deep oceans. At a depth greater than 200 fathoms, 

 the temperature everywhere Is below 60 degrees F, 

 and in the deeper layers, fed by cooled waters 

 that have sunk from the surface in the arctic ana 

 antarctic, temperatures as low as 33 degrees F 

 exist. 



It is only in the deepest ocean basins, at 

 depths greater than 2,000 fathoms, that the heat 

 of the earth's crust influences the water tempera- 

 ture. In such basins the temperature shows a 

 slight increase with depth, seldom amounting to 

 more than 1 degree F. (12) 



TEMPERATURE PROFILE RECORDER (TFR) . The Tempera- 

 ture Profile Recorder is a portable unit consist- 

 ing of a thermistor sensing element, 6-volt power 

 supply, amplifier, and a recorder. The recorder 

 is geared to a drum containing an electrical cable 

 to which the bead is fastened. When the bead is 

 lowered into the water, the paper on the recorder 

 is moved accordingly. Depth is measured by the 

 amount of wire paid out. This device is used in 

 shallow water, particularly in lakes. (35) 



TEMPERATURE-SALINITY DIAGRAM . (Abbreviated T-S 

 diagram.) A graph with temperature as ordinate 

 and salinity as abscissa, on which the points ob- 

 served at a single oceanographic serial station 

 are Joined by a curve (the T-S curve) . (24) 



TEMPORARY PLANKTON . See MARINE LIFE. 



TENOC. Ten-year oceanographic program (Navy) . 



TENSILE MODULUS OF ELASTICITY . Also called Modulus 

 of Elasticity in Tension and often merely Modulus 

 of Elasticity. The tangent or secant Modulus of 

 Elasticity of a material in the Tension Test. The 

 relationship between Tensile Stress and Tensile 

 Strain. 



TENSILE STRENGTH . The Ultimate Strength of a 

 material subjected to tensile loading. The maxi- 

 mum Tensile Stress developed by a material in the 

 Tension Test. It is calculated by determining the 

 Tensile Stress corresponding to the maximum load 

 observed in the Tension Test. For ductile metals 

 Tensile Strength of a material is usually greater 

 than its Breaking Strength, but is well below the 

 maximum true stress developed by the material. 

 Tensile Strength is a common index for strength 

 comparison of materials. It may be directly use- 

 ful in design where some plastic deformation is 

 permitted, but Yield Strength is the common basis 

 for elastic design. Tensile Strength may also be 

 some indication of allowable severity of hot and 

 cold working processes. 



TENSILE STRESS . Sometimes called Modulus. The 

 nominal stress developed by a material subjected 

 to a specified stretching load, as in the Tension 

 Test. Above the Elastic Limit, nominal Tensile 

 Stress is considerably lower than the true stress 

 because it does not reflect the decrease in cross- 

 section area accompanying continued deformation. 



TENTED ICE . A type of pressure ice created when 

 ice is displaced vertically upward, forming a flat- 

 sided arch with a cavity between the raised ice 

 and the water underneath. (17) 



TENTING . The vertical displacement upward of ice 

 under pressure to form a flat-sided arch with a 

 cavity beneath. (17) 



TERDIURNAL . Having three periods in a constituent 

 day. The symbol of a terdiurnal constituent is 

 usually distinguished by the subscript 3. (14) 



TERRACE . A bench- like feature bordering an eleva- 

 tion of the sea floor. A terrace does not include 

 the CONTINENTAL SHELF or ISL-MTO SHELF, but may in- 

 clude bench-like features on the shelf. (26) 



TERRIGENOUS . Of the land. When applied to ocean 

 bottom deposits, it denotes those that are composed 

 predominently of material brought from the land. 

 The continental shelves are covered almost entirely 

 by terrigenous deposits. (27) 



TETRASPORE . One of the haploid asexual spores in 

 the red algae developed meiotically and commonly in 

 groups of four from the diploid tetrasporangia and 

 germinating to produce the haploid gametophytic 

 plants. (20) 



TETRAXON . See SPICULE. 



THALLUS . A type of plant body which is undifferen- 

 tiated into root, stem, or leaf. (18) 



THALWEG . 1. The line joining the lowest points 

 of a valley or a submarine valley. 



2. The center line of the principal 

 navigational channel of a waterway constituting a 

 boundary between political subdivisions. (17) 



THEODOLITE . An optical micrometer-reading instru- 

 ment in which two diametrically opposed axes are 

 brought to coincidence and read through a micro- 

 scopic eyepiece. This angle and distance measur- 

 ing instrument is used, for example, in certain 

 types of geodetic field survey work. (29) 



THERMAL EXHAUSTION . The underwater swimmer is ex- 

 tremely sensitive to moderate changes in water tem- 

 perature in both directions because water is a 

 much better heat conductor than air. At present 

 there is no equipment to protect a man against 

 moderately warm water. Heat prostration may occur 

 during exercise in water around 86°F. and at rest 

 in water around 96°F. 



A much commoner stress is water colder than 

 65° to 72°F. Many types of clothing have been de- 

 vised to protect against cold water. Unfortunately 

 most have obvious handicaps such as loss of protec- 

 tion when wet inside, limitation of motion, SQUEEZE 

 and chafing at depths, marked buoyancy changes at 

 depth and lack of a mechanism to rid oneself of 

 sweat and excreta. (37) 



THERMAL NOISE . Even if it were possible to isolate 

 a sample of water completely from all external in- 

 fluences there would still be minute movements of 

 the molecules, due to thermal agitation, accom- 

 panied by the release of acoustic energy. This 

 molecular agitation, which is proportional to the 

 absolute temperature of the water, is spoken of as 

 thermal noise. (4) 



THERMAL PROBE . A device used for measuring the 

 heat flow out of ocean bottom SEDIMENT. 



THERMISTOR . An electrical resistor made of a 

 material whose resistance varies sharply in a known 

 manner with the temperature. 



Thermistors are commonly used for shipboard 

 oceanographic temperature measurements because of 

 their percentage response to unit temperature 

 change and their great sensitivity. 



THERMOCLINE . A vertical temperature gradient in 

 some layer of a body of water, which is appreciably 

 greater than the gradients above and below it; also 

 a layer in which such a gradient occurs. The prin- 

 cipal thermoclines in the ocean are either seasonal, 

 due to heating of the surface water in summer, or 

 permanent. (24) 



THERMOMETER FLOAT . This instrument: is used for 

 studying the temperature structure in the upper 10 

 meters of water. The instrument is in two sections; 

 a float which contains a spooling winch from which 

 the sensing unit is lowered, and an indicator case 

 which contains the remote indicating equipment and 

 remote control system. The two sections are con- 

 nected by an electric cable and flexible shaft. 



119 



