o 



oarweed — The British term for a blade-shaped 



brown alga. See kelp, 

 oblique haul — ( or oblique tow ) . The retrieval of 



an open plankton net from a certain depth at a 



certain rate while the ship is underway. See 



horizontal haul, vertical haul, 

 oblique tow — See oblique haul, 

 observed depth — See accepted depth, 

 observed gravity — The uncorrected value ofgrav- 



ity at a station as determined from the gravity 



meter. 

 ocean — (or sea). 1. The intercommunicating 



body of salt water occupying the depressions of 



the earth's surface. 



2. One of the major primary subdivisions of 



the above, bounded by continents, the Equator, 



and other imaginary lines. 



(5) 



ocean basin — That part of the floor of the ocean 

 that is more than about 100 fathoms below sea 

 level. (2) 



ocean current — A movement of ocean water char- 

 acterized by regularity, either of a cyclic nature 

 or more commonly as a continuous stream flow- 

 ing along a definable path. 



Three general classes, by cause, may be dis- 

 tinguished: (1) currents related to sea water 

 density gradients, comprising the various types 

 of gradient currents; (2) wind-driven cur- 

 rents, which are those directly produced by the 

 stress exerted by the wind upon the surface and ; 

 (3) currents produced by long-wave motions. 

 Tlie last is principally the tidal currents, but 

 may include currents associated with internal 

 waves, tsunamis, and seiches. The major 

 ocean currents are of continuous, stream-flow 

 character, and are of first-order importance in 

 the maintenance of the earth's thermodynamic 

 balance. (5) 



oceanic — (or high seas., open ocean). That por- 

 tion of the pelagic division seaward from the 

 approximate edge of a continental shelf. {See 

 figure for classification of marine environ- 

 ments.) 



oceanic anticyclone — See subtropical high. 



oceanic climate — See marine climate. 



oceanic crust — A mass of gabbroic mat«rial ap- 

 proximately 5-kilometers thick which lies under 

 the ocean bottom and may be more or less con- 

 tinuous beneath the continental crust. (35) 



oceanic high — See subtropical high. 



oceanicity — (or oceanity). The degree to which 

 a point on the earth's surface is in all respects 

 subject to the influence of the sea; the opposite 

 of continentaiity. Oceanicity usualh' refers to 

 climate and its effects. One measure for this 

 characteristic is the ratio of the frequencies of 

 maritime to continental types of air masses. 



(5) 



oceanic polar front — See Antarctic Conver- 

 gence, Arctic Convergence. 



oceanic province — See pelagic division. 



oceanity — See oceanicity. 



oceanogenic sedimentation — Sediments exclu- 

 sively marine, siliceous, chemical, or organic in 

 origin which accumulate in abyssal depths far 

 from land. 



oceanographic cast — A single lowering of a series 

 of Nansen bottles at an oceanographic station. 



oceanographic analysis — The science of manual 

 or automatic production of charts of oceano- 

 graphic parameters in which isopleths are 

 drawn to indicated data by some rational theory. 



oceanographic equator — (or thermal equator). 

 The zone of maximum sea surface temperature 

 located near the geographic equator. It gen- 

 erally lies north of this line ; but crosses during 

 the southern summer in the Indian Ocean, west- 

 ern Pacific Ocean, and western Atlantic Ocean> 

 Some oceanographers define the oceanographic 

 equator more specifically as the zone within 

 which the sea surface temperature exceeds 28 °C 

 (82.4°F). 



oceanographic forecasting — The production by 

 automatic or manual means of charts showing 

 forecasted values of oceanographic parameters, 

 similar to weather charts. 



oceanographic model — A theoretical representa- 

 tion of the marine environment. Generally, a 

 pattern or expression which relates known with 

 derived oceanographic properties. These ocean- 

 ographic properties may be physical, chemical, 

 geological, and/or biological. 



oceanographic slide rule — A specially designed 

 slide rule used for calculating the correction of 

 thermal expansion of a deep sea reversing 

 thermometer. 



oceanographic station — A term used to designate 

 oceanographic observations taken at a geo- 

 graphic location from a ship that is lying to or 

 anchored at sea. 



113 



