CHIP LOG 



centrosphere — (also called hari/f!phere, core). 

 The central core of the eartli, composed of dense 

 material, and making up most of its mass. (2) 

 {See fio-ure for earth structure.) 



cephalopod — One of a class (Cephalopoda) of 

 benthic or free-swimmino; mollusks possessing 

 a large head, large eyes, and a circle of arms or 

 tentacles around the mouth; the shell is external, 

 internal, or absent, and an ink sac usually is 

 present. See squid, octopus, nautilus. 



cetacean — A marine mammal of the order Ce- 

 tacea, wliich includes the whales, dolphins, and 

 porpoises. 



cgs system — The system of physical measure- 

 ments in which the fundamental units of length, 

 mass, and time are the centimeter, gram, and 

 second, respectively. (37) 



chaetognath — See arrow worm. 



chain bag dredge — See chain mesh dredge. 



chain mesh dredge — (also called chain hag 

 dredge). A bottom sampler constructed of a 

 rectangular steel collar attached to a chain mail 

 purse lined with screens or netting. It is used 

 on the continental shelf to collect coarse-grained 

 sediments and bottom dwelling organisms. 



chain reaction — Any chemical or nuclear process 

 in which some of the products of the process or 

 energy released by the process are instrumental 

 in the continuation or magnification of the proc- 

 ess. (70) 



chalk — A very soft white to light gray limestone 

 composed of the tests of floating microorga- 

 nisms and some shells of bottom dwelling ani- 

 mals in a matrix of finely crystalline calcite. 

 Chalk is classed as rock on bottom sediment 

 charts. (2) 



Challenger Expedition — The expedition 

 mounted by the British in H.M.S. Challenger, 

 1873-1876, wliich made the first extensive 

 oceanographic research cruise. 



change of tide — (or turn of the tide). A re- 

 versal of the direction of motion (rising or fall- 

 ing) of a tide. Sometimes applied to a reversal 

 in the set of a tidal current. 



channel — 1. A natural or artificial waterway 

 which either periodically or continuously con- 

 tains moving water, or which forms a connect- 

 ing link between two bodies of water. (61) 



2. The part, of a body of water deep enough 

 to be used for navigation through an area other- 

 wise too shallow for navigation. (61) 



3. A large strait, as the English Channel. 

 (61) 



4. The deepest portion of a stream, bay, or 

 strait through which the main volume or current 

 of water flows. (61) 



6. A lead in pack ice. (59) 



6. An energy band of predetermined size used 

 in the discrimination and storage of electronic 

 pulses like those from a gamma ray spectrom- 

 eter probe. See pulse height analyzer. 



channel wave — Any elastic wave propagated in a 

 sound cliannel because of a low velocity layer in 

 the solid earth, the ocean, or the atmosphere. 

 (35) 



chapeirao — A Brazilian term for isolated coral 

 structures, which often rise to a height of 40 to 

 50 feet like towers, sometimes spreading out in 

 a mushroomlike top. (2) 



characteristic wave height — See significant 

 wave height. 



character of the bottom — (also called nature of 

 the bottom) . The type of material of which the 

 bottom is composed and its physical character- 

 istics such as hard, sticky, and rough. 



chart — A special-purpose map generally designed 

 for purposes of navigation. The term is some- 

 times used to describe other special-purpose 

 maps. (37) 



chart datum — (or datum, datum plane, hydro- 

 graphic datum plane of reference, reference 

 pltine, tidal daimn). The permanently estab- 

 lished surface from which soundings or tide 

 heights are referenced (usually low water). 

 The surface is called a tidal datum when re- 

 ferred to a certain phase of the tide. In order 

 to provide a factor of safety, some level lower 

 than mean sea level is generally selected, such 

 as mean low water or mean lower low water. 

 {See figure for tide range.) 



charted depth — The vertical distance from the 

 tidal datum to the bottom. (68) 



Charybdis — See Galofaro. 



chemical oceanography — The study of the chem- 

 ical composition of the dissolved solids and 

 gases, material in suspension, and acidity of 

 ocean waters and their variability both geo- 

 graphically and temporally in relationship to 

 the adjoining domains, namely, the atmosphere 

 and the ocean bottom. 



chemiluminescence — The production of light 

 during a chemical reaction at low temperatures. 

 Bioluminescence is a chemiluminescent reac- 

 tion. 



chemistry of sea water — See constituents of 

 sea water. 



chemoautotrophic nutrition — See chemotrophic 

 nutrition. 



chemotrophic nutrition — (or chemoautotrophic 

 nutrition). That process by which an orga- 

 nism manufactures its food by using the energy 

 derived from oxidizing organic matter. See 

 autotrophic nutrition. 



Chile Current — See Peru Current. 



chip log — A line marked at intervals (commonly 

 50 feet) , and payed out over the stern of a mov- 

 ing ship. By timing the intervals at which the 

 markers appear as the line is pulled out by a 

 drag (the "chip"), the ship's speed can be de- 

 termined. The wavelength of ocean waves can 

 be estimated by noting the position of wave 

 crests relative to the markers. (5) 



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