GLOSSARY GLOSSARY Abyssal - deep portions of the ocean, typically below Bed load (&action load) - quantity of bottom sediment 2000 fa (3700 m). transported by a current through traction, that is by Abyssal hills - small elevations (often extinct volcanoes) saltation, rolling, and sliding. distributed over large tracts of the seafloor. Benthic - pertaining to the bottom terrain of oceanic Abyssalplain - a flat or gently sloping, almost featureless regions. region of the deep ocean overlain with sediments. Bloom - a rapid growth of phytoplankton in spring and Acceleration ofgravity @) -the rate of change with time of fall that causes large temporary concentrations of the the velocity of an object caused by the earth’s gravita- organism. Can result in discolored or toxic water tional force. known as red tide. (See Plankton). Advection - the transport of a property (e.g. heat or salt) Bore (hydraulicjump)- an almost vertical, solitary wave by fluid motions such as currents or winds. front caused when the water speed associated with the Aerobic - conditions where free oxygen is present; re- crest begins to exceed the translation speed of the wave. quires free oxygen for organic existence and growth. Waves on beaches commonly deform into a bore prior Amphidromicpoint- a point at which there is no tide and to breaking. The water flow associated with a bore around which the cotidal lines rotate over a tidal cycle. changes abruptly from a region of low depth and high Tidal amplitudes (corange lines) increase outward speed to one of high depth and low speed with a series from this point to cover an area called the amphidromic of undulations behind the leading crest (see Tidal region. bore). Amplitude - the magnitude or half-cycle displacement of Bottomfiction - the retarding force on water moving a wavelike fluctuation as measured from its mean or over the bottom. It increases with increased roughness equilibrium value. The amplitude of an ocean wave is of the bottom, current speed, and degree of turbulence half its trough-to-crest height, or the height from the in the water. still water level to the wave crest; in the case of the tide, Brackish water - water having a salinity of 0.50-17%0, amplitude equals half the range. common to nearsurface estuarine environments from Anaerobic - lacking in free oxygen. Certain bacteria can late spring to early autumn. live in such conditions. Buoyancy - the net upward force exerted on an object or Andular momentum - the momentum of a particle or parcel of fluid due to the difference in density between parcel of water arising from its rotation about an axis. it and the surrounding fluid; quantitatively equal to the Its value is proportional to the particle’s mass, linear weight of the water displaced by the object. velocity, and distance from the rotation axis. Anomalistic month - the average period of the moon’s orbit around the earth with respect to the lunar per- Cat’spaw- a puff of wind; a light breeze that temporarily igee; equal to about 27.55 days. ruffles patches of the water surface. Anticyclonic - a sense of rotation opposite to that of the Chop - short-crested waves that spring up following earth’s rotation; clockwise in the northern hemisphere onset of a moderate breeze, and break readily at the and counterclockwise in the southern hemisphere. crest. Antinode (antinodal line, antinodal point) - the position Coastalplain - a plain composed of gently sloping or flat (or line) of maximum displacement in an oscillating strata of sedimentary material fronting the coast and region ofwater. The region midway between two nodal generally derived from a recently emerged portion of lines in a standing wave pattern. the sea bottom. Apogee - position in the moon’s orbit that is hrthest Cobble - a water-worn rock fragment between 64 and from the earth (opposite to perigee). 256 mm in diameter, larger than a pebble but smaller Asthenosphere (or mantle) -the region of the earth with than a boulder. plastic-flow characteristics between the crust Constituent,tidal - a harmonic (sinusoidal) contribution (lithosphere) and the core. in a mathematical expression for the tide-generating Attenuation - a reduction in wave amplitude. force used to specify a selected cycle in the tide or tidal current. Each constituent has a fixed period but an amplitude that is determined by observation or Backing - a change in the wind or current direction in a through a model. counterclockwise sense (opposite to Eering). Continentalmagin - the portion of the seafloor adjacent Bar - an elongate ridge of sand, gravel, or other uncon- to the continent and separating it from the deep sea. solidated material built in shallow water by the action The continental margin includes the continental rise, of waves and currents, especially at the mouth of a river continental slope, and continental shelf or estuary. Convective overturn - the process by which the surface Basalt - a fine-grained, dark-coloured igneous rock. The waters, cooled sufficiently by the air to make them oceanic crust and granitic continents are thought to be more dense than underlying waters, sink and are re- underlain by basaltic material. placed by an upward motion of less dense water. In the - 249 - subarctic Pacific region of the North Pacific Ocean, the edge oftwo regions with different current speeds or overturning takes place in winter but is limited to the directions. upper 100 m ofwatcr due to the presence ofthe pcrma- Edge wave - a near-shore (shore edge) wave with an nent halocline between 100 and 200 m. accompanying pattern of horizontal currents that pro- Corange line - a line joining regions of equal tide range. gresses parallel to the coast with crests normal to the Coriolisfirce (Coriolis effect) -an apparent force due to the coastline. Wave heights diminish rapidly seaward ofthe earth's rotation that acts at right angles on a moving coast. object or fluid. The force is proportional to the speed Embayment - a shoreline indentation that forms an open and latitude of the object, is zero at the equator and a bay. maximum at either pole for a fixed speed. Entrainment - the process by which relativelv high-den- Cotidal line - a line joining regions with simultaneous sity fluid is incorporated into an overlying layer of less occurrence of high water. Synonymous with cophase dense fluid as a result of breaking wavelike disturbances line. or turbulent motions at the interface between the flu- Countercurrent - a surface current parallel to, but setting ids. In an estuary, entrainment produces at net trans- in the opposite direction to, the main current. port ofsalt from the saline ocean water to the overlying Crust - see Lithosphere. brackish layer. Cusp - one of a series of low mounds of beach material Epicenter - the point on the earth's surface directly above separated by crescent-shaped troughs spaced at the point of origin (focus) of an earthquake. roughly equal intends along a beach. Equilibn'um the09 - a model of the tide that assumes a Cyclonic - a sense of rotation in the same sense as that of continuous ocean of uniform depth over the earth in the earth's; counterclockwise in the northern hemi- which the water responds instantl!r to the tide-generat- sphere and clockwise in the southern hemisphere. ing forces ofthe sun and moon. Land masses, bottom friction, and inertia are ignored in the model. Equilibrium tide - the hypothetical tide generated by the tidegenerating forces in the equilibrium theory of the - the time for one rotation of the earth. There are Day tide. Also called the gravitational tide or astronomical different types of day depending on whether the sun, tide. moon, or a star is used as the point of reference for the rotation; solar day (24 h), lunar day (24.84 h), and sidereal day (23.93 h), respectively. Fan - a relatively smooth, fan-shaped feature that nor- Dead water - the condition whereby a vessel expends mall\i slopes away from the lower termination of a considerable propulsive power in the generation of an canyon or canyon system. Also, deep-sea fan and sub- internal wake as it travels in a region with a shallow marine fan. brackish layer overlying a deeper more saline layer. Fault - a fracture or fracture zone in rock along which Declination - the angle that the sun, moon, or other relative movement of opposing sides has occurred. celestial object subtents with the plane of the earth's Fetch - the area of the ocean surface where seas are equator. generated by a wind with nearly constant direction and Density - the ratio of the mass of any substance to the speed. Also, the spatial extent of this area measured in volume it occupies. Typical ocean water has densities in the wind direction. the approximate range of 1.020-1.028 g/cm3. Flocculation - the process by which fine particles of clay Diatom - a single-celled plant (phytoplankton) covered suspended in fresh water aggregate into lumps on con- with two overlapping porous shells of silica. Diatoms tact with salt water and settle out of suspension; a are one of the most abundant marine organisms and a depositional mechanism common to estuarine regions. primary source of food in the sea. Fracture zone - an extensive linear zone of irregular Dispenion - the separation of a group (or packet) of seafloor topography characterized by steep-sided or waves into component parts due to differences in prop- asymmetrical ridges, troughs, or escarpments. agation speeds of the waves. Frequency - a measure of the number of oscillations or Diurnal - meaning daily and pertaining to motions cycles per unit time; the reciprocal ofthe time duration which complete a cyclic pattern every solar or lunar day. (period) of an oscillation. (A wall outlet in North Dnjit current - a broad, slow ocean current principally America for example, has a voltage oscillation fre- driven by the large-scale winds.