Oceanography, the geography of the ocean, is of peculiar interest to the Navy, for it was our own Matthew Fontaine Maury who gave that branch of science its greatest impetus, during the middle of the last century. His fame is just as great abroad, for his contributions to the knowledge of ocean depths and circulation and of oceanic meteorology are remembered gratefully by the scientific world. The present-day pilot chart of the Hydrographic Office, so useful to the mariner, is a monument to his genius and industry.
The story of the expeditions contributing to the science of oceanography is of absorbing interest. Among these expeditions may be mentioned the United States Exploring Expedition of 1838-42, headed by Lieutenant Charles Wilkes, U.S. Navy, the British Challenger cruise around the world, 1872-76, the Norwegian-British expedition on the Michael Sars in 1910, and the German Meteor cruise of still later Years. Our own ill-fated Carnegie, while primarily engaged in magnetic work, gathered a vast amount of oceanographic and meteorological data, and established many of the factors for the correction of echo soundings for variations in the underwater velocity of sound.
The Navy's contribution to the science of oceanography in the nineteenth century was very great. In more recent years the Navy has lagged behind, just when newer methods and more accurate instruments have begun to open fields of vast possibilities. Among the new or improved devices which have come into use are echo sounding equipment, more accurate thermometers for obtaining surface and subsurface temperatures, and more reliable reversing bottles for carrying thermometers to the depths and for impounding water samples for analysis. Of even greater importance from the mariner’s point of view are new discoveries and studies in the field of hydrodynamics which have provided methods by which currents are calculated from densities of sea water at various levels and at suitably chosen stations. The field is now open to scientific dynamic surveys of the seas for current determination by methods which promise to cover areas in weeks that would take years by the old methods of compiling, evaluating and analyzing data furnished by observers.
These methods require vessels properly equipped for the purpose, and men are needed to work the ships. In contrast to most branches of geophysics, individuals or small groups and modest purses have- seldom been able to make important advances in oceanography. The Navy has both ships and men which might from time to time be made available without detriment to other activities, at slightly greater cost than maintenance.
It can easily be shown that the Navy can be of great use to the science of oceanography. But of what value is oceanography to the Navy? In these days of rigid economy in governmental expense the Navy cannot justify its efforts for the advancement of science unless it can be shown that the Navy is benefited directly or indirectly by such work, for eventual economy, for military objectives, or for increased safety of the fleet. It is the purpose of this paper to show that such benefits can be expected.
In an earlier paragraph oceanography was defined as the geography of the ocean. Oceanography impinges upon many other branches of geophysics and, although a physical science, it has phases in common with biology, zoology, and botany. Oceanography deals primarily with the physical and chemical properties of the waters of the oceans and the movements of these waters, the contours and character of the bottom, and to a lesser degree with the littoral of the coasts bounding the seas and the meteorology of the atmosphere directly over them.
In recent notable meetings of scientists visitors have been impressed by the interest of geophysicists in the developments of oceanography and by the very close relationship that science bears to other branches of geophysics, such as seismology, volcanology, meteorology, hydrology, and geology. These and others look to oceanography to supply the answers to some of their own unsolved riddles. They want more accurate delineation of the contours of the ocean bottom, and more information as to currents, weather, water temperatures, chemical constituents, and the flora and fauna of the seas.
Seismologists desire a better and more accurate bathymetric picturization of the ocean bottom, from this to discover more of the whys and wherefores of earthquakes. Meteorologists, noting a similarity between the circulation of the oceans and that of the atmosphere, seek to find a definite relationship. People interested in fisheries are looking to oceanography to point the way to new fishing grounds or to explain why the fish move from old to new grounds. Even the anthropologists hope that oceanography may throw light on the migration of the human species, especially the Polynesians, on the assumption that ocean currents must have had some influence on the remarkable spread of these peoples in the Pacific. It is believed that a study of these currents may conceivably show whence they came, and how and where they went. And by similar study the botanist may obtain information of the movements of the current carried seeds, such as coconuts.
The Navy’s interest in oceanography.—The Navy in its hydrographic surveying projects and in its work of collecting information on currents for the compilation of the pilot charts is contributing directly to oceanographic lore, and the value of such work is too obvious to require any elaboration, affecting as it does the safety of the mariner, and therefore the safety of the fleet. Such knowledge makes not only for the safety of the ships and men against the dangers of the sea, but may enable our leaders to take advantage of currents and weather in order to gain a tactical or strategical advantage over an enemy.
Now that ships generally are being equipped with echo sounding devices, and are attaining a high degree of accuracy in their operation, there is an increasing demand for some kind of bathymetric chart a chart which shows accurate contour lines of the ocean bottom. Many navigators are convinced that the problem of navigating their ships with safety and economy, especially in thick weather, will be much easier when more reliable and more detailed soundings are entered on charts. In the North Atlantic soundings are numerous, but in the North Pacific there are many blank spaces—unsounded areas—and in the South Pacific there are only a few scattered lines of soundings. The Navy has always considered itself justified in its efforts to take soundings and to reduce the unsounded areas as much as possible, and it is reasonably certain that we shall continue in the forefront of this work.
A difficulty in the use of echo soundings arises from the difference in the velocity of sound in water of varying densities. This introduces an error in the sounding which may or may not be serious according to the existing conditions or requirements. For navigating by soundings, it would certainly appear necessary to correct the echo soundings. Fortunately for the determination of correction factors density distribution is such that comparatively large areas are of an approximately uniform density. The correction factors are obtained by temperature and salinity observations in vertical sections at various stations.
Our knowledge of currents, from the time Maury first published the results of his researches, has been derived almost entirely from the collection of current data from observers, who calculate ocean currents from the difference between the dead reckoning run for a given period of time and the actual run as determined by fixes. Concededly there is likely to be considerable error in any individual report, and therefore such a method might be considered unscientific. But a multiplicity of observations tends to correct individual errors, so that current set and drift deduced from a great mass of data can be relied upon. In spite of the labor of collecting, sorting, and analyzing such data, it appears to be the best method for the determination of currents in areas where there are well-traveled routes, where there will certainly be enough observations to be sure of the results of the work. But in areas where there are no regular trade routes, data are lacking because the information and reports received are insufficient for current determination. In these areas, which perhaps may be of the utmost strategic importance, the only hope for accurate information lies in the new dynamic surveying methods, and the Navy cannot look to other agencies for this information.
Meteorological data and surface temperature data used in connection with current charts have seldom been considered the factors of great strategical importance that they really are. We are discovering many things contrary to old opinion, such as that fog does occur in tropical sea areas and that there exist cold and warm currents in many places almost side by side, even near the equator. A commander in chief knowing that certain currents were sending warm water to a certain locality, and that winds the next day would carry moisture-laden air from that point toward and over a cold current, would realize the probability of fog or thick weather, and act accordingly. The Navy cannot afford to neglect such sources of information, if advantage is to be taken of every possible circumstance.
Oceanographic equipment.—No attempt will be made to discuss any equipment not required for the kind of work in which the Navy’s interest may be centered. For this we need little more than an echo sounding device, and a means for entrapping water samples at various depths for salinity determination, and for taking the temperatures at those depths. The last-named functions are taken care of by metal water bottles carrying a special type of thermometer, spaced as desired along the sounding cable. These bottles are ingeniously designed to capture a generous sample of sea water at the specified depth, and also to effect the reversal of the thermometers they carry—this reversal being the means by which the record of the temperature may be brought to the surface. A small projectile-like weight is used to slide down the cable and actuate the mechanism, a process that is carried through to the last bottle.
Deep-sea thermometers have several points of difference from the ordinary thermometer, but the chief feature is a gooseneck or constricted area in the capillary tube above the mercury reservoir. Reversal of the thermometer results in a break at the constricted part of the tube. The length of that part of the column formerly above the break (but now below it) read on its scale gives the temperature of the place of reversal, subject to the application of a small correction due to the temperature of the air at the time of reading. This temperature is found by a comparison with the auxiliary thermometer attached. (See Fig. 2, in which A is the main thermometer, B the auxiliary, C the constricted part of the tube, and D a mercury bath around reservoir.)
Two types of reversing thermometers must be employed. One thermometer, protected from pressure by a strong glass tube surrounding it, is used for the actual determination of the temperature; the other, open to the sea pressure, is for an entirely different purpose. This unprotected thermometer gives a fictitious reading higher than that of the protected thermometer; the difference, being proportional to the pressure, provides an accurate method of checking the depth.
Dynamic current determination.—The terms "dynamic soundings" and "dynamic oceanographic survey" are used to designate investigations of oceanic circulation by consideration of the specific gravity from observations of temperatures and salinities in vertical sections. The specific gravity of sea water (commonly called density) is dependent upon the amount of solids contained in the water but must be referred to a standard temperature. For dynamic investigations, a specific gravity of 1.02537 is expressed for convenience and brevity as 25.37.
Computations may be made from the temperature and salinity data gathered at various depths at a given station to obtain a measure of pressure which may be expressed as a height in dynamic meters above an isobaric plane. By occupying a number of stations suitably chosen, lines of equal dynamic height (depth) called isobaths may be drawn, which will give patterns similar to the well-known isobars of weather maps. Figures 3 and 4 are examples of current maps, showing systems of lows and highs. The mean surface of the water in the highs is actually higher than that in the lows, as it is water of less specific gravity, and a flow of current will result from a high to a low. Owing to the rotation of the earth and other causes, there will be a deflection of about 90 degrees, and as a result counter-clockwise currents will be set up around centers of low dynamic heights, approximately parallel to the isobaths, and clockwise currents around the high centers.
Actual computation of the current can be made only of the component perpendicular to the line joining two stations, but by the proper choice of stations a rather thorough study of conditions can be made. A difference of one centimeter per mile in the dynamic level will produce a current of about 1.3 knots. Lines of stations are generally chosen at right angles to the estimated set of the current, but if circumstances permit, a network of stations is to be preferred. Both of these may be seen in Fig. 1, showing stations occupied by the U.S.S. Hannibal during the survey season of 1932-33.
For the study of current circulation only, deep soundings are not necessary, for below a certain depth the water will [be found to be of uniform density. Fairly accurate results have been obtained by soundings of 750 meters, using 6 or 7 bottles. This was the first procedure followed by the U.S. Coast Guard in their investigations of ice drift in connection with the International Ice Patrol, but later a depth of 1,000-1,200 meters was favored as giving more accurate results. For extreme accuracy in deep water it is probable that soundings should be made to 3,000 meters, and of course there are good reasons for making soundings to the bottom in a systematic deep-water survey. In deeper water some 18 samples and temperature ratings will be required, and it is usually convenient to make two casts, using about half the total number each time.
It is of great importance to determine accurately the depth of each bottle of the series. If the cable tended vertically or at a constant angle, the true depths could easily be found by consideration of meter wheel readings and the measured wire angle. Unfortunately such a condition is the exception; as a rule the wire is likely to form a decided curve, so it becomes necessary to use the unprotected thermometer referred to in the previous section. As many of these as may be required are used, each in addition to a protected thermometer in the carrier of a water bottle. The difference of readings provides a means for calculating the depth at the points selected, and intermediate depths are determined by proportion to the spacing. It is considered good practice to have such a pair in the bottom bottle, and in every alternate bottle.
The ship is hove to and the depth is ascertained as accurately as possible by echo sounding, and an estimate made of the probable wire angle and therefore of the length of cable required for the sounding. A tentative layout of the bottle spacing is put on the record sheet, later changing it to conform to the actual wire angle. Bottles are made ready, fitted with thermometers, and sent overside, careful records being made of thermometer numbers, meter-wheel readings, and all pertinent data. The series of bottles having been lowered away and sufficient time having elapsed to ensure correct thermometer readings, the first messenger weight is put on the cable and allowed to slide down to begin the series of operations of closing water bottles and reversing the thermometers. This may take 20 minutes. The wire is then hove in, removing bottles, drawing off water samples, and reading thermometers. The whole operation may take from 20 minutes to 3 hours depending on the depth.
Salinity determination may be made on the ship or water samples may be placed in properly sealed containers and later examined at the laboratory. The determination of the salinity is generally made by the titration of the chlorides against a sample of "standard" sea water. This method is similar to the Navy's process of determining the salinity of boiler water, using nitrate of silver with potassium chromate as an indicator, but is carried out more accurately—to the nearest 0.01 part in a thousand. The titration method is made possible because the salts of sea water are of such uniform composition that the chlorine in all cases bears a constant ratio to the total salinity. An average figure for salinity is 35. This means that 1 kilogram of that water contains 35 grams of halogen (salt content), i.e., 35 parts per thousand.
Summary of oceanographical investigations.—Those activities which can be considered of direct interest to the service appear to be:
- Hydrographic surveying in areas where the Navy or American shipping or commercial interests need such services.
- Determination of figures for the reduction of echo soundings.
- Accurate and complete soundings of all the oceans.
- Investigation of oceanic circulation, both by collection and analysis of observers' reports and by making dynamic surveys, as this directly affects navigation, ice drift, climates, fisheries, etc.
- Accumulation of data concerning surface temperatures, including the study of the relationship of these temperatures to meteorological conditions.
Other aspects of oceanography, while not clearly of direct benefit to the Navy, are nevertheless of great scientific value and have greatly aided the advancement of civilization. Much oceanographical work has been accomplished incidental to researches primarily for biological information, and for the expansion of knowledge of the distribution, reproduction, habits, and abundance of marine animals and plants. Studies of gravity, of terrestrial magnetism, of the great submarine deeps and ridges, of submarine sediments for their geological bearings and as possible future sources of oil, of the radio activity of the bottom, and of the formation, dimensions, and speed of ocean waves are some of the other investigations claiming the interest of scientists.
Recent work of the Navy.—In the Navy’s studies of oceanic circulation, the assistance of volunteer observers on merchant vessels has been, and continues to be, of prime importance. The work of correlating the data by the Hydrographic Office is a work of magnitude and must necessarily progress slowly. As before stated, the Hydrographic Office will be able to depict with confidence the currents of all the oceans where vessels regularly ply their trade, but in many vast areas there are not enough data to be able to do much more than make assumptions. It is in such areas that dynamic sounding methods appear to offer promise of a more complete knowledge of oceanic circulation.
During the past year considerable progress was made by vessels attached to regular hydrographic surveying expeditions in dynamic soundings, as opportunity offered during the progress of their assigned work. The U.S.S. Hannibal occupied a total of 144 stations. Of these 7 were in the Atlantic and Caribbean, 85 in a network covering the Gulf of Panama, and 52 in the littoral waters of Panama and Costa Rica, extending about 200 miles from Cape Mala. (See Fig. 1.) The U.S.S. Gannet occupied 42 stations in the Aleutian Islands, making temperature observations and obtaining 455 water samples.
Other work of value has been the series of soundings made by various ships using echo sounding devices. Many of these have been in areas where comparatively few data have existed, or where the new information served admirably to complement information at hand. The U.S.S. Ramapo made some 25 crossing of the Pacific by different routes, making soundings about every 5 miles. The publication of these soundings from time to time has aroused lively interest among scientists, and has enhanced the prestige of the Navy. These soundings for the most part are uncorrected for velocity of sound, and the corrections are not yet available for all parts of the world, but eventually will be obtained by dynamic soundings. For the Ramapo’s soundings a velocity of 4,800 feet per second is used.
Figure 5 depicts a phase of the Navy’s work which in the strictest sense would not ordinarily be classed as oceanographic work, but is included as a typical example of a certain type of activity not familiar to everyone. Reports of the grounding of several vessels on Mucaras Reef in the Bahama Channel led to the assignment of the Nokomis to make an investigation, with the consent of the British government. The expansion of the triangulation from main triangulation stations of the Navy’s Cuban survey is shown. The results of this survey place the reef 1 mile farther south and three quarters of a mile farther west than previously charted.
U. S. organizations active in oceanography.—The Hydrographic Offices and private institutions of many nations have been active in recent years, and information is constantly being accumulated- Many of the foreign navies have vessels specially fitted for oceanographic work- Because of the vastness of the field to be covered, oceanographers are endeavoring to map out a comprehensive plan for the future, in which they tentatively assign certain work and areas to various public and private organizations. They hope and expect that the U. S. Navy will do its part.
In the United States several government agencies are engaged in oceanographical work. The Coast Guard, in its cooperative work in connection with the International Ice Service, makes systematic dynamic oceanographic surveys in northern latitudes and near the Grand Banks, and has achieved considerable success in the prediction of ice drift. The 125-foot patrol boat General Greene is specially fitted for oceanographic work and is able to make determinations and construct current maps in the field. The Bureau of Fisheries does considerable work, some of it in conjunction with expeditions of other institutions, attacking the problem chiefly as it relates to the great fisheries industry.
Three private oceanographical institutions are active in dynamic oceanography. These are the Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, the Scripps Institute of Oceanography, La Jolla, California, and the Department of Oceanography of the University of Washington, Seattle, Washington. The Carnegie Institute, Washington, D. C., continues to be interested in oceanography, although the loss of the Carnegie by fire has necessarily curtailed that phase of its work.
In its work the Navy has found all of these institutions most helpful and willing to co-operate, and very pleasant relations with all of them are maintained.
Conclusion.—That the Navy will continue to play a part in the extension of oceanographic knowledge cannot bedoubted; just how great a part lies in the future, and is dependent upon budgetary limitations and questions of policy. There is nothing startling or radical in the suggestion that the Navy should actively engage in the extension of oceanographical knowledge. On the contrary it is a matter of policy, which goes back to the “Schofield Board” of 1929, approved in that year by the Secretary of the Navy.
The Secretary of the Navy appointed Rear Admiral Frank H. Schofield, U.S. Navy, Captain C. S. Kempff, U.S Navy, and Captain C. S. Freeman, U.S. Navy, members of a board on oceanography to study the problem with a view to determining (1) how the Navy could best assist in the accumulation of additional oceanographic information, and (2) what class of information was best adapted for the Navy’s attention at that time.
Part of the board’s report is quoted:
It appears from a consideration of the information before the board that there are two general classes of oceanographic work which the Navy might undertake.
Class 1 includes all those investigations of the sea that require the services of a vessel devoted exclusively to such work. These investigations include a detailed examination of specific localities as to animal life, currents, temperatures, salinity of water at varying depths, temperatures of water at varying depths, character of the bottom contours, of abnormal formation of the bottom, and allied subjects.
Class 2 includes those investigations of the sea that may be undertaken by vessels on their regular voyages, provided they are fitted out and instructed in the use of standardized instruments for determining depths, for the taking of temperature observations of the air and the surface of the water, and for obtaining salinity samples of surface water.
As to class 1, while it is believed exceedingly desirable from the standpoint of general oceanographic knowledge to fit out and employ a vessel of the Navy on this class of work, the board, having in view the budgetary limitations of the Navy and the non-availability of personnel, does not recommend that this class of investigation be undertaken at this time. Should future conditions be more favorable to the undertaking, the board strongly recommends in the interest of general science and in the specific development of oceanographic information that such work be undertaken by a vessel of the Navy specially fitted for the enterprise.
As to class 2 operations, the board, after careful consideration of the subject, finds that it would be desirable and practicable for the Navy to undertake this class of work as incidental to its normal operations. There are now very large areas of the sea over which no surveys have been made to develop the contours of the ocean bottom. . . .
The board made a careful study of unsurveyed parts of the oceans, particularly as to depths, temperatures and currents, and made recommendations that a world chart showing unsurveyed areas of the oceans be issued to the service; that instructions be issued to naval vessels to take soundings in unsurveyed areas when their operations permitted; and that the Navy Department designate particular lines of soundings for vessels making passages at sea. Referring to these particular recommendations the board said:
The preceding recommendations are based upon the idea of a systematized and co-ordinated effort in developing contours of the ocean bottom.
The spirit and letter of these are being carried out, and considerable information of great value has been accumulated. Other recommendations do not bear directly upon the problem immediately under discussion, except perhaps the recommendation that suitably equipped vessels operating in the vicinity of the ocean deeps be directed as circumstances permit to make surveys according to a standardized plan to be prepared. The last paragraph of the report is quoted:
In conclusion the board stresses its opinion that it is highly desirable for the Navy to undertake the class of work above indicated. While the direct and immediate contributions to oceanographic knowledge may not appear to be of great practical use, the board is convinced that the possibilities involved in the accumulation of the data outlined may result in valuable conclusions permitting weather, current, and other predictions of sufficient importance fully to justify the effort.
The Navy is endeavoring to carry out the spirit of the board's recommendations. Class 2 operations have been carried out, and the work of the Hannibal and Gannet has partaken to some degree of the nature of class 1 operations, although neither was fitted out exclusively for the purpose. For the present our undertakings must remain oil a modest scale, but we should visualize the possibilities of greater service awaiting more affluent times.
One plan contemplates the installation of the minimum required oceanographic equipment on vessels making regular transoceanic voyages. These vessels could occupy stations during a crossing of an ocean, and such stations could be reoccupied on subsequent voyages. The work might be limited in scope, but it would undoubtedly bring results of very great importance. The cost of this plan would not be great, being governed principally by the delay of the ship for the purpose of making observations. The suggestion has been made that such a vessel should take one sounding a day, which would entail a loss of 3 hours a day during the voyage.
A second plan, and one that can be carried out with the equipment and personnel available, would utilize vessels on special duty to undertake oceanographic work as opportunity offers without too much detriment to the regular duties assigned. This plan has worked out very well for the Navy’s survey vessels, and might well be extended to other vessels when circumstances are favorable or suitable. There would be many occasions when vessels engaged in special work of one kind or another would be able to go out and spend a few hours—perhaps a day or two—in dynamic sounding, or to stop an hour or two while making passage from one locality to another. It would not be difficult to prepare portable equipment for this purpose, but somewhat more difficult to provide trained personnel.
The ideal arrangement would be to equip a vessel exclusively for oceanographic work as described in paragraph 3 of the report of the board on oceanography, with the proper equipment for detailed examination of specific localities for data on currents, temperatures, salinities, and bottom contours, and also for concomitant biological and geological studies. The ship need not be large—consider the successful work of the Coast Guard’s 125-foot General Greene. This vessel’s usefulness would be greater if she were constructed as a nonmagnetic ship. If such a vessel were maintained, it is certain that scientific institutions would be eager to co-operate, to the mutual benefit of all participants.
There are many areas in the oceans concerning which we are in total ignorance. This applies particularly to many areas in the Pacific Ocean where the knowledge of the circulation of the waters and of the contour of the bottom is still very meager. The Navy needs this information and the Navy should be expected to lend a hand in furtherance of more complete knowledge of the oceans.