ORTHOGONAL 



O, constituent — The lunar diurnal constituent 



of the theoretical tide-producing forces. {See 

 figure for partial tide.) 



ooze — 1. A soft mud or slime. 



2. A fine-grained pelagic sediment containing 

 undissolved sand- or silt-sized, calcareous or sili- 

 ceous skeletal remains of small marine organisms 

 in proportion of 30 percent or more, the re- 

 mainder being amorphous clay-sized material. 

 Deep sea oozes often are characterized by mark- 

 edly bi-modal grain-size distributions, one mode 

 being in the sand or silt range, the other in the 

 clay range. See also diatomaceous, formi- 

 niferal, globigerina, pteropod, and radio- 

 larian oozes. 



open drift ice — See open pack ice. 



open ice — See broken ice. 



open ice edge — Unsteady and not sharply defined 

 ice edge limiting an area of open ice, usually 

 located to the leeward. (74) 



opening — Any break in sea ice which reveals the 

 water. 



open lead — A lead that is not covered with ice. 

 (68) 



open ocean — See oceanic. 



open pack ice — (or open drift ice). Ice floes of 

 sea ice that are seldom in contact with each 

 other; generally covering between 4- and 6- 

 tenths (or 3- to 5-eighths) of the sea surface. 

 (74) 



open port — A port which is not icebound during 

 winter. 



open sound — A bay similar to a lagoon but with 

 large openings between the protecting islands. 

 (2) 



open water — 1. A relatively large area of free 

 navigable water in an ice filled region. (68) 



2. More specifically, water which has less than 

 one-tenth of its surface covered with floating 

 ice. (59) 



operculum — (or gill cover). In fishes, a bony or 

 membranous flap covering the external openings 

 of the gill slits. 



ophiopluteus — The planktonic larva of a brittle 

 star. 



opposing wind — Generally, same as headwind; 

 specifically, a wind blowing in the direction 

 opposite to ocean-wave advance ; the opposite of 

 following wind. (5) See crosswind. 



opposition — The situation of two celestial bodies 

 with their celestial longitudes (the angular dis- 

 tance measured east of the vernal equinox along 

 the ecliptic) differing by 180 degrees; for exam- 

 ple, opposition occurs when the moon and the 

 sun are directly in line with the earth and on 

 opposite sides of the earth. (66) {See figure 

 for tide cycle.) 



optical filter — A device which changes, by absorp- 

 tion or interference, the magnitude or the spec- 

 tral distribution of the radiant energy passing 

 through it. (8) 



optical length — ^The geometrical length of a path 

 multiplied with the total attenuation coefficient 

 associated with the path. (8) 



optimum ship routing — A technique for routing 

 ships, based on knowledge of sea currents, 

 weather, and wave conditions to get a ship to 

 its destination in the quickest time and with 

 least damage to cargo or discomfort to passen- 

 gers. 



orange peel sampler — A bottom sediment sam- 

 pling device capable of obtaining as much as 

 14 cubic foot of sample from the ocean floor. 

 Named for its likeness to an orange that has its 

 peel quartered. 



orbit — In water waves, the path of a water particle 

 affected by the wave motion. In deepwater 

 waves the orbit is nearly circular, and in shal- 

 low water waves the orbit is nearly elliptical. 

 In general, the orbits are slightly open in di- 

 rection of wave motion, giving rise to mass 

 transport. (61) /See figure on next page. 



orbital current — The flow of water accompany- 

 ing the orbital movement of the water particles 

 in a wave. Not to be confused with wave-gen- 

 erated littoral currents. (6) See mass trans- 

 port. 



orbital energy — The total energy associated with 

 the oAital motion of all water particles. 



orbital energy difference — The excess of orbital 

 energy of water particles in orbital motion at 

 any depth over that at any lower depth of the 

 same water column. 



orbital motion — See orbit. 



orbital period — The time required for a water 

 particle in orbital amotion to complete one or- 

 bit. 



orbital speed — The speed of water particles in 

 orbital motion along their orbits. 



order — See classification of organisms. 



ordinary tide level — See mean tide level. 



ordinary tides — ^The word "ordinary" may be 

 used in tides as the equivalent of the word 

 "mean." (50) 



organic bank — See organic reef. 



organic reef — A sedimentary rock aggregate com- 

 posed of living and dead colonial organisms 

 such as algae, coral, cnnoids, and bryozoa. 

 Wlien it is covered by more than 6 fathoms of 

 water, it is an organic bank. 



orogeny — Large scale regional mountain form- 

 ing processes by folding, faulting, and thrust- 

 ing. 



orthogonal — (or wave ray). A member of a 

 family of curves everywhere perpendicular to 

 the family of curves representing wave crests 

 on a refraction diagram; analogous to rays in 

 the theory of geometrical optics. (73) {See 

 figure for refraction diagram.) 



U5 



