Addison-Wesley  Earth Science – Terms and Definitions - Chpt.8

                     Authors: Robert E. Fariel, Robert W. Hinds, David B.Berey

   

   

   Chapter 8                    The Ocean

   Section  1                    The Bottom of the Ocean

   

   abyssal plain                   Large flat area of the deep sea floor; formed by sediment
   flows that spill off the continental margins.

   continental margin           The region of the ocean bottom near the land areas; contains most
   of the sediment eroded from the land; separates a continent from the deep sea floor.

   echo sounding                A method of using noise (pings) to measure the depth of the
   ocean.

   

   island arc                        A chain of islands, usually curved, that separates a
   marginal sea from a major ocean.

   marginal sea                   A smaller body of salt water found along the margin of a major
   ocean.

   mid-ocean ridge             A system of rugged mountains that extends down the middle of the
   ocean basins.

   ocean                             The entire body of salt water that covers much of the
   earth's surface; also, any of its major geographical divisions.

   ocean basin                    The low-lying earth formation that contains the ocean's water;
   consists mainly of dense basaltic crustal rock.

   rift valley                        Deep valley in the center of the mid-ocean ridge; a site of
   active volcanism.

   Ring of Fire                    The region of volcanic activity that surrounds the basin of
   the Pacific Ocean.

   trench                             A long narrow depression of the deep sea floor; generally
   has steep sides; usually bordered by areas of volcanic activity.

   guyot                              A flat topped under water mountain.

   seamount                        Volcanic cone growing upward from the ocean bottom layer by
   layer, usually rising more than 1000m above the floor.

   

   

   

   Section 2             Properties of Ocean Water

   aphotic zone                   The part of the ocean that is in total darkness.

   disphotic zone                A zone of reduced light in the ocean; between 200m and 1000m
   deep.

   freezing point                  The temperature at which a liquid freezes.

   icebergs                         Floating masses of ice that broke off fresh water glaciers.

   pack ice                         Sea ice that has been broken and then refrozen into jagged
   pressure ridges.

   photic zone                     The uppermost zone of the open ocean and the zone of most
   light.

   salinity                            Saltiness; a measure of the amount of total dissolved
   materials in water; grams of dissolved materials per kilogram of water.

   sea ice                            Frozen ocean water.

   water mass                     A large volume of water characterized by a similar temperature,
   salinity, and density throughout its mass.

   water pressure                The force that a mass of overlying water exerts upon a submerged
   surface.

   

   Section 3             The Circulation of Ocean Water

   crest                                The highest point of a wave.

   gyre                                 A closed system of rotating ocean currents.

   high tide                           When the waterline of a body of water reaches its highest
   point.

   low tide                           When the waterline of a body of water reaches its lowest
   point.

   rogue wave                      A very high wave that forms on the open ocean when high waves
   of about the same wavelength have their crests coincide.

   surf zone                          The area where breaking waves occur.

   swell                                A rhythmic pattern of waves.

   trough                              The lowest point between two wave crests.

   tsunami                            A huge wave caused by an underwater earthquake somewhere
   along the ocean bottom; barely noticeable out at sea.

   upwelling                         A process by which deep, cold, nutrientrich water is brought
   to the surface and replaces lighter surface water.

   wave base                       The point below the surface of water at which the orbital
   motion of a wave nearly disappears (1/2 a wavelength below the midheight of the wave).

   wave height                     The vertical distance between a wave´s highest and lowest
   points.

   wavelength                      The horizontal distance from a point on one wave to the
   corresponding point on the next wave.