ALEXANDER'S ACRES 



The Aleutian low is most intense in the winter 

 months; in summer it is disjDlaced toward the 

 North Pole and is almost nonexistent. On a 

 daily basis, the area of the Aleutian low is 

 marked by alternating high and low pressure 

 centers, moving generally to the eastward; it is 

 not the scene of an intense stationary low. (5) 



Alexander's Acres — An unusual, but easily rec- 

 ognizable type of deep scattering layer record 

 (possibly caused by tent fish) in which the train 

 of echoes forms a series of crescentic or mound- 

 shaped traces. This type of layer record usually 

 occurs at a depth of about 180 fathoms and has 

 been recorded most consistently in the slope 

 water off the northeastern United States by 

 means of an echo sounder using 12-kc sound. 



alga(e) — A thallophyte possessing chlorophyll ; 

 includes almost all seaweeds. See red alga, 

 blue-green alga, brown alga, green alga. 



algal ball — See algal biscuits. 



algal biscuits — (also called algal hall^ marl hall). 

 Spherical and disk-shaped bodies up to 20 centi- 

 meters in diameter, composed of algal lime- 

 stone and often dolomitic. (2) 



algal limestone — A limestone composed largely of 

 the remains of calicum-secreting algae. (2) 



algal reef — A reef composed largely of algal re- 

 mains. 



algal ridge — The elevated margin of a windward 

 reef built by actively growing calcareous 

 algae. (2) 



algal rim — A low rim built by actively growing 

 calcareous algae on the lagoonal side of a lee- 

 ward reef, or on the windward side of a reef 

 patch in a lagoon. ( 2 ) 



alignment — (also spelled alinement) . In a near- 

 shore wave study, a line drawn on a chart par- 

 allel to the general direction of a section of 

 coast. Tlie waves calculated to strike the mid- 

 point of the alignment are assumed to be char- 

 acteristic of those reaching the shallow water 

 of the entire section. 



alignment chart — See nomogram. 



alimentation — Generally, the process of provid- 

 ing nourishment or sustenance ; thus in glaciol- 

 ogy, the combined processes which serve to in- 

 crease the mass of a glacier or snowfield; the 

 opposite of ablation. The deposition of snow 

 is the major form of glacial alimentation, but 

 other forms of precipitation along with sub- 

 limation, refreezing of melt water, etc. also 

 contribute. 



The additional mass produced by alimenta- 

 tion is termed accumulation. (5) 



alinement — See alignment. 



alkalinity — In sea water, the excess of hydroxyl 

 ions over hydrogen ions, generally expressed as 

 milliequivalents per liter. ( 5 ) 



allochem — Marine sediment formed by chemical 

 or biochemical precipitation; includes intra- 

 clasts, oolites, fossils, and pellets. (2) 



allogenic — The term applied to rock or sediment 

 constituents which originated at a different 

 place and at a previous time to the rock of which 

 they now constitute a part. Examples are 

 pebbles in a conglomerate. 



alluvium — The detrital deposits eroded, trans- 

 ported, and deposited by streams ; an important 

 constituent of shelf deposits. 



alpha particle — 1. A positively charged particle 

 emitted from a nucleus and composed of two 

 protons and two neutrons. It is identical in all 

 measured properties with the nucleus of a helium 

 atom. 



2. By extension, the nucleus of a helium atom, 

 especially when it is in rapid motion, as when 

 artificially accelerated. 

 (41) 



alpha ray — A synonym for alpha particle, (70) 



alternating current — See reversing current, 

 tidal current. 



altitude — 1. The vertical distance between a point 

 and a datum surface, such as mean sea level. 



2. The vertical angle between the plane of the 

 horizon and the line to the observed point, as a 

 star. 



3. See elevation. 

 (2) 



ambient — The environment surrounding a body 

 but undisturbed or unaffected by it. 



ambient noise — The noise produced in the sea by 

 marine animals, ship and industrial activity, ter- 

 restrial movements, precipitation, and other un- 

 derwater or surface activity outside the measur- 

 ing platform and detection equipment itself. 



ambient temperature — The temperature of the 

 mediiun surromiding an object. 



American Mediterranean — A name for the Car- 

 ibbean Sea and the Gulf of Mexico region. 



ammonia nitrogen — An intermediate product of 

 the nitrogen cycle of the sea which is present 

 where organic matter decomposes in quantity. 



amphidromic point — A no-tide or nodal point on 

 a chart of cotidal lines from which the cotidal 

 lines radiate. {See figure for cotidal chart.) 



amphidromic region — ^An area surrounding an 

 amphidromic point in which the cotidal lines 

 radiate from the no-tide point and progress 

 through all houre of the tide cycle. {See figure 

 for cotidal chart.) 



amphidromic system — See amphidromic region. 



amphipod — One of an order (Amphipoda) of 

 elongate and usually laterally compressed 

 crustaceans. The species live in a variety of 

 habitats from the parasitic state to the deep 

 pelagic. Some species are semipermanent 

 members of fouling communities. 



amphitrite — A large inflatable ship. Sixty-five 

 feet long, weighing 6 tons, it draws only 14 

 inches wlien fully loaded. It has been used as 

 a tender in sea-diving operations. 



