BOTTOM FRICTION 



block — 1. A sea ice fragment more than 6 feet but 

 less tlian 30 feet in diameter. See ice cake. 



(59) 



Note : The WMO is attempting to phase out 

 this term. 



2. An angular rock fragment variously de- 

 fined as being larger than 4 millimeters, larger 

 than 3-2 millimeters, or larger than 256 milli- 

 meters. (2) 



blocky iceberg — An iceberg with steep, precipi- 

 tous sides, and with an essentially horizontal 

 u)5per surf ace. (68) 



bloom — See plankton bloom. 



blowing spray — Spray lifted from the sea surface 

 by the wind and blown about in such quantities 

 that the horizontal visibility is restricted. (5) 



blown sands — See eolian sands. 



blue-green alga — One of a division or phylum 

 (Cyanophyta) (the Myxophyceae of another 

 scheme) of single-celled or simply filamentous 

 plants in which the blue color is imparted by a 

 water-soluble accessory pigment, c-phycocyanin. 

 In the ijlanktonic form, SJcujaella (Trichodes- 

 mium) erythraea, for whose color the Red Sea 

 was named, a red pigment dominates the others. 

 Attached forms have a characteristic scummy or 

 velvety growth on boat bottoms, rocks, and other 

 underwater surfaces. Large masses of plank- 

 tonic forms cause "sliming'' of the water. 



blue ice — The oldest and hardest form of glacier 

 ice. It is distinguished by a slightly bluish or 

 greenish color. (65) 



blue mud — A combination of terrigenous and deep 

 sea sediments having a bluish gray color due to 

 the presence of organic matter and finely divided 

 iron sulfides. Calcium carbonate is present in 

 variable amounts up to 35 percent. 



bluff — A headland or cliff with a bold almost per- 

 pendicular front. 



boat channel — A shallow, narrow channel on a 

 reef flat which separates a fringing reef from 

 the shore. It is parallel to shore and generally 

 only a few feet deep. 



body waves — Either transverse or longitudinal 

 seismic waves transmitted in the interior of an 

 elastic solid or fluid, and not related to a bound- 

 ary surface. (35) 



boiling point — The temperature at which the 

 equilibrium vapor pressure between a liquid and 

 its vapor is equal to the external pressure on the 

 liquid. 



The boiling point of pure water at standard 

 atmospheric pressure is equal to 100°C (212°F) 

 and is a fiducial point for thennometer calibra- 

 tion. (5) 



bold coast — ^A prominent landmass that rises 

 steeply from the sea. ( 61 ) 



bolometer — An instrument for measuring ther- 

 mal radiation. (68) 



bora — A fall wind whose source is so cold that 

 when the air reaches the lowlands or coast the 

 dynamic warming is insufficient to raise the air 



temperature to the normal level for the region; 

 hence it api)ears as a cold wind. 



The term was originally and still is applied 

 to the cold northeast wind on the Dalmatian 

 coast of Yugoslavia in winter when cold air from 

 Russia crosses the mountains and descends to the 

 relatively warm coast of the Atlantic. It is 

 very stormy and squally, the squalls sometimes 

 reaching 100 miles per hour or more. (5) 



borderland — A not so commonly used term for the 

 declivity which marks the inner or landward 

 margin of the continental borderland; the 

 ACUF did not find sufficient evidence of this 

 type of feature to warrant inclusion in their rec- 

 ommended terms and definitions. 



borderland slope — The declivity which marks the 

 inner or landward margin of the continental 

 borderland. (2) 



bore — 1. See hydraulic jump. 



2. (also called eager, rimscaret, or tidal hore). 

 A. high breaking wa^-e of water, advancing 

 rapidly up an estuary. Bores can occur at the 

 mouths of shallow rivers if the tide range at the 

 mouth is large. They can also be generated in 

 a river when tsunamis enter shallow coastal 

 water and propagate up the river. ( 5 ) 



3. A submarine sand ridge in very shallow 

 water. It may build up to intertidal level. (2) 



4. See borehole. 



borehole — (or horing, hore). A hole drilled into 

 the earth to obtaiii samples of and measure the 

 physical properties of the rock and sediments 

 penetrated. 



borer — See marine borer. 



boring — 1. Forcing a ship under power through 

 ice, by breaking a lead. 



2. xS'ee borehole. 

 (68) 



bottle paper — See drift bottle. 



bottle post — See drift bottle. 



bottom — Any ground covered by water. Bed 

 refers nlore specifically to the whole submerged 

 basin, and floor is the essentially horizontal sur- 

 face of the gromid beneath the water. 



bottom bounce — A technique by which acoustic 

 energy is reflected oft' the ocean bottom one or 

 more times before reaching the target. 



bottom flow — (or vnderfloio) . A current denser 

 than any part of the surrounding fluid and 

 which flows along the sea bottom. 



bottom friction — The force resulting from the in- 

 teraction between the ocean bottom and water 

 particle motion over it. In the case of currents, 

 it is a retarding force acting in a direction op- 

 posite to the current flow. It is proportional to 

 the roughness of the bottom, water density, ve- 

 locity of the current, and water depth. The ef- 

 fect of bottom friction is also of importance in 

 forecasting waves in shallow water. As the 

 waves travel over shallow water they lose con- 

 siderable energy because of the stress of moving 



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