OXYLUCIFERIN 



oscillation — The variation, usually with time, or 

 the magnitude of a quantity with respect to a 

 specified reference when the magnitude is alter- 

 nately greater and smaller than the reference. 

 (6) 



oscillation ripple — Tiny sediment waves with 

 sharp, narrow, symmetrical crests and broader, 

 more rounded troughs formed by the action of 

 currents of equal speed alternating in opposite 

 directions. (2) 



oscillatory wave — ^A wave in which each indi- 

 vidual particle oscillates about a point with little 

 or no permanent change in position. The term 

 is commonly applied to progressive oscillatory 

 waves in which only the form advances, the in- 

 dividual particles moving in closed orbits. Dis- 

 tinguished from a wave of translation. See 

 also orbit. (61) 



ostracod — One of a subclass (Ostracoda) of 

 minute crustaceans, the individuals of which 

 are unsegmented, laterally compressed, and en- 

 closed in a bivalve shell (carapace). Some 

 members are benthic; others are planktonic. 

 Many species are luminescent, and the dried 

 bodies of one genus often are used to demon- 

 strate bioluminescence. 



otolith — (or eaihone). An earbone of a fish or 

 marine mammal (such as a whale) . Such bones 

 are more resistant to decomposition, digestion, or 

 solution than other bones and frequently occur 

 in marine sediment samples. 



otter trawl — A large commercial fishing trawl 

 using kitelike wooden boards at the corners of 

 the mouth of the net. The boards are attached 

 to long cables and so angled that water pressure 

 drives them apart and keeps the net well spread 

 as it drags along the sea floor. (35) 



outcrop — (or exjyosure). Naturally protruding, 

 or erosionally exposed or uncovered part of a 

 rock, bed, or formation, most of which is covered 

 by overlying material. 



outer ridge — See ridge, rise. 



outer slope — The steeply descending outer slope 

 of the reef below the dwindle point of abmidant 

 living coral and coralline algae, which is or- 

 dinarily at about 10 fathoms. (56) {See fig- 

 ure for atoll.) 



outflow — 1. The flow of water from the river or its 

 estuary to the sea. 



2. Total volume for any given period of time. 



outlet glacier — A stream of ice from an ice cap 

 to the sea. (68) 



overfalls — Breaking waves caused by opposing 

 currents or by the wind moving against the 

 current. (73) 



overlapping mean — See consecutive mean. 



overtide — A shallow water harmonic tide con- 

 stituent with a speed that is a multiple of the 

 speed of one of the basic constituents of the tide- 

 producing force. (49) See shallow water 

 constituent. 



overtopping — The amount of water passing over 

 the top of a structure as a result of wave run-up 

 or surge action . (61) 



overturn — (also called convective overturn). 

 The renewal of bottom water that occurs an- 

 nually in lakes and ponds in regions wherever 

 winter temperatures are cold enough. As the 

 surface waters are cooled in the autumn and 

 early winter, they become denser and therefore 

 sink, until the whole body of water is at 4:°C, the 

 temperature of maximum density. Further 

 cooling is restricted to the surface layers, since 

 both ice and water colder than 4°C are less dense 

 than the underlying waters at 4°C. 



This phenomenon does not take place over 

 most areas in the ocean because of the salinity 

 stratification, and usually the resulting brine is 

 dense enough to sink to the bottom only in the 

 extreme polar regions, where extensive freezing 

 occurs. (5) 



overwash — That portion of the uprush that car- 

 ries over the crest of a berm or of a structure. 

 (61) 



own-ship's noise — (or self -rwise). Often the 

 limiting noise registered by a sonar receiver 

 produced by the ship (or equipment) itself or as 

 a result of its motion. (28) 



oxygen — The element occurring as a free gas in 

 the atmosphere and as a dissolved gas in sea 

 water, where it is usually measured in milliliter 

 per liter. The concentration of dissolved oxygen 

 in the sea generally at N.T.P. ranges between 

 and 8 milliliters per liter. Its saturation con- 

 centration decreases with increasing temperature 

 and salinity. 



The oxygen content of sea water generally de- 

 creases from a maximum at and near the surface 

 to a minimum between 500 and 1,500 meters 

 (1,640 and 4,921 feet) , then increases with depth. 



oxygen minimum layer — A subsurface layer in 

 which the dissolved oxygen content is very low 

 or nil. (25) 



oxygen technique — (or light and dark hottle tech- 

 nique). A method of measuring gross photo- 

 synthesis by following the changes in dissolved 

 oxygen in a water sample containing phyto- 

 plankton. The method involves the use of 

 light bottles for indicating net photosynthesis 

 (oxygen evolution) and the use of dark bottles 

 to indicate loss of oxygen due to respiration. 

 Gross photosynthesis then equals the amount of 

 oxygen gained in the light bottle plus the amount 

 of oxygen lost through respiration in the dark 

 bottle. 



oxyluciferin — An end product of oxidized lucif- 

 erin compounds. In a generalized reaction 

 oxyluciferin, water, and energy released as a 

 form of visible light are produced during a 

 chemiluminescent reaction involving a luciferin 

 compound and luciferase, a biological catalyst. 



117 



