abioseston — See tripton. 



ablation — 1. The combined processes (such as sub- 

 limation, melting, evaporation) which remove 

 snow or ice from the surface of a glacier, snow- 

 field, etc. ; in this sense, the opposite of alimen- 

 tation. Particularly in glaciology, the term 

 may be applied to reduction of the entire snow- 

 ice mass, and may also include losses by wind 

 action and by calving. 



Air temperature is the dominant factor in con- 

 trolling ablation; precipitation amounts exer- 

 cise only secondary control. During the abla- 

 tion season, an ablation rate of about two milli- 

 meters per hour is typical of most glaciers. 



2. The amount of snow or ice removed by the 

 above processes; in this sense, the opposite of 

 accumulation. 

 (5) 



abnormal — Opposed to normal in whatever sense 

 the latter term is used. Wlien normal signifies 

 typical, abnormal means unusual, lying outside 

 the range of common occurrence. When normal 

 signifies an arithmetic mean or median value, 

 abnormal implies a deviation, however slight, 

 from the mean or median. (5) 



abrasion — The wearing away or rounding of sur- 

 faces by friction; for example, the action of 

 glaciers, wind, and waterborne sand on rocks 

 or rock fragments. 



abrasion platform — A surface of marine denuda- 

 tion formed by wave erosion which is still in its 

 original position at or near the wave base, with 

 the marine forces still operating on it. 



absolute index of refraction — See index of re- 

 fraction (sense 1). 



absolute refractive index — See index of refrac- 

 tion (sense 1). 



absolute temperature scale — (abbreviated A). 

 See Kelvin temperature scale. 



absorptance — The ratio of the radiant flux lost 

 from a beam by means of absorption to the in- 

 cident flux. (8) 



absorption — 1. The process in which incident ra- 

 diant energy is retained by a substance. A fur- 

 ther processs always results from absorption, 

 that is, the irreversible conversion of the ab- 

 sorbed radiation into some other form of energy 

 within and according to the nature of the ab- 

 sorbing medium. The absorbing medium itself 

 may emit radiation, but only after an energy 

 conversion has occurred. 



A substance which absorbs energy may also be 

 a medium of reflection, refraction, diffraction, 

 or scattering ; these processes, however, involve 

 no energy retention or transformation and are 

 to be clearly differentiated from absorption. 

 See attenuation. 



2. In general, the taking up or assimilation of 

 one substance by another, where the two sub- 

 stances chemically or physically combine. 

 (5) 



absorption coefficient — 1. A measure of the 

 amount of normally incident radiant energy 

 absorbed through a unit distance or by a mass 

 of absorbing medium. (5) 



2. For dissolved gases: Maximum volume of 

 gas that can be dissolved in a unit volume of 

 water. The absorption coefficient of gases gen- 

 erally decreases with increasing temperature and 

 salinity. 



absorption factor —See absorptivity. 



absorption loss — That part of the transmission 

 loss which is due to dissipation or the conversion 

 of sound energy into some other form of energy, 

 usually heat. This conversion may take place 

 within the medium itself or upon a reflection at 

 one of its boundaries. (3) 



absorptivity — (also called absorption factor). 

 A measure of the amount of radiant energy ab- 

 sorbed by a given substance of definite dimen- 

 sions ; defined as the ratio of the amount of ra- 

 diant energy absorbed to the total amount inci- 

 dent upon that substance. (5) 



abyss — A particularly deep part of the ocean, or 

 any part below 300 fathoms. (68) 



abyssal — (or dbyssohenthic) . Pertaining to the 

 great depths of the ocean, generally below 2,000 

 fathoms (3,700 meters). {See figure for clas- 

 sification of marine environments.) 



abyssalbenthic — According to some authorities 

 corresponding to the approximate lower half of 

 the bathyal and all of the abyssal and hadal. 

 See classification of marine environments. 



Pertaining to a deep sea zone extending below 

 400 to 600 fathoms (800 to 1,100 meters) and 

 comprising all of the deep sea benthic system 

 below the archibenthic zone. 



abyssal gap — This term is not recommended by 

 ACUF. ^S'eegap. 



abyssal hill — This term is not recommended by 

 ACUF. ^ee knoll. 



abyssal plain — This term is not recommended by 

 ACUF. ^ee plain. 



