MY8TICETE 



monitoring — Periodic or continuous determina- 

 tion of the amount of ionizing radiation or 

 radioactive contamination present in an occu- 

 pied region as a safety measure for purposes of 

 health protection. (70) 



monsoon — A name for seasonal winds (derived 

 from Arabic "mausim," a season). It was first 

 applied to the winds over the Arabian Sea, 

 which flow for six months from nortlieast and 

 for six months from southwest, but it lias been 

 extended to similar winds in other parts of the 

 world. (5) 



monsoon current — A seasonal wind-driven cur- 

 rent occurring in the northern part of the In- 

 dian Ocean and the northwest Pacific Ocean. 



montmorillonite — A group of clay minerals char- 

 acterized by swelling in water. 



moraine — Rock debris, deposited chiefly by direct 

 glacial action, and having various constructional 

 topographic features independent of control by 

 the underlying preglacial surface. Where 

 glaciers float upon or discharge into the sea, 

 or glaciated regions are drowned by the sea, 

 moraines form marine deposits. 



moraine bar — A bar, rising from deep water on 

 both sides, which is composed of glacial detritus 

 including large boulders. It is deposited as a 

 terminal moraine by a valley glacier and extends 

 across a fiord. 



moss animal — See bryozoan. 



mouth — The place of discharge of a stream into 

 the ocean or entrance to a bay from the ocean. 



moving average — See consecutive mean. 



Mozambique Current — The part of the South 

 Equatorial Current that turns and flows along 

 the African coast in the Mozambique Channel. 

 It is considered part of the Agulhas Current, 



M2 constituent — The principal lunar semi- 

 diurnal constituent of the theoretical tide-pro- 

 ducing forces. {See figure for partial tide.) 



mud — Pelagic or terrigenous detrital material 

 consisting mostly of silt and clay-sized particles 

 (less than 0.06 millimeter) but often containing 

 varying amounts of sand and/or organic mate- 

 rials. It is a general term applied to any sticky 

 fine-grained sediment whose exact size classifi- 

 cation has not been determined. 



muddy ice — See debris ice. 



mud flat — A muddy or sandy coastal strip usually 

 submerged by high tide. ( 2 ) 



mud flow — See turbidity current. 



mud lumps — Small transient sigmoidal islands of 

 bluish-gray clay squeezed up by the pressure of 

 surface sediments or buried clays off the Missis- 

 sippi River delta. They rise to 5 or 10 feet 

 above sea level and are an acre or more in extent. 



mudstone — A rock consisting of an indefinite mix- 

 ture of clay, silt, and sand particles, the propor- 



tions varying from place to place. May also be 

 applied to shales. See pelite. 



mud volcano — (or hervidero). A cone-shaped 

 clay mound composed of clay and usually 

 formed by the eruption of sulfurous and bitumi- 

 nous mud from a central orifice or vent. There 

 are both land and submarine forms. 



mu (/x) flagellates — (or hekistoflankton) . The 

 extremely tiny phytoplankters measured in mi- 

 crons and bearing one or more whiplike hairs 

 (flagella). 



multichannel analyzer — See pulse height ana- 

 lyzer. 



multipath transmission — The process, or condi- 

 tion, in which radiation travels between source 

 and receiver via more than one path. Since 

 there can be only one "direct" path, some process 

 of reflection, refraction, or scattering must be 

 involved. ( 5 ) 



multiple tide staff — A succession of tide staffs 

 placed on a sloping shore, so that the vertical 

 graduations on the several staffs from a contin- 

 uous scale with reference to the same datum. 

 (68) 



mush — Rare. See brash ice. 



mushroom ice — See ice pedestal. 



mussel — One of a family (Mytilidae) of elongate, 

 tajaering bivalves, usually dark colored, grow- 

 ing in masses on stationary and floating objects, 

 underwater structures, rocks and rocky cliffs, or 

 ships' hulls, covering mud flats in the intertidal 

 zone, and boring into rock. Mussels attach by 

 means of a mass of threads called the byssus. 

 They are one of the most notable groups of foul- 

 ing organisms. 



mutualism — A symbiotic relationship between 

 two species in which both are benefitted. An 

 example of mutualism is the attachment of cer- 

 tain sponges and coelenterates to the shells of 

 crabs. The attached animal is carried about to 

 fresh feeding areas, and the crab is camouflaged 

 by the animal on its back and may be thus pro- 

 tected from enemies. See commensalism, in- 

 quilinism, symbiosis. 



myctophid — (or lanteim,f.slx) . One of a family 

 (Myctophidae) of small oceanic fishes which 

 normally live at depths between about 100 and 

 2,000 fathoms (200 and 4,000 meters). They 

 characteristically have numerous small photo- 

 phores on the sides of the body. Many species 

 undergo extensive diurnal vertical migrations 

 and are thought to contribute to sound scattering 

 layers in the sea. 



mysid — One of an order (Mysidacea) of elongate 

 crustaceans which usually are transparent (or 

 nearly so) and benthic or deep living. 



mysticete — See baleen whale. 



207-109 0—66 S 



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