SHELF SEAS 



sequence of current — The order in which the four 

 tidal current strengths occur dully, with special 

 reference as to whether the stronger flood im- 

 mediately precedes or follows the stronger ebb. 

 Usually associated with mixed tidal currents 

 having inequalities in speeds and durations. 



sequence of tide — The order in which the four 

 tides of a day occur, with special reference as to 

 whether the higher high water immediately 

 precedes or follows the lower low water. 

 Usually associated with a mixed tide having 

 inequalities in heights and durations. (50) 



sergestid — One of a family (Sergestidae) of 

 usually deep pelagic shrimps or prawns. 



serial station — (also called hydrographic sta- 

 tion). An oceanographic station consisting 

 of one or more Nansen oasts. ( 5 ) 



serpulid — See tubeworm. 



sessile — ^1. Attached directly by base, without 

 stipe or stalk. 



2. Permanently attached; not free to move 

 aibout. 



seston — The living and nonliving bodies which 

 swim or float in water. 



set — 1. (or current direction). The direction 

 toward which the current flows. Usually indi- 

 cated in degrees true or points of the compass. 



2. (or settle). To attach to a surface, as by 

 the larvae of various marine invertebrates. 



3. The periodic attachment of many larvae of 

 marine invertebrates, especially barnacles and 

 bivalves, to a surface. 



settle — See set. 



settling volume — The amount of plankton in a 

 container concentrated by gravity and having 

 variable quantities of interstitial water. 



shadow zone — A region into which" very little 

 sound energy penetrates. 



shallow marginal seas — See shelf seas. 



shallows — An indefinite term applied to expanses 

 of shoal or shallow water. 



shallow scattering layer — The population (s) of 

 organisms in water over a continential shelf 

 which scatter sound. The organisms usually oc- 

 cur as separate groups or patches and are dis- 

 continuous horizontally. The horizontal dimen- 

 sions of such patches on the echo-sounder record 

 usually are less than the vertical dimensions. 

 See deep scattering layer, surface scattering 

 layer. 



shallow water — (or very shallow ivater). 1. 

 Commonly, water of such a depth that surface 

 waves are noticeably affected by bottom topog- 

 raphy. It is customary to consider water of 

 depths less than half the surface wavelength as 

 shallow water. 



2. In hydrodynamics with regard to progres- 

 sive gravity waves, water in which the depth 

 is less than 1/25 the wavelength. 

 (61) 



shallow water constituent — A short-period har- 

 monic term introduced into the formula of ■as- 



tronomical tide constitutents to take account of 

 the change in the form of a tide wave resulting 

 from shallow water conditions. Shallow water 

 constituents include overtides and compound 

 tides. (50) 



shallow water wave— (also called very shallow 

 water wave). A progressive gravity wave 



which is in water less than 1/25 the wavelength 

 in depth. (73) 



shard — A curved, spiculelike fragment of vol- 

 canic glass. (2) 



shark — (or selacM-an) . Any of approximately 

 250 species of fishlike vertebrates belonging to 

 the elasmobranch order Selachii, and including 

 the large plankton-feeding basking whale and 

 sharks, the predacious white, mako, tiger, blue, 

 hanimerhead, sand, and gray sharks, and a 

 variety of others such as the cow, frill, horn, 

 thresher, nurse, cat, angel, and dogfish sharks. 



shear crack — A crack in sea ice caused by two dif- 

 ferent, simultaneous forces acting in parallel 

 but opposite directions on adjacent portions of 

 the ice. The sheared parts undergo a displace- 

 ment parallel to the plane of the crack. (68) 



shearing stress — Any of the tangential compo- 

 nents of the stress tensor. In oceanography, 

 the shearing stress exerted on the sea surface by 

 the wind. 



sheet flow — See laminar flow. 



sheet ice — Ice formed in a smooth thin layer on 

 a water surface by the coagulation of frazil or 

 sludge. (5) 



sheet-type luminescence — 1. A display of biolog- 

 ical light appearing diffuse or shimmering, 

 often making the sea surface appear milky or 

 greenish in color. This type of display usually 

 is caused by masses of microscopic or tiny or- 

 ganisms. Displays may cover large areas of the 

 sea surface, at times causing a uniform glow 

 from horizon to horizon, or they may appear as 

 irregular patches or wide ribbons of light in an 

 otherwise dark sea. See bioluminescence. 



2. Called "spilled luminescence" in Kussian 

 papers. 



shelf — 1. This term is not recommended by 

 ACUF for a rock ledge, reef, or sandbank in the 

 sea. 



2. Short form for continental (or island) 

 shelf. 



shelf break — See shelf edge. 



shelf edge — The line along which there is a 

 marked increase of slope at the outer margin of 

 a continental (or island) shelf. (62) 



Note: Conventionally the shelf edge has been 

 taken at 100 fathoms (200 meters). 



shelf ice — See ice shelf. 



shelf seas — (or sh-allow marginal seas) . Shallow 

 seas which occupy wide portions of a continen- 

 tal shelf. See also epeiric seas, inland seas, 

 epicontinental seas. 



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