CHAPTER A 



INTRODUCTION 



A-1 Oceanography, a Definition. — Oceanog- 

 raphy is the study of the sea, embracing and 

 integrating all knowledge pertaining to the 

 sea's physical boundaries, the chemistry and 

 physics of sea water, and marine biology. 



A-2 The Types of Information Sought. — In 



the sense that oceanography encompasses por- 

 tions of all the physical sciences, types of in- 

 formation sought on oceanographic surveys and 

 expeditions include data from these fields. 



Because of the high costs of maintaining a lab- 

 oratory, such as a ship needed to obtain oceano- 

 graphic information, the most profitable use 

 must be made of its time at sea. Although a 

 particular project may concern itself primarily 

 with a certain oceanographic feature, other sup- 

 porting data fi'om any other variables usually 

 are requii'ed. For example, investigations of the 

 growth of plankton become inunediately in- 

 vohed with water temperatures and salinities, 

 nutrient concentrations, transparencies, and 

 mass transport of water. Information pertain- 

 ing to these variables requires, in turn, related 

 obsen^ations of air temperatures and other 

 meteorological data. 



Inasmuch as characteristics of the sea may 

 change with respect to both space and time, the 

 periodicity and extent of these changes must be 

 investigated. Conditions that vary with time 

 may need to be observed during repeated sur- 

 veys of the same area, whereas conditions that 

 change from place to place should be measured 

 by simultaneous observations taken throughout 

 an area from two or more ships or recording 

 units. 



Oceanography may be divided into five basic 

 sciences: Physics, chemistry, meteorology, biol- 

 ogy, and geology. A few comments concern- 

 ing the general types of information sought in 

 eacli of the fields are given below. 



A-3 Physical Oceanography. — Physical 

 oceanography is probably the largest and most 

 diversified of tlie five basic divisions. Its study- 

 involves all the other fields, especially chemical 

 oceanography. It includes tides, currents, sea 

 and swell, temperatures, densities, origin and 

 circulation of water masses, sound propagation, 

 t ranspai'ency, sea ice, and other physical proper- 

 ties of sea water. 



Of major importance is knowledge concern- 

 ing surface and subsurface currents — whence 

 they originate, their speed and direction, and 

 their influence on other oceanic factors. Deter- 

 minations of subsurface currents may be made 

 by direct measurements with current meters, 

 or by mathematical computations utilizing the 

 densities of the masses in question. 



Density is a function of the temperature and 

 salinity of the water under a given pressure. 

 It is desirable, therefore, to gain knowledge of 

 the vertical distribution of temperatures and 

 salinities at accurately determined depths. These 

 variables also provide basic information re- 

 quired to determme sound propagation patterns, 

 both vertically and horizontally, in sea water. 



Internal waves have concerned investigators 

 in the field of underwater sound transmission. 

 These waves are similar to the commonly ob- 

 served surface waves but occur at the interface 

 of layers of water of different densities rather 

 than at the sea-air boundary. The study of wind 

 waves (sea) and swells, until a few years ago, 

 has been limited mainly to observations of deep- 

 water waves by visual means. Recent develop- 

 ments of pressure-operated wave indicators, 

 however, provide new types of recorded data for 

 analyses. The success of research into long- and 

 short-range wave forecasting from meteorologi- 

 cal data is dependent upon the number of ob- 

 servers reporting and the accuracy of the ob- 

 servations. Such forecasts are of utmost value 

 for many marine operations, including military, 

 commercial, and scientific. 



Observations of water transparency, light 

 penetration, light scattering, and water color 

 are aided by the use of photoelectric cells which 

 are lowered to various depths. Such studies as- 

 sist in the determination of currents and pro- 

 vide clues to biological influences. 



A-4 Chemical Oceanography. — The field of 

 chemical oceanography is concerned with the 

 determination of the various constituents of sea 

 water and their distribution. The salinity of 

 sea water is required in computing densities 

 and dynamic currents as well as sound veloci- 

 ties. Analyses to determine nutrient concentra- 

 tion (phosphate, nitrate, silicate, etc.), pH 

 (acidity), and concentration of dissolved gases 

 (oxygen and carbon dioxide) provide informa- 



A-1 



