plunge into mantle

       B.  Abyssal plains

             1.  Most level places on Earth

             2.  Thick accumulations of sediment

       C.  Seamounts

             1.  Isolated volcanic peaks

             2.  Some form over hot spots

 

VI.  Mid-ocean ridges

       A.  Sites of sea-floor spreading

       B.  Found in all major oceans

       C.  Rift valleys, down-faulted structures

 

VIII.  Sea floor sediments

       A.  Thickness varies

       B.  Mud is the most common sediment

       C.  Types

             1.  Terrigenous sediment–weathered rocks

             2.  Biogenous sediment-shells, etc.

             3.  Hydrogenous sediment-chemical deposits

       D.  Seafloor sediments and climatic change

             1.  Life in the sea changes with climate

             2.  Fossils record the changes