AEROBE 



aerobe — (also called aerotiont). An organism 

 which can live and grow only in the presence of 

 oxygen. An organism which employs aerobic 

 respiration. 



aerobiont — See aerobe. 



A-frame — A steel frame used for outboard sus- 

 pension of oceanographic gear in shipboard sur- 

 vey work, so named because of its A-shape. 



afternoon effect — ^The solar heating of the surface 

 water, which causes a shallow negative tempera- 

 ture gradient. The net result is downward 

 refraction of sound rays and reduction in near- 

 surface ranges. 



aftershock — An earthquake which follows a 

 larger earthquake and originates at or near the 

 focus of the larger earthquake. ( 2 ) 



age — 1. See age of phase inequality. 



2. The stage of development of sea ice. The 

 term usually refers to the length of time since its 

 formation and to its thickness. 



age dating — The calculation of the absolute age 

 of a material by such means as the fossil record 

 or by radioactive determination of the number 

 of atoms of a stable radiogenic end product rela- 

 tive to the nimiber of atoms of its radioactive 

 parent. 



age of diurnal inequality — (or age of diurnal 

 tide). The time interval between the maximum 

 semimonthly north or south declination of the 

 moon and the maximum effect of the declination 

 upon the range of tide or speed of the tidal 

 current. (50) 



age of diurnal tide — See age of diurnal inequal- 

 ity. 



age of moon — The time elapsed since the preced- 

 ing new moon. ( 50) 



age of parallax inequality — The time interval 

 between the perigee of the moon and the maxi- 

 mum effect of the parallax (distance of the 

 moon) upon the range of tide or speed of tidal 

 current. (50) 



age of phase inequality — (or age, age of tide). 

 The time interval between the new or full moon 

 and the maximum effect of these phases upon the 

 range of tide or speed of tidal current. (50) 



age of tide — See age of phase inequality. 



age of water — The time elapsed since a water mass 

 was last at the surface and in contact with the 

 atmosphere. The water's age gives an indica- 

 tion of the rate of overturn of ocean water, an 

 important factor in the use of the oceans for 

 dumping radioactive wastes and determining 

 the rate of replenishment of nutrients. 



The most commonly used method for deter- 

 mining the age of water involves the decay 

 rate of carbon" whose half-life is 5,600 years. 

 This method gives the following approximate 

 ages to an accuracy of ±100 years: North 

 Atlantic Central Water, 600 years.; North At- 

 lantic Bottom Water, 900 years; North Atlantic 

 Deep Water, 700 years ; Antarctic Intermediate 



and Bottom Water (South Atlantic), less than 

 350 years. 



Another method for determining the age of 

 water makes use of the depletion rate of dis- 

 solved oxygen. This method assumes that the 

 water was saturated with oxygen while at the 

 surface and that its oxygen was consumed at a 

 fixed rate by chemical combination with detritus. 

 (45) 



agger — See double tide. 



agglomerate — see breccia. 



aggradation — The process of building up a sur- 

 face by continuous or intermittent deposition. 



aggregate sample— iS^ee compound sample. 



agonic line — The line through all points on the 

 earth's surface at which the magnetic declina- 

 tion is zero; that is, the locus of all points at 

 which magnetic north and true north coincide. 

 This line is a particular case of an isogonic line. 

 The position of this line exhibits variations in 

 time. (5) 



agua enferma — See aguaje. 



aguaje — (also called salgaso, aqua enferma) . An 

 annual condition noted in the coastal water of 

 Peru which results in discolored water (usually 

 red or yellow) and various degrees of destruc- 

 tion of marine life. Aguaje usually occurs 

 from April through June and is a local term 

 used along certain portions of the Peruvian 

 coast. The immediate cause of this condition is 

 the increase in water temperature when warmer 

 oceanic currents are carried inshore. Marine 

 organisms unaccustomed to warm water die and 

 decompose. Coincidentally large concentra- 

 tions of dinoflagellates form discolored water 

 patches. Dinoflagellates, in turn may destroy 

 marine organisms, possibly due to toxins they 

 contain. This is not the same as the massively 

 catastrophic condition associated with El Niiio 

 which occurs approximately every seven years. 



Agulhas Current — (sometimes called Agulhas 

 Stream). A fast current flowing southwest- 

 ward along the southeast coast of Africa. 



Throughout the year, part of the South 

 Equatorial Current turns south along the east 

 coast of Africa and feeds the strong Agulhas 

 Current. To the south of 30°S the Agulhas 

 Current is a narrow, well-defined current that 

 extends less than 100 kilometers from the coast ; 

 south of 35°S a major portion of the current 

 turns counterclockwise and joins the prevailing 

 eastward flow across the southern part of the 

 Indian Ocean. However, a small portion of the 

 Agulhas Current rounds the Cape of Good Hope 

 into the Atlantic Ocean. 



Agulhas Stream — See Agulhas Current. 



aid to navigation — 1. A device external to a boat 

 or ship designed to assist in determination of 

 position, a safe course, or to warn of dangers. 

 Examples are: lighthouses, lights, buoys, day- 

 beacons, radio beacons, and electronic devices. 

 (51) 



