MILITARY OCEANOGRAPHY 



tached around an oceanographic wire and sent 

 down to actuate the tripping mechanism on 

 oceanographic devices such as Nansen bottles 

 and current meters after they have been 

 lowered to the desired depth. 



metamorphic rock — Kocks which have undergone 

 structural and mineralogical changes, such as 

 recrystallization, in response to marked changes 

 of temperature, pressure, and chemical environ- 

 ment. (2) 



metaripples — See ripple marks. 



metasediments — See quick. 



meteor — A general term for any atmospheric 

 phenomenon including hydrometeors (such as 

 rain, cloud, fog, and mist) and lithometers 

 (atmospheric dust or salt particles) . The term 

 now is usually restricted to astronomical meteors 

 which are bodies travelling through interplan- 

 etary space whose remnants occasionally reach 

 the earth's surface as meteorites. 



meteorological tide — The change in water level 

 due to meteorological conditions, such as wind 

 and barometric pressure. (66) 



meter — The basic miit of length of the metric 

 system, equal to 1,650,763.73 wavelengths of Kr^ 

 orange-red radiation. On October 14, 1960 the 

 lltK General Conference on Weights and Meas- 

 ures adopted this standard to replace the plati- 

 num-irridium meter bar which had been kept 

 in Paris as the international standard of lengths 

 since 1889 under the Treaty of the Meter. 



2. A device for measuring, and usually indi- 

 cating, some quantity. ( 68 ) 



meter wheel — ^A special block used to support the 

 oceanographic wire payed out over the side of a 

 ship. Attached to or connected by means of a 

 speedometer cable is a gear box to measure the 

 length of wire. On some meter wheels the gear 

 box or counter is an integral part of the wheel. 



Metonic cycle — A period of approximately 19 

 years, during which all phase relationships be- 

 tween moon, sun, and earth occur. 



During any cycle, new and full moon will re- 

 cur on approximately the same day of the same 

 year. (68) 



microatoll — A circular growth of coral with a 

 central depression and a breadth of only a few 

 feet. (2} 



microcoquina — Partially cemented sand-size (2 

 millimeters and smaller) shell fragments. (2) 



microcurie — (abbreviated /j,c). One-millionth of 

 a curie ( 10"^ curie) . (41 ) 



micron — ( abbreviated fi). A unit of length equal 

 to one-millionth of a meter or one-thousandth 

 of a millimeter. The micron is a convenient 

 length unit for measuring wavelengths of in- 

 frared radiation, diameters of atmospheric par- 

 ticles, etc. (5) 



microplankton — Plankton within the size range 

 60 microns to 1 millimeter. Most phytoplank- 

 ton forms are included in this group and the 

 nannoplankton. 



microseism — A feeble oscillatory disturbance of 

 the earth's crust, detectable only by very sensi- 

 tive seismographs. 



Certain types of microseisms seem to be 

 closely correlated with atmospheric disturbances 

 and can be used to locate such disturbances, 

 especially in the case of tropical cyclones. In 

 addition, traffic, industrial activities, and wind 

 flexure of trees and tall structures can create 

 microseisms. (5) 



middle ground — Bar deposits formed by ebb and 

 flood tides in the middle of the channel at the 

 entrance and exit of a strait. They result from 

 the decrease in current velocity and deposition 

 of suspended material with the widening of the 

 channel at either end of the constriction. 



middle pack — See Baffin Bay pack. 



Middle Passage — The route across Melville Bugt 

 (made possible by the breaking up of the pack 

 ice in the center of Melville Bugt) which is a 

 direct course from Upernavik to Kap York, 

 Greenland. (21) 



mid-extreme tide — A level midway between the 

 extreme high water and extreme low water oc- 

 curring at a place, ^ee mean tide level. (68) 



Midocean Canyon — This term is not recom- 

 mended by the ACUF for an Atlantic Ocean 

 seachannel. 



midocean canyon — This term is not recommended 

 by the ACUF for a steep-walled, flat-floored 

 continuous depression up to 5 miles wide and 

 100 fathoms in relief that crosses a plain and 

 often leads into or out of a gap. See seachan- 

 nel. 



midoceanic islands — Isolated volcanic islands 

 rising from the deep sea floor, composed of 

 basaltic lava or limestone reefs on a base of vol- 

 canic rock. (2) 



midocean ridge — A great median arch or sea bot- 

 tom swell extending the length of an ocean basin 

 and roughly paralleling the continental mar- 

 gins. See Cordillera. (2) 



midocean rift — This term is not recommended 

 by the ACUF for a deep, narrow-notched, cleft 

 valley, or graben, which is reportedly found 

 almost continuously along the crest of a Cordil- 

 lera or ridge. See cordillera. 



midwater trawl — A bag-type net generally towed 

 laterally at dejDths ranging from just above the 

 bottom to the surface. Two types are : 



(1) Rigid — with a metal frame to form the 

 shape of the open end of bag. 



(2) Nonrigid — depends on floats, paravanes, 

 weights and/or depressors to form the shape of 

 the open end. 



migrating inlet — A tidal inlet, such as one con- 

 necting a coastal lagoon with the open sea, which 

 shifts its position in the direction of the long- 

 shore current flow. (2) 



military oceanography — The study of those spe- 

 cific characteristics and phenomena of the deep 

 sea environment which may influence the design 



105 



