AUTOMATIC TIDE GAGE 



automatic tide gage — An instrument that auto- 

 matically registers the rise and the fall of the 

 tide. (50) 



automatic weather station — A weather station at 

 which the services of an observer are not re- 

 quired. Most automatic weather stations are 

 equipped with telemeter apparatus for trans- 

 mitting weather information at predetermined 

 times, or by use of an interrogation system. 



autophytic nutrition — See autotrophic nutri- 

 tion. 



autotrophic nutrition — That process by which 

 an organism manufactures its own food from 

 inorganic compounds. See holophytic nutri- 

 tion, chemotrophic nutrition, heterotrophic 

 nutrition, mixotrophic nutrition. 



autumn ice — 1. Sea ice in early stage of forma- 

 tion. It is comparatively brackish, and crystal- 

 line in appearance. Like young ice, it is not 

 yet affected by lateral pressure. ( 5 ) 



2. A Russian term defining a specific form 

 of one-year ice (70 to 200 centimeters thick). 

 At the end of the growth season in spring the 

 thickest one-year ice is also called autumn ice 

 since it formed earliest the previous autunui. 

 Thus, it has been defined as 150 to 200 centi- 

 meters or more thick. Autumn ice usually does 

 not completely disappear during the summer. 



autumn maximum — A secondary flowering of 

 phytoplankton. The flowering results from the 

 regeneration of nutrients after the decomposi- 

 tion of organisms that have died during the 

 summer and from vertical mixing after summer 

 stratification. 



auxiliary thermometer — A mercury-in-glass 

 thermometer attached to the stem of a reversing 

 thermometer. It is read at the same time as the 

 reversing thermometer so that the correction to 

 the reading of the latter, resulting from change 



in temperature after reversal, can be computed. 



(^) . . 



average — See arithmetic mean. 



average current — See mean current. 



average depth — The average water depths based 

 on soundings reduced to low water datum. 



average limit of ice — Average seaward extent of 

 ice during a normal winter. 



avulsion — Rapid erosion of shoreland by waves 

 during a storm. ( 73 ) 



awash — 1. Tossed about or bathed by waves or 

 tide. (61) 



2. A rock exposed or one just bare at any stage 

 of the tide between the datum of mean high 

 water and the sounding. 



axis of acoustic symmetry — For many trans- 

 ducers the three-dimensional directivity is such 

 that it may be represented by the surface gen- 

 erated by rotating a two-dimensional directivity 

 pattern about the axis corresponding to the ref- 

 erence bearing of the transducer. This axis may 

 then be described as an axis of acoustic sym- 

 metry, or, more briefly, as the acoustic axis. 

 (28) 



axis of channel — The center line of a channel. 

 (30) 



azoic — ^Without life; however, most ocean areas 

 described as azoic are known to contain at least 

 a bacterial flora. 



Azores high — The semipermanent subtropical 

 high over the North Atlantic Ocean, so named 

 especially when it is located over the eastern part 

 of the ocean. 



The same high, when displaced to the western 

 part of the Atlantic, or when it develops a sepa- 

 rate cell there, is known as the Bermuda high. 

 On mean charts of sea-level pressure, this high is 

 one of the principal centers of action in north- 

 ern latitudes. (5) 



14 



