BIOSPHERE 



ter per unit of water surface or volume ex- 

 pressed in weight units. 



biosphere — Tliat transition zone between earth 

 and atmospliere witliin which most forms of ter- 

 restrial life are commonly found ; the outer por- 

 tion of the geosphere and inner or lower portion 

 of the atmosphere. 



biostromal limestone — See coquina. 



biostrome — Bedded structures such as shell beds 

 consisting of and built mainly by sedentary or- 

 ganisms ; not a moundlike or lenslike form. See 

 also accretionary limestone, bioherm, reef. 



.(2) 

 biota — The fauna and flora of a given region. 



. (5.8) 

 biotic factors — Factors of a biological nature, 



such as availability of food, comijetition be- 

 tween species, predator-prey relationships, etc., 

 which, besides the purely phj^sical and chemical 

 factors, also affect the distribution and abun- 

 dance of a given species of plant or animal. 

 (25) 



biotic succession — The natural replacement of 

 one or more groups of marine organisms grow- 

 ing in a specific habitat by other groups, the 

 preceding groups in some way preparmg or 

 favorably modifying the habitat for the suc- 

 ceeding groups. 



bipinnaria larva — The usually planktonic young 

 of a sea star. 



Birch discontinuity — Seismic discontinuity 

 within the earth's mantle at a depth of about 

 900 kilometers (about 558 statute miles), pos- 

 sibly caused by a chemical or phase change, or 

 both. (2) 



bird-foot delta — A delta formed by the out- 

 growth of pairs of natural levees making the 

 digitate or bird-foot form. 







T^i^S^ 





BIRD-FOOT DELTA 



(AFTIH: LOBEOC, A.K., -GEOMORPHOLOGY AN 

 NTRODUaiON TO THE SlUOr Of lANDSCAPING. ' ' 

 NEW YORK: McGRAW-HIU. 1939. p 230.) 



bit — 1. A small piece of sea ice; a single fragment 

 of brash ice. 



2. A binary unit of information. (5) 



bittern — The liquid remaining after sea water has 

 been concentrated by evaporation until salt has 

 crystallized. (5) 



bivalve — (or -pelecypod, lamellibranch) . One of 

 a class (Pelecypoda or lamellibranch) of mol- 

 lusks generally sessile or burrowing into soft 

 sediment, rock, wood, or other materials. In- 

 dividuals possess a hinged shell and a hatchet- 

 shaped foot, which in some is used in digging. 

 The clams, oysters, and mussels belong to this 

 class; many of the latter two mollusks are no- 

 table fouling organisms; several are marine 

 borers. 



black and white iceberg — An iceberg having a 

 dark, opaque portion containing sand and 

 stones, and separated from the white portion by 

 a definite line of demarcation. (68) 



black body radiation — The electromagnetic ra- 

 diation emitted by an ideal black body ; it is the 

 theoretical maximum amount of radiant energy 

 of all wavelengths which can be emitted by a 

 body at a given temperature. ( 5 ) 



black bottle — (also called dark bottle). A con- 

 tainer used in measuring respiratory activity of 

 primary producers. The container is covered 

 or coated to exclude light and thereby prevent 

 photosynthetic activity. See light bottle. 



black fish — See pilot whale. 



black ice — Thin, new ice on fresh or salt water, 

 appearing dark in color because of its trans- 

 parency. (59) 



black mud — (also called hydrogen sulfide mud). 

 A dark fine-grained sediment formed in poorly 

 aerated bays, lagoons, and fiords. This sedi- 

 ment contains large quantities of decaying or- 

 ganic matter and iron sulfides and generally 

 exudes hydrogen sulfide gas. 



blade — The expanded or elongate leaflike part of 

 the larger algae, especially kelp. See lamina. 



blanket deposit — A sedimentary deposit of uni- 

 form thickness which covers a wide region. 



blast wave — A sharply defined wave of increased 

 pressure rapidly propagated through a sur- 

 rounding medium from a center of detonation 

 or similar disturbance. (63) 



blind lead — (also called cul-de-sac, pocket). A 

 lead with only one outlet. ( 68 ) 



blind rollers — Long, high swells which have in- 

 creased in height, almost to the breaking point, 

 as they pass over shoals or run in shoaling 

 water. (61) 



blink — See ice blink, snow blink. 



blizzard — A severe weather condition character- 

 ized by low temperatures and by strong winds 

 bearing a great amount of snow (mostly fine, 

 dry snow picked up from the ground). The 

 U.S. Weather Bureau specifies for blizzard, a 

 wind of 28 knots or higher, low temperatures, 

 and sufficient snow in the air to reduce visibility 

 to less than 500 feet. ( 5 ) 



22 



