PILOT CHART 



field produces corresponding changes in dimen- 

 sions. 



Pilot Chart — A chart of a major ocean area pub- 

 lished, for the benefit of mariners, by the U.S. 

 Naval Oceanographic Office in cooperation with 

 the U.S. Weather Bureau. These charts con- 

 tain information required for safe navigation, 

 including ocean currents, ice at sea, wind roses, 

 storm tracks, isotherms, magnetic variation, 

 great circle routes, limits of trade winds, etc. 

 See sailing directions. 



pilot whale — (or ilacJcfish) . Any of several spe- 

 cies of a genus {GlobiceplialcL) of large dolphins, 

 having worldwide distribution. These animals 

 commonly travel in schools, and many strand- 

 ings of them have been reported. 



pinching — See nipping. 



ping — An acoustic pulse signal projected by an 

 underwater transducer. 



pinger — A battery powered acoustic device 

 equipped with a transducer that transmits 

 sound waves. When the pinger is attached to a 

 wire and lowered into the water, the direct and 

 bottom reflected sound can be monitored with 

 a listening device. The difference between the 

 arrival time of the direct and reflected waves 

 is used to compute the distance of the pinger 

 from the ocean bottom. 



pingo — A hill or mountain completely covered by 

 an ice sheet, but revealing its presence by sur- 

 face indications. (2) 



pinnacle — A sharp pyramidal or cone-shaped rock 

 partly or completely covered by water. Also a 

 small coral spire which lies near the water sur- 

 face in a lagoon. 



pinnacled iceberg — An iceberg formed and 

 weathered in such manner as to produce spires 

 or pinnacles. (68) 



pinniped — A marine mammal of the order Pimii- 

 pedia, whicli comprises the seals, sea lions, and 

 walruses. 



pinpoint — See fix. 



pip — An echo trace on an electronic indicator 

 screen. 



pisolites — Rounded granule-sized concretions 

 larger than oolites, found in land and marine 

 deposits. They form pisolitic limestone when 

 cemented togef;her. 



pistol shrimp — See snapping shrimp. 



piston-type corer — A corer equipped with a pis- 

 ton inside the core tube that is connected to the 

 lowering cable. When the corer penetrates the 

 ocean bottom, the piston, in effect, provides a 

 suction which overcomes the frictional forces 

 acting between the sediment sample and the in- 

 side wall of the coring tube. See Kullenberg, 

 Ewing, and Hydroplastic corers. 



pitch — See ship motion. 



Pit log — Short form for Pitometer long. 



Pitometer log — A log consisting essentially of a 

 Pitot tube projecting into the water, and suit- 

 able registering devices. (68) 



plain — A flat, gently sloping or nearly level 



region of the sea floor. (62) 

 Planck's constant — A natural constant of propor- 

 tionality (A) relating the frequency (v) of a 

 quantum of energy to the total energy {E) of 

 the quantum : 

 W 

 \\= — =6.624 X 10-=' erg-sec. 



(70) 

 plane of reference — See chart datum, 

 planform — The outline or shape of a body of 



water as determined by the still water level. 



(61) 



plankter — A single organism in the plankton. 



plankton — The passively drifting or weakly swim- 

 ming organisms in marine and fresh waters. 

 Members of this group range in size from micro- 

 scopic plants to jellyfishes measuring up to 6 

 feet across the bell, and included the eggs and 

 larval stages of tlie nekton and benthos. Se& 

 phytoplankton, zooplankton. 



plankton bloom — (or sea Moom). An enormous 

 concentration of plankton (usually phyto- 

 plankton) in an area, caused either by an ex- 

 plosive or a gradual multiplication of organisms 

 (sometimes of a single species) and usually pro- 

 ducing an obvious change in the physical appear- 

 ance of the sea surface, such as discoloration. 

 Blooms consisting of millions of cells per liter 

 often have been reported. See red tide. 



plankton centrifuge — A device for separating 

 plankton from water samples by centrifugal 

 force. 



plankton equivalent — A relationship between 

 various chemical constituents or cliaracteristics 

 of plankton whereby the measurement of one 

 characteristic can be used to derive the quantity 

 of other characteristics. In phytoplankton 

 studies, 1.0 milligram (mg) of carbon is equiva- 

 lent to 2.3 milligrams of dry organic matter, 

 42.0 milligrams of biomass, and 3.3 milligrams 

 of dry plankton. In zooplankton studies, 1.000 

 milligram of carbon is equivalent to 0.170 milli- 

 gram of nitrogen, 0.013 milligram of phos- 

 pliorus, 8.300 milligrams of plankton biomass, 

 and 1.700 milligrams of dry plankton. 



plankton haul — (or plankton tou\ haul, toiv). A 

 single tow of a plankton net. 



plankton indicator — See plankton sampler. 



plankton net — A net for collecting plankton. A 

 great variety of plankton nets have been con- 

 structed in attempts to fulfill specific require- 

 ments. Typically, the nets are cone shaped, but 

 several modifications of this shape as well as 

 completely different shapes exist. Variations in 

 design involve: mouth diameter, net length, 

 mesh aperture size, material, type of collecting 

 bucket, and opening or closing capability. Many 

 nets are used without any attachment (except 

 the necessary collecting bucket and mouth ring) . 

 Others are attached to hollow cylinders bearing 



124 



