BOTTOM ICE 



water against the bottom of the ocean, causmg 

 the waves to decrease in height. 



bottom ice — See anchor ice. 



bottom load — See load. 



bottom materials — See bottom sediments. 



bottom pressure — The pressure at a point on the 

 bottom of a body of water due to the weight of 

 the column of water above it. 



bottom pressure fluctuation — The change in 

 pressure at a point on the bottom of a body of 

 water as a surface wave passes over it. 



bottom reflection — The return of transmitted 

 sound from the bottom of the ocean. The char- 

 acteristics of reflected sound depend on the na- 

 ture of the bottom and on the wavelength of 

 the sound. 



bottom resistivity — The resistance, in ohms, be- 

 tween opposite faces of a unit cube of sediment. 

 It is governed more by the electrolyte concen- 

 tration of the liquid filling the interstices than 

 by the intrusive conductivity of the sediment 

 grains itself. 



bottom reverberation — See reverberation. 



bottom sample — A portion of the material form- 

 ing the bottom, brought up for inspection. 

 (68) 



bottom sampler — Any instrument used to obtain 

 a bottom sample. See grab. 



bottom sediments — (also called hottom ma- 

 teri-als). In general all sedimentary material 

 regardless of origin found on or in the subma- 

 rine bottom, including ballast or other material 

 dumped into the sea by man. More specifically 

 it is limited to unconsolidated mineral and or- 

 ganic material forming the sea bottom, not in- 

 cluding coral reefs or bedrock. 



bottom-set beds — The layers of fine alluvial sedi- 

 ments carried out and deposited on the bottom 

 of the sea in front of a delta. (2) 



BOTTOM-SET BEDS 



1. Top-set beds; 2. Fore-set beds; 3. Water surface; 4, Bottom- 

 set beds (AFICRi LEET. l. DON a JUDSON. SHELDON PHYSICAL 



GEOLOGY. NEW YOM PPENTfCE-HALL. (NC I9S. p 139) 



bottom temperature — Temperature observed at 

 the bottom of the sea. 



bottom water — The water mass at the deepest part 

 of the water column. It is the densest water 

 that is permitted to occupy that position by the 

 regional topography. See water mass. 



Bouguer anomaly — A difference between an ob- 

 served ^'alue of gravity and a theoretical value 

 at the point of observation, which has been cor- 

 rected for the effect of topography only, the to- 



pography being considered as resting on a plane 

 of indefinite extent. (37) 



Bouguer correction — A correction made in ob- 

 served gravity values for the altitude (eleva- 

 tion) above sea level of the station and tlie rock 

 betAveen the station and sea level. 



boulder — (or howlder). A rounded rock with a 

 diameter of 256 millimeters or larger. See phi 

 grade scale. 



boulder barricade — A coast bordered with lines 

 of innumerable large boulders visible between 

 low water and half tide. 



boulder clay— Unstratified or little stratified and 

 unsorted deposit of silty and clayey materials in 

 which are embedded particles of sand to boul- 

 der size. (2) 



boulderet — See cobble. 



boulder gravel — Deposit of uncemented boul- 

 ders. (2) 



boundary layer — A term referring broadly to 

 the layer of fluid in the immediate vicinity of 

 a bounding" surface. It is the layer in which 

 frictional forces are not negligible. 



boundary surface — See interface. 



Bourdon tube — Part of the temperature sensing 

 element in a bathythermograph. It consists 

 of a hollow brass coil connected to a xylene 

 filled tube, with one end fixed and the other free 

 to move with temperature expansion and con- 

 traction. 



bowlder — See boulder. 



box gage — (or float gage). A tide gage that is 

 operated by a float in a long, vertical stationary 

 box to which the tide is admitted through an 

 opening in the bottom. (50) 



brachial — Pertaining to armlike structures, such 

 as to the rays of starfishes. 



brachiolaria — A more advanced stage of the bi- 

 pinnaria larva of a sea star. 



brachiopod — (or lam.p shell). One of a phylum 

 (Brachiopoda) of sessile, marine, mollusklike 

 animals in which the body, whose construction 

 differs considerably from that of the mollusks, 

 is enclosed in calcareous or horny bivalve shell. 

 Most species live in shallow water. Many fossil 

 species are known. 



brackish water — Water in which salinity values 

 range from approximately 0.50 to 17.00 parts 

 per thousand. (35) 



branch fiord — A bifurcation of a narrow deep 

 arm of the sea. 



branchial — Pertaining to gills. 



branching bay — See estuary, 



brash ice 



than 2 meters (6.6 feet) in diameter. (74) 



brave west winds — A nautical term for the strong 

 and rather persistent westerly winds over the 

 oceans in temperate latitudes. 



They occur between 40° and 65°N in the 

 Northern Hemisphere and 35° to 65°S in the 

 Southern Hemisphere, where they are more 

 regular and are strongest between 40° and 50°S 



A fragment of sea ice or river ice less 



24 



