SLIGHTLY STRATIFIED ESTUARY 



silicate silicon — Ionic form of silicon utilized by 

 various plankters, principally diatoms and 

 radiolarians. The measurement of silicates in 

 sea water is useful for determining diatom 

 productivity. 



siliceous ooze — A fine-grained pelagic sediment 

 containing more than 30 percent siliceous skel- 

 etal remains of pelagic plants and animals. 



silicoflagellate — Any of a group of microscopic 

 marine phytoplankton having siliceous shells 

 with radiating spines; they are inhabitants 

 principally of colder waters. 



sill — The low part of the ridge or rise separating 

 ocean basins from one another or from the 

 adjacent sea floor. (62) 



sill depth — The greatest depth over a sill. (62) 



sill basin — (or harred has'in) . A submarine basin 

 separated from the main basin by a narrow sub- 

 merged ridge. Deep water in the silled basin 

 may be stagnant and anaerobic. An example 

 is Fossa de Cariaco, Venezuela. ( 2 ) 



silt — An unconsolidated sediment whose particles 

 range in size from 0.0039 to 0.0625 millimeter 

 in diameter (between clay and sand sizes) . See 

 phi grade scale. 



simple harmonic wave — An oscillation translat- 

 ing with constant speed and amplitude, and rep- 

 resented mathematically by a trigonometric or 

 complex exponential function. Thus, 



A sin ( --^ X— 1'^+^) or e exp * (t- X—vt+<pj 



represents a simple harmonic wave of amplitude 

 A, wavelength A, frequency v, and phase angle (p. 



In ocean wave studies, a simple harmonic 

 progressive wave is an idealized wave charac- 

 terized by constant speed of propagation and a 

 straight crest of indefinite length. (5) 



simple sound source — A source that radiates 

 sound uniformly in all directions under free- 

 field conditions. (6) 



single day tide — British terminology for diurnal 

 tide. (68) 



sinking — 1. (or dowmoelUng) . A downward 

 movement of surface water generally caused by 

 converging currents or when a water mass be- 

 comes more dense than the surrounding water. 

 See upwelling. 



2. In atmospheric optics, a refraction phe- 

 nomenon, the opposite of looming, in which an 

 object on or slightly above the geographic hori- 

 zon apparently sinks below it. Sinking occurs 

 whenever the rate of density with height 

 through the atmosphere is of smaller magnitude 

 than normal or, in extreme cases, where the 

 density actually increases with height. (5) 



siphonophore — One of an order (Siphonophora) 

 of medusoid coelenterates. Many are lumi- 

 nescent, some are venomous, and some posses a 

 pneumatophore (an air-filled float), which im- 

 parts a sound scattering capacity to the orga- 



nisms. A pneumatophore-bearing species has 

 been observed within the deep scattering layer. 



sirenian — See sea cow. 



size of floating ice — The linear extent of individ- 

 ual fragments of ice. In general, ice fragments 

 are angular or circular. The linear dimension 

 used for describing the size of an individual ice 

 fragment is an approximation of the diameter. 

 Size is usually observed either in feet and miles 

 or meters and kilometers, whichever is more 

 convenient or applicable. The terms most gen- 

 erally used to describe ice fragments accord- 

 ing to increasing size are in order: brash ice, 

 block, small ice floe, medium ice floe, giant 

 floe, and ice field. (65) 



skate barrow — See sailor's purse. 



skerries — Low, small islands, reefs, and rocks 

 which form a broad belt (skjsergard) extending 

 along a coast for hundreds of miles. Skerries 

 rise from a shallow coastal strandflat. 



skin — The first film or crust of newly formed 

 ice, with some degree of hardness. (68) 



skin diving — Free diving with or without 

 SCUBA gear. 



skjaergard — See skerries. 



sky map — A pattern on the underside of extensive 

 cloud areas created by the varying amounts of 

 light reflected from the earth's surface. Snow 

 surfaces produce 'a white glare in the sky (snow 

 blink) and ice surfaces a yellowish-white glare 

 (ice blink). Bare land and water surfaces re- 

 flect little or no light and for this reason the 

 clouds above these surfaces are relatively dark 

 (land sky, water sky). Generally the same 

 conditions can be observed from an aircraft 

 above the clouds, when the thickness of the cloud 

 layer permits. (65) 



slack ice — ^S'^'e broken ice. 



slack tide — See slack water. 



slack water — (sometimes called slach tide) . The 

 interval when the speed of the tidal current is 

 very weak or zero; usually refers to the period 

 of reversal between ebb and flood currents. In 

 some places slack water occurs near times of 

 high and low water, whereas in other localities 

 the slack water may occur midway between high 

 and low water. ( See figure for current curve. ) 



slant path velocity — The mean velocity along one 

 cycle of a sound ray path. 



slant range — The diagonal distance between a 

 point at one position and a point at another 

 position in a vertical plane. 



slat-flecked ice — Ice swept clear of snow except 

 for wind ripples saturated with brine. (59) 



slewing — In ice navigation, the act of forcing a 

 ship through ice by pushing apart adjoining ice 

 floes. (59) 



slide — See slump. 



slightly stratified estuary — An estuary in which 

 the salinity increases slightly with depth and 

 also increases noticeably along its length from 

 the head to the mouth. 



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